qid
int64 1
74.7M
| question
stringlengths 0
58.3k
| date
stringlengths 10
10
| metadata
sequence | response_j
stringlengths 2
48.3k
| response_k
stringlengths 2
40.5k
|
|---|---|---|---|---|---|
239,209 | On OS from win 2000 or later (any language) can I assume that this path will always exists?
For example I know that on win xp in some languages the "Program Files" directory have a different name.
So is it true for the System32 folder?
Thanks.
Ohad. | 2008/10/27 | [
"https://Stackoverflow.com/questions/239209",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/17212/"
] | You definitely cannot assume that: Windows could be installed on a different drive letter, or in a different directory. On a previous work PC Windows was installed in D:\WINNT, for example.
The short answer is to use the API call GetSystemDirectory(), which will return the path you are after.
The longer answer is to ask: do you really need to know this? If you're using it to copy files into the Windows directory, I'd suggest you ask if you really want to do this. Copying into the Windows directory is not encouraged, as you can mess up other applications very easily. If you're using the path to find DLLs, why not just rely on the OS to find the appropriate one without giving a path? If you're digging into bits of the OS files, consider: is that going to work in future? In general it's better to not explicitly poke around in the Windows directory if you want your program to work on future Windows versions. | No, you can't assume that.
Windows can be installed to a different path. One solution is to look for it by calling GetSystemDirectory (implemented as part of the Windows API). |
239,209 | On OS from win 2000 or later (any language) can I assume that this path will always exists?
For example I know that on win xp in some languages the "Program Files" directory have a different name.
So is it true for the System32 folder?
Thanks.
Ohad. | 2008/10/27 | [
"https://Stackoverflow.com/questions/239209",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/17212/"
] | Windows can be installed on a different harddrive and or in a different folder. Use the %windir% or %systemroot% environment variables to get you to the windows folder and append system32. Or use the %path% variable, it's usually the first entrance and the preferred method of searching for files such as dlls AFAIK. As per comments: don't rely too much on the system32 dir being the first item. I do think it's safe to assume it's in %path% somewhere though. | It might be safer to use the "windir" environment variable and then append the "System32" to the end of that path. Sometimes windows could be under a different folder or different drive so "windir" will tell you where it is.
As far as i know, the system32 folder should always exist under the windows folder. |
239,209 | On OS from win 2000 or later (any language) can I assume that this path will always exists?
For example I know that on win xp in some languages the "Program Files" directory have a different name.
So is it true for the System32 folder?
Thanks.
Ohad. | 2008/10/27 | [
"https://Stackoverflow.com/questions/239209",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/17212/"
] | You definitely cannot assume that: Windows could be installed on a different drive letter, or in a different directory. On a previous work PC Windows was installed in D:\WINNT, for example.
The short answer is to use the API call GetSystemDirectory(), which will return the path you are after.
The longer answer is to ask: do you really need to know this? If you're using it to copy files into the Windows directory, I'd suggest you ask if you really want to do this. Copying into the Windows directory is not encouraged, as you can mess up other applications very easily. If you're using the path to find DLLs, why not just rely on the OS to find the appropriate one without giving a path? If you're digging into bits of the OS files, consider: is that going to work in future? In general it's better to not explicitly poke around in the Windows directory if you want your program to work on future Windows versions. | I would use the **GetWindowsDirectory** Win32 API to get the current Windows directory, append **System32** to it an then check if it exists. |
239,209 | On OS from win 2000 or later (any language) can I assume that this path will always exists?
For example I know that on win xp in some languages the "Program Files" directory have a different name.
So is it true for the System32 folder?
Thanks.
Ohad. | 2008/10/27 | [
"https://Stackoverflow.com/questions/239209",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/17212/"
] | No, you can't assume that.
Windows can be installed to a different path. One solution is to look for it by calling GetSystemDirectory (implemented as part of the Windows API). | I would use the **GetWindowsDirectory** Win32 API to get the current Windows directory, append **System32** to it an then check if it exists. |
239,209 | On OS from win 2000 or later (any language) can I assume that this path will always exists?
For example I know that on win xp in some languages the "Program Files" directory have a different name.
So is it true for the System32 folder?
Thanks.
Ohad. | 2008/10/27 | [
"https://Stackoverflow.com/questions/239209",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/17212/"
] | You definitely cannot assume that: Windows could be installed on a different drive letter, or in a different directory. On a previous work PC Windows was installed in D:\WINNT, for example.
The short answer is to use the API call GetSystemDirectory(), which will return the path you are after.
The longer answer is to ask: do you really need to know this? If you're using it to copy files into the Windows directory, I'd suggest you ask if you really want to do this. Copying into the Windows directory is not encouraged, as you can mess up other applications very easily. If you're using the path to find DLLs, why not just rely on the OS to find the appropriate one without giving a path? If you're digging into bits of the OS files, consider: is that going to work in future? In general it's better to not explicitly poke around in the Windows directory if you want your program to work on future Windows versions. | Just an FYI, but in a Terminal Server environment (ie, Citrix), GetWindowsDirectory() may return a unique path for a remote user.
[link text](http://msdn.microsoft.com/en-us/library/ms724454(VS.85).aspx)
As more and more companies use virtualized desktops, developers need to keep this in mind. |
239,209 | On OS from win 2000 or later (any language) can I assume that this path will always exists?
For example I know that on win xp in some languages the "Program Files" directory have a different name.
So is it true for the System32 folder?
Thanks.
Ohad. | 2008/10/27 | [
"https://Stackoverflow.com/questions/239209",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/17212/"
] | No, you can't assume that.
Windows can be installed to a different path. One solution is to look for it by calling GetSystemDirectory (implemented as part of the Windows API). | It might be safer to use the "windir" environment variable and then append the "System32" to the end of that path. Sometimes windows could be under a different folder or different drive so "windir" will tell you where it is.
As far as i know, the system32 folder should always exist under the windows folder. |
239,209 | On OS from win 2000 or later (any language) can I assume that this path will always exists?
For example I know that on win xp in some languages the "Program Files" directory have a different name.
So is it true for the System32 folder?
Thanks.
Ohad. | 2008/10/27 | [
"https://Stackoverflow.com/questions/239209",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/17212/"
] | No, you can't assume that.
Windows can be installed to a different path. One solution is to look for it by calling GetSystemDirectory (implemented as part of the Windows API). | Just an FYI, but in a Terminal Server environment (ie, Citrix), GetWindowsDirectory() may return a unique path for a remote user.
[link text](http://msdn.microsoft.com/en-us/library/ms724454(VS.85).aspx)
As more and more companies use virtualized desktops, developers need to keep this in mind. |
44,951,581 | I have a requirement where in the function takes different parameters and returns unique objects. All these functions perform the same operation.
ie.
```
public returnObject1 myfunction( paramObject1 a, int a) {
returnObject1 = new returnObject1();
returnObject1.a = paramObject1.a;
return returnObject1;
}
public returnOject2 myfunction( paramObject2 a, int a){
returnObject2 = new returnObject2();
returnObject2.a = paramObject2.a;
return returnObject2;
}
```
As you can see above, both the function do the same task but they take different parameters as input and return different objects.
I would like to minimize writing different functions that does the same task.
Is it possible to write a generic method for this that can substitute the parameters based on the call to the function?
paramObject and returnObject are basically two classes that have different variables. They are not related to each other.
My objective is that I do not want to do function overloading since the functions do almost the same work. I would like to have a single function that can handle different input and different return output.
my aim is to do something like this (if possible):
```
public static < E > myfunction( T a, int a ) {
// do work
}
```
The return type E and the input T can keep varying. | 2017/07/06 | [
"https://Stackoverflow.com/questions/44951581",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/6512806/"
] | Make `interface Foo` and implement this `interface` in both `paramObject1` and `paramObject2` class. Now your method should be look like:
```
public Foo myFunction(Foo foo, int a){
//Rest of the code.
return foo;
}
``` | you can using the 3rd `apply` method to remove the code duplications, you separate creation & initialization from the `apply` method in this approach. and don't care about which type of `T` is used. for example:
```
returnObject1 myfunction(paramObject1 a, int b) {
return apply(returnObject1::new, b, value -> {
//uses paramObject1
//populates returnObject1
//for example:
value.foo = a.bar;
});
}
returnOject2 myfunction(paramObject2 a, int b) {
return apply(returnOject2::new, b, value -> {
//uses paramObject2
//populates returnObject2
//for example:
value.key = a.value;
});
}
<T> T apply(Supplier<T> factory, int b, Consumer<T> initializer) {
T value = factory.get();
initializer.accept(value);
//does work ...
return value;
}
```
*Note* the 2 `myfunction` is optional, you can remove them from you source code, and call the `apply` method directly, for example:
```
paramObject2 a = ...;
returnObject2 result = apply(returnOject2::new, 2, value -> {
//for example:
value.key = a.value;
});
``` |
37,723,804 | I have to search a contact by name, surname or telephone number.
how can i do that?
I think i can't use java 8 stream in this case...
Another thing... I have to press "2" two times in order to see all the contact list but the if implementation seems right to me.
The code:
```
import java.util.ArrayList;
import java.util.Scanner;
public class Test1 {
public static void main(String args[]) {
Scanner in = new Scanner( System.in );
ArrayList<Contatto> cont = new ArrayList<Contatto>();
int a;
try{
while (true){
System.out.println("Per inserire nuovo contatto premere 1");
System.out.println("Per visionare l'elenco dei contatti premere 2");
System.out.println("Per cercare un contatto premere 3");
a= in.nextInt();
//if you press1 you add new contact
if (a == 1){
cont.add(new Contatto());
}
//if you press2 you'll see all the contact list.
else if (a == 2){
for (Contatto tmp : cont){
String tm = tmp.dammiDettagli(tmp);
System.out.println(tm);
}
}
//if you press 3 you'll be able to search a contact by name or
//surname or telephone number
else if (a == 3){
System.out.println("Cerca contatto:");
}
else {
System.out.println("Inserimento dati errato");
}
}
}finally {
in.close();
}
}
}
```
and this is the public class Contatto:
```
import java.util.Scanner;
public class Contatto {
private String nome;
private String cognome;
private String num_Tel;
Contatto(){
@SuppressWarnings("resource")
Scanner in = new Scanner( System.in );
System.out.println("Creazione nuovo contatto...");
System.out.println("Inserire il nome:");
//set name
setNome(in.next());
System.out.println("Inserire il cognome:");
//set surname
setCognome(in.next());
System.out.println("Inserire il numero di telefono:");
//set telephone number
setNum_Tel(in.next());
}
//method to search contact
public String cercaContatto(String in){
}
public String dammiDettagli(Contatto contatto){
return getNome() +" "+ getCognome() +" "+ getNum_Tel();
}
public String getNome() {
return nome;
}
public void setNome(String nome) {
this.nome = nome;
}
public String getCognome() {
return cognome;
}
public void setCognome(String cognome) {
this.cognome = cognome;
}
public String getNum_Tel() {
return num_Tel;
}
public void setNum_Tel(String num_Tel) {
this.num_Tel = num_Tel;
}
}
``` | 2016/06/09 | [
"https://Stackoverflow.com/questions/37723804",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/6444835/"
] | This could be done in Java 8 as next:
```
Optional<Contatto> result = cont.stream().filter(c ->
(nome == null || nome.equalsIgnoreCase(c.getNome()))
&& (cognome == null || cognome.equalsIgnoreCase(c.getCognome()))
&& (num_Tel == null || num_Tel.equals(c.getNum_Tel()))
).findFirst();
```
Assuming that `nome`, `cognome` and `num_Tel` are `String` representing your query's criteria.
If `nome`, `cognome` and `num_Tel` are `Optional<String>` representing your query's criteria, it will then be:
```
Optional<Contatto> result = cont.stream().filter(c ->
nome.map(s -> s.equalsIgnoreCase(c.getNome())).orElse(true)
&& cognome.map(s -> s.equalsIgnoreCase(c.getCognome())).orElse(true)
&& num_Tel.map(s -> s.equals(c.getNum_Tel())).orElse(true)
).findFirst();
``` | You can Add a method for each type of search that you are performing and call that method in choice "3". The method is simple and pretty straightforward, for example, for searching by phone number
```
private static Contatto SearchContattoNumber( ArrayList<Contatto> cont, int number ) {
for (Contatto tmp : cont){
if (tmp.getNum_Tel() == number) return tmp;
}
return null;
}
```
And you would create such a method for each Search option, and then decide which search you're gonna use by asking the user just like you did ask for what operation you will perform |
11,276,112 | Does anyone know if its possible to add specific files uncompressed to a Android APK file during the ANT build process using build.xml? All my files live in the *assets* folder and use the same extension. I do realise that i could use a different extension for the files that i don't want to be added compressed and specify, for example:
```
<nocompress extension="NoCompress" />
```
but this currently isn't an option for me.
I tried adding my own *aapt add* step after the *appt package* step in the *package-resource* section in *build.xml*:
```
<exec executable="${aapt}" taskName="add">
<arg value="add" />
<arg value="-v" />
<arg value="${out.absolute.dir}/TestAndroid.ap_" />
<arg value="${asset.absolute.dir}/notcompressed.and" />
</exec>
```
Which did add the file to the APK but it was compressed. :)
Is this possible or is a different extension the only way?
Thanks! | 2012/06/30 | [
"https://Stackoverflow.com/questions/11276112",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/1184595/"
] | Have a look [here](http://ponystyle.com/blog/2010/03/26/dealing-with-asset-compression-in-android-apps/)
>
> The only way (that I’ve discovered, as of this writing) to control
> this behavior is by using the -0 (zero) flag to aapt on the command
> line. This flag, passed without any accompanying argument, will tell
> aapt to disable compression for all types of assets. Typically you
> will not want to use this exact option, because for most assets,
> compression is a desirable thing. Sometimes, however, you will have a
> specific type of asset (say, a database), that you do not want to
> apply compression to. In this case, you have two options.
>
>
> First, you can give your asset file an extension in the list above.
> While this does not necessarily make sense, it can be an easy
> workaround if you don’t want to deal with aapt on the command line.
> The other option is to pass a specific extension to the -0 flag, such
> as -0 db, to disable compression for assets with that extension. You
> can pass the -0 flag multiple times, and each time with a separate
> extension, if you need more than one type to be uncompressed.
>
>
> Currently, there is no way to pass these extra flags to aapt when
> using the ADT within Eclipse, so if you don’t want to sacrifice the
> ease of use of the GUI tools, you will have to go with the first
> option, and rename your file’s extension.
>
>
> | Just to provide closure for this one.
I don't think it is possible to mark individual files to be added uncompressed to the APK.
Being able to mark individual files as uncompressed to *aapt* could be useful. As would the addition of a *nocompress file* tag, eg:
```
<nocompress file="FileNoCompress.abc" />
```
:) |
11,276,112 | Does anyone know if its possible to add specific files uncompressed to a Android APK file during the ANT build process using build.xml? All my files live in the *assets* folder and use the same extension. I do realise that i could use a different extension for the files that i don't want to be added compressed and specify, for example:
```
<nocompress extension="NoCompress" />
```
but this currently isn't an option for me.
I tried adding my own *aapt add* step after the *appt package* step in the *package-resource* section in *build.xml*:
```
<exec executable="${aapt}" taskName="add">
<arg value="add" />
<arg value="-v" />
<arg value="${out.absolute.dir}/TestAndroid.ap_" />
<arg value="${asset.absolute.dir}/notcompressed.and" />
</exec>
```
Which did add the file to the APK but it was compressed. :)
Is this possible or is a different extension the only way?
Thanks! | 2012/06/30 | [
"https://Stackoverflow.com/questions/11276112",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/1184595/"
] | If building using gradle, then it seems you can provide the aapt flags like this:
```
android {
aaptOptions {
noCompress 'foo', 'bar'
ignoreAssetsPattern "!.svn:!.git:!.ds_store:!*.scc:.*:<dir>_*:!CVS:!thumbs.db:!picasa.ini:!*~"
}
}
```
<http://tools.android.com/tech-docs/new-build-system/user-guide#TOC-aapt-options> | Just to provide closure for this one.
I don't think it is possible to mark individual files to be added uncompressed to the APK.
Being able to mark individual files as uncompressed to *aapt* could be useful. As would the addition of a *nocompress file* tag, eg:
```
<nocompress file="FileNoCompress.abc" />
```
:) |
62,043,889 | When I tried to use keras to build a simple autoencoder, I found something strange between keras and tf.keras.
```
tf.__version__
```
2.2.0
```
(x_train,_), (x_test,_) = tf.keras.datasets.mnist.load_data()
x_train = x_train.astype('float32') / 255.
x_test = x_test.astype('float32') / 255.
x_train = x_train.reshape((len(x_train), 784))
x_test = x_test.reshape((len(x_test), 784)) # None, 784
```
The original picture
```
plt.imshow(x_train[0].reshape(28, 28), cmap='gray')
```
[enter image description here](https://i.stack.imgur.com/J8xc0.png)
```
import keras
# import tensorflow.keras as keras
my_autoencoder = keras.models.Sequential([
keras.layers.Dense(64, input_shape=(784, ), activation='relu'),
keras.layers.Dense(784, activation='sigmoid')
])
my_autoencoder.compile(optimizer='adadelta', loss='binary_crossentropy')
my_autoencoder.fit(x_train, x_train, epochs=10, shuffle=True, validation_data=(x_test, x_test))
```
training
```
Train on 60000 samples, validate on 10000 samples
Epoch 1/10
60000/60000 [==============================] - 7s 112us/step - loss: 0.2233 - val_loss: 0.1670
Epoch 2/10
60000/60000 [==============================] - 7s 111us/step - loss: 0.1498 - val_loss: 0.1337
Epoch 3/10
60000/60000 [==============================] - 7s 110us/step - loss: 0.1254 - val_loss: 0.1152
Epoch 4/10
60000/60000 [==============================] - 7s 110us/step - loss: 0.1103 - val_loss: 0.1032
Epoch 5/10
60000/60000 [==============================] - 7s 110us/step - loss: 0.1010 - val_loss: 0.0963
Epoch 6/10
60000/60000 [==============================] - 7s 109us/step - loss: 0.0954 - val_loss: 0.0919
Epoch 7/10
60000/60000 [==============================] - 7s 109us/step - loss: 0.0917 - val_loss: 0.0889
Epoch 8/10
60000/60000 [==============================] - 7s 110us/step - loss: 0.0890 - val_loss: 0.0866
Epoch 9/10
60000/60000 [==============================] - 7s 110us/step - loss: 0.0870 - val_loss: 0.0850
Epoch 10/10
60000/60000 [==============================] - 7s 109us/step - loss: 0.0853 - val_loss: 0.0835
```
the decoded image with keras
```
temp = my_autoencoder.predict(x_train)
plt.imshow(temp[0].reshape(28, 28), cmap='gray')
```
[enter image description here](https://i.stack.imgur.com/BUR8Q.png)
So far, everything is as normal as expected, but something is weird when I replaced keras with tf.keras
```
# import keras
import tensorflow.keras as keras
my_autoencoder = keras.models.Sequential([
keras.layers.Dense(64, input_shape=(784, ), activation='relu'),
keras.layers.Dense(784, activation='sigmoid')
])
my_autoencoder.compile(optimizer='adadelta', loss='binary_crossentropy')
my_autoencoder.fit(x_train, x_train, epochs=10, shuffle=True, validation_data=(x_test, x_test))
```
training
```
Epoch 1/10
1875/1875 [==============================] - 5s 3ms/step - loss: 0.6952 - val_loss: 0.6940
Epoch 2/10
1875/1875 [==============================] - 5s 3ms/step - loss: 0.6929 - val_loss: 0.6918
Epoch 3/10
1875/1875 [==============================] - 5s 3ms/step - loss: 0.6907 - val_loss: 0.6896
Epoch 4/10
1875/1875 [==============================] - 5s 3ms/step - loss: 0.6885 - val_loss: 0.6873
Epoch 5/10
1875/1875 [==============================] - 5s 3ms/step - loss: 0.6862 - val_loss: 0.6848
Epoch 6/10
1875/1875 [==============================] - 5s 3ms/step - loss: 0.6835 - val_loss: 0.6818
Epoch 7/10
1875/1875 [==============================] - 5s 3ms/step - loss: 0.6802 - val_loss: 0.6782
Epoch 8/10
1875/1875 [==============================] - 5s 3ms/step - loss: 0.6763 - val_loss: 0.6737
Epoch 9/10
1875/1875 [==============================] - 5s 3ms/step - loss: 0.6714 - val_loss: 0.6682
Epoch 10/10
1875/1875 [==============================] - 5s 3ms/step - loss: 0.6652 - val_loss: 0.6612
```
the decoded image with tf.keras
```
temp = my_autoencoder.predict(x_train)
plt.imshow(temp[0].reshape(28, 28), cmap='gray')
```
[enter image description here](https://i.stack.imgur.com/wNey4.png)
I can't find anything wrong, does anyone know why? | 2020/05/27 | [
"https://Stackoverflow.com/questions/62043889",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/9909121/"
] | The true culprit is the default learning rate used by [`keras.Adadelta`](https://github.com/keras-team/keras/blob/master/keras/optimizers.py#L401) vs [`tf.keras.Adadelta`](https://github.com/tensorflow/tensorflow/blob/r2.2/tensorflow/python/keras/optimizer_v2/adadelta.py#L63): `1` vs `1e-4` - see below. It's true that `keras` and `tf.keras` implementations differ a bit, but difference in results can't be as dramatic as you observed (only in a different configuration, e.g. learning rate).
You can confirm this in your original code by running `print(model.optimizer.get_config())`.
```py
import matplotlib.pyplot as plt
import tensorflow as tf
import tensorflow.keras as keras
(x_train, _), (x_test, _) = tf.keras.datasets.mnist.load_data()
x_train = x_train.astype('float32') / 255.
x_test = x_test.astype('float32') / 255.
x_train = x_train.reshape((len(x_train), 784))
x_test = x_test.reshape((len(x_test), 784)) # None, 784
###############################################################################
model = keras.models.Sequential([
keras.layers.Dense(64, input_shape=(784, ), activation='relu'),
keras.layers.Dense(784, activation='sigmoid')
])
model.compile(optimizer=keras.optimizers.Adadelta(learning_rate=1),
loss='binary_crossentropy')
model.fit(x_train, x_train, epochs=10, shuffle=True,
validation_data=(x_test, x_test))
###############################################################################
temp = model.predict(x_train)
plt.imshow(temp[0].reshape(28, 28), cmap='gray')
```
```py
Epoch 1/10
1875/1875 [==============================] - 4s 2ms/step - loss: 0.2229 - val_loss: 0.1668
Epoch 2/10
1875/1875 [==============================] - 3s 2ms/step - loss: 0.1497 - val_loss: 0.1337
Epoch 3/10
1875/1875 [==============================] - 3s 2ms/step - loss: 0.1253 - val_loss: 0.1152
Epoch 4/10
1875/1875 [==============================] - 3s 2ms/step - loss: 0.1103 - val_loss: 0.1033
Epoch 5/10
1875/1875 [==============================] - 3s 2ms/step - loss: 0.1009 - val_loss: 0.0962
Epoch 6/10
1875/1875 [==============================] - 3s 2ms/step - loss: 0.0952 - val_loss: 0.0916
Epoch 7/10
1875/1875 [==============================] - 3s 2ms/step - loss: 0.0914 - val_loss: 0.0885
Epoch 8/10
1875/1875 [==============================] - 3s 2ms/step - loss: 0.0886 - val_loss: 0.0862
Epoch 9/10
1875/1875 [==============================] - 3s 2ms/step - loss: 0.0865 - val_loss: 0.0844
Epoch 10/10
1875/1875 [==============================] - 3s 2ms/step - loss: 0.0849 - val_loss: 0.0830
```
 | If you use `adam`, the `tf.keras` model performs better. (`keras` and `tf.keras` uses two different version of the optimizers)
Most probably, it has to do with `momentum` for convergence for this data. It is very slow, maybe you'll need to train for more epochs with higher learning rate.
Here's an answer why adadelta should be avoided : [How to set parameters of the Adadelta Algorithm in Tensorflow correctly?](https://stackoverflow.com/questions/38632536/how-to-set-parameters-of-the-adadelta-algorithm-in-tensorflow-correctly)
```
import tensorflow as tf
(x_train,_), (x_test,_) = tf.keras.datasets.mnist.load_data()
x_train = x_train.astype('float32') / 255.
x_test = x_test.astype('float32') / 255.
x_train = x_train.reshape((len(x_train), 784))
x_test = x_test.reshape((len(x_test), 784)) # None, 784
# import keras
import tensorflow.keras as keras
my_autoencoder = keras.models.Sequential([
keras.layers.Dense(64, input_shape=(784, ), activation='relu'),
keras.layers.Dense(784, activation='sigmoid')
])
my_autoencoder.compile(optimizer='adam', loss='binary_crossentropy')
my_autoencoder.fit(x_train, x_train, epochs=10, shuffle=True, validation_data=(x_test, x_test))
```
```
Epoch 1/10
1875/1875 [==============================] - 5s 3ms/step - loss: 0.1372 - val_loss: 0.0909
Epoch 2/10
1875/1875 [==============================] - 5s 3ms/step - loss: 0.0840 - val_loss: 0.0782
Epoch 3/10
1875/1875 [==============================] - 5s 3ms/step - loss: 0.0773 - val_loss: 0.0753
Epoch 4/10
1875/1875 [==============================] - 5s 3ms/step - loss: 0.0754 - val_loss: 0.0742
Epoch 5/10
1875/1875 [==============================] - 5s 3ms/step - loss: 0.0747 - val_loss: 0.0738
Epoch 6/10
1875/1875 [==============================] - 5s 3ms/step - loss: 0.0744 - val_loss: 0.0735
Epoch 7/10
1875/1875 [==============================] - 5s 3ms/step - loss: 0.0741 - val_loss: 0.0734
Epoch 8/10
1875/1875 [==============================] - 5s 3ms/step - loss: 0.0740 - val_loss: 0.0733
Epoch 9/10
1875/1875 [==============================] - 5s 3ms/step - loss: 0.0738 - val_loss: 0.0731
Epoch 10/10
1875/1875 [==============================] - 5s 3ms/step - loss: 0.0737 - val_loss: 0.0734
<tensorflow.python.keras.callbacks.History at 0x7f8c83d907b8>
```
N.B: `keras` and `tf.keras` have slightly different implementations for `Model`, so internally they call different functions, the performance can vary, it's no surprise.
In fact, the problem is with the optimizer, not the model, to validate that, you can try training a `keras` model with `tf` AdaDelta, it will also show poor results.
```
import keras
# import tensorflow.keras as keras
my_autoencoder = keras.models.Sequential([
keras.layers.Dense(64, input_shape=(784, ), activation='relu'),
keras.layers.Dense(784, activation='sigmoid')
])
my_autoencoder.compile(tf.keras.optimizers.Adadelta(), loss='binary_crossentropy')
my_autoencoder.fit(x_train, x_train, epochs=10, shuffle=True, validation_data=(x_test, x_test))
```
```
Train on 60000 samples, validate on 10000 samples
Epoch 1/10
60000/60000 [==============================] - 6s 101us/step - loss: 0.6955 - val_loss: 0.6946
Epoch 2/10
60000/60000 [==============================] - 6s 99us/step - loss: 0.6936 - val_loss: 0.6927
Epoch 3/10
60000/60000 [==============================] - 6s 100us/step - loss: 0.6919 - val_loss: 0.6910
Epoch 4/10
60000/60000 [==============================] - 6s 96us/step - loss: 0.6901 - val_loss: 0.6892
Epoch 5/10
60000/60000 [==============================] - 6s 94us/step - loss: 0.6883 - val_loss: 0.6873
Epoch 6/10
60000/60000 [==============================] - 6s 95us/step - loss: 0.6863 - val_loss: 0.6851
Epoch 7/10
60000/60000 [==============================] - 6s 101us/step - loss: 0.6839 - val_loss: 0.6825
Epoch 8/10
60000/60000 [==============================] - 6s 101us/step - loss: 0.6812 - val_loss: 0.6794
Epoch 9/10
60000/60000 [==============================] - 6s 99us/step - loss: 0.6778 - val_loss: 0.6756
Epoch 10/10
60000/60000 [==============================] - 6s 101us/step - loss: 0.6736 - val_loss: 0.6710
<keras.callbacks.callbacks.History at 0x7f8c805bbe10>
```
`keras` and `tf.keras` calls two different optimizers when the optimizer parameter is passed as a string.
```
import tensorflow as tf
# import tensorflow.keras as keras
my_autoencoder = tf.keras.models.Sequential([
tf.keras.layers.Dense(64, input_shape=(784, ), activation='relu'),
tf.keras.layers.Dense(784, activation='sigmoid')
])
my_autoencoder.compile('adadelta', loss='binary_crossentropy')
my_autoencoder.fit(x_train, x_train, epochs=1, shuffle=True, validation_data=(x_test, x_test))
my_autoencoder.optimizer
```
`<tensorflow.python.keras.optimizer_v2.adadelta.Adadelta at 0x7f8c7fc3ce80>`
```
import keras
# import tensorflow.keras as keras
my_autoencoder = keras.models.Sequential([
keras.layers.Dense(64, input_shape=(784, ), activation='relu'),
keras.layers.Dense(784, activation='sigmoid')
])
my_autoencoder.compile('adadelta', loss='binary_crossentropy')
my_autoencoder.fit(x_train, x_train, epochs=1, shuffle=True, validation_data=(x_test, x_test))
my_autoencoder.optimizer
```
`<keras.optimizers.Adadelta at 0x7f8c7fc3c908>`
So, the confusion can be avoided by importing the optimizer separately. |
17,357,665 | I have **two tables** for one is `category` and another one is `sub-category`. that two table is assigned to `FK` for many table. In some situation we will move one record of **sub-category** to **main category**. so this time occur constraints error because that **key** associated with other table. so i would not create this **schema**.
so now i plan to **create category** and **sub-category** in same table and **create relationship table** to make relationship between them.
`category table:`
```
id(PK,AUTO Increment),
item===>((1,phone),(2.computer),(3,ios),(4,android),(5,software),(6,hardware)).
```
`relationship table:`
```
id,cate_id(FK),
parentid(refer from category table)===>((1,1,0),(2,2,0),(3,3,1),
(4,4,1),(5,5,2),(5,5,3)).
```
in my side wouldnot go hierarchy level more than three.
if we easily move to subcategory to main category `ex:(4,4,1) to (4,4,0)` without affect any other table. is this good procedure?
if we will maintain millions record, will we face any other problem in future?
have any another idea means let me know? | 2013/06/28 | [
"https://Stackoverflow.com/questions/17357665",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/1089410/"
] | There might be a problem if you have multiple levels in the tree, and want to find all the subcategories of any category. This would require either multiple queries, or a recursive one.
You could instead look into the ["Nested Sets"](http://www.codeproject.com/Articles/4155/Improve-hierarchy-performance-using-nested-sets) data-structure. It supports effective querying of any sub-tree. It does have a costly update, but updates probably won't happen very often. If need be, you could batch the updates and run them over night.
```
create table Category (
Id int not null primary key auto_increment,
LeftExtent int not null,
RightExtent int not null,
Name varchar(100) not null
);
create table PendingCategoryUpdate (
Id int not null primary key auto_increment,
ParentCategoryId int null references Category ( Id ),
ParentPendingId int null references PendingCategoryUpdate ( Id ),
Name varchar(100) not null
);
```
---
If you have a small number of categories, a normal parent reference should be enough. You could even read the categories into memory for processing.
```
create table Category (
Id int not null primary key auto_increment,
ParentId int null references Category ( Id ),
Name varchar(100) not null
);
-- Just an example
create table Record (
Id int not null primary key auto_increment,
CategoryId int not null references Category ( Id )
);
select *
from Record
where CategoryId in (1, 2, 3); -- All the categories in the chosen sub-tree
``` | How about creating one table as following:
```
categories(
id int not null auto_increment primary key,
name char(10),
parent_id int not null default 0)
```
Where parent\_id is a FK to the id, which is the PK of the table.
When parent\_id is 0, then this category is a main one. When it is > 0, this is a sub category of this parent.
To find the parent of a category, you will do self-join. |
35,317,633 | I'm trying to write what must be the simplest angular directive which displays a Yes/No select list and is bound to a model containing a boolean value. Unfortunately the existing value is never preselected. My directive reads
```
return {
restrict: 'E',
replace: true,
template: '<select class="form-control"><option value="true">Yes</option><option value="false">No</option></select>',
scope: {
ngModel: '='
}
}
```
and I am calling the directive as
```
<yesno ng-model="brand.is_anchor"></yesno>
```
The select options display and the generated HTML reads as
```
<select class="form-control ng-isolate-scope ng-valid" ng-model="brand.is_anchor">
<option value="? boolean:false ?"></option>
<option value="true">Yes</option>
<option value="false">No</option>
</select>
```
The initial value of the bound model is "false" but it always displays an empty option and per the first option listed in the generated HTML.
Can anybody please advise? | 2016/02/10 | [
"https://Stackoverflow.com/questions/35317633",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/1298045/"
] | There is no need for a custom sentinel image, or messing with the network. See my [redis-ha-learning](https://github.com/asarkar/spring/tree/master/redis-ha-learning) project using [Spring Data Redis](https://docs.spring.io/spring-data/data-redis/docs/current/reference/html/#reference), [bitnami/redis](https://hub.docker.com/r/bitnami/redis) and [bitnami/redis-sentinel](https://hub.docker.com/r/bitnami/redis-sentinel) images. The Docker Compose file is [here](https://github.com/asarkar/spring/blob/master/redis-ha-learning/redis-sentinel.yaml).
My code auto detects the sentinels based on the Docker Compose container names. | So, the solution that worked for me is simply reading the /etc/hosts file on the source container. I busy wait till the link is established and then use that network interface IP to start the sentinel process. This is just a stop gap solution and it is not scalable. Redis-sentinel is still not production ready in dockerizable format as confirmed in this [post](https://stackoverflow.com/questions/25914814/redis-sentinel-docker-image-dockerfile%20post). So I decided to install Redis/sentinel on the physical hosts. |
35,317,633 | I'm trying to write what must be the simplest angular directive which displays a Yes/No select list and is bound to a model containing a boolean value. Unfortunately the existing value is never preselected. My directive reads
```
return {
restrict: 'E',
replace: true,
template: '<select class="form-control"><option value="true">Yes</option><option value="false">No</option></select>',
scope: {
ngModel: '='
}
}
```
and I am calling the directive as
```
<yesno ng-model="brand.is_anchor"></yesno>
```
The select options display and the generated HTML reads as
```
<select class="form-control ng-isolate-scope ng-valid" ng-model="brand.is_anchor">
<option value="? boolean:false ?"></option>
<option value="true">Yes</option>
<option value="false">No</option>
</select>
```
The initial value of the bound model is "false" but it always displays an empty option and per the first option listed in the generated HTML.
Can anybody please advise? | 2016/02/10 | [
"https://Stackoverflow.com/questions/35317633",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/1298045/"
] | I have this configuration example here using docker compose that can be of help.
<https://github.com/oneyottabyte/redis_sentinel> | So, the solution that worked for me is simply reading the /etc/hosts file on the source container. I busy wait till the link is established and then use that network interface IP to start the sentinel process. This is just a stop gap solution and it is not scalable. Redis-sentinel is still not production ready in dockerizable format as confirmed in this [post](https://stackoverflow.com/questions/25914814/redis-sentinel-docker-image-dockerfile%20post). So I decided to install Redis/sentinel on the physical hosts. |
319,327 | 
This problem has bothered me for quite some time and I can't solve it. I have even tried to make a construction, but it sometimes tips to the left and sometimes tips to the right :).
When we submerge the body in the water the water pushes it up. That is an action. At the same time the body pushes water down. That is a reaction. So the balance should be maintained.
But, since the water level rises the hydrostatic pressure on the bottom is greater so the right side should go down.
There is another similar problem but it's not the same.
Please help. | 2017/03/16 | [
"https://physics.stackexchange.com/questions/319327",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/145936/"
] | Let $V$ be the volume of the hanging block, $A$ the area of the water surface, $\rho$ the density of water, and $g$ the acceleration due to gravity.
The extra hydrostatic force felt by the bottom of the container after lowering the block is
$$\Delta F = \rho gA\Delta h,$$
where $\Delta h$ is the change in water height ($\rho g \Delta h$ would be the change in hydrostatic pressure). Because water is not compressible, $A\Delta h$ must be the volume of the submerged block.
$$\Delta F = \rho g V.$$
Notice that this is exactly equal to the buoyant force on the block, so the two new forces created after the block is submerged negate each other. | EDIT:
-----
Since this answer is not being very well received I will just say that *if* we neglect gravitational forces due to the height difference between the mass in the upper and lower pictures; then yes, the scales *will* be balanced as there is simply no net torque.
---
However, since the question did **not** stipulate these assumptions then the answer below is the correct one:
Look at the RHS of the scale and consider Newton's Law of Gravitation $$F=-\frac{G \cdot m\cdot m\_E}{d^2}$$ On the RHS consider $m$ to be the mass of block suspended by the string and $m\_E$ is the mass of the Earth $\approx 6\times 10^{24}$kg. $G$ is the gravitational constant and $d$ is the distance of the string between the block in the top picture and the one in the bottom *plus* the distance to the centre of the earth.
Now let $m\_{s}$ be the mass of the submerged block in the container of the lower RHS and $d\_E$ is the distance to the centre of the earth.
$$F=-\frac{G \cdot m\_{s}\cdot m\_E}{d\_E^2}$$
The gravitational force acting on the RHS of lower system is therefore greater by Newton's inverse square law.
Can you now understand why once the block is dropped into the fluid the RHS of the lower image will weigh more and hence tilt clockwise? |
319,327 | 
This problem has bothered me for quite some time and I can't solve it. I have even tried to make a construction, but it sometimes tips to the left and sometimes tips to the right :).
When we submerge the body in the water the water pushes it up. That is an action. At the same time the body pushes water down. That is a reaction. So the balance should be maintained.
But, since the water level rises the hydrostatic pressure on the bottom is greater so the right side should go down.
There is another similar problem but it's not the same.
Please help. | 2017/03/16 | [
"https://physics.stackexchange.com/questions/319327",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/145936/"
] | **The scale will not move.**
You don't need to think about buoyancy at all to answer this question. In the first picture, the scale is balanced, because the net force on each side (the weight) is equal. No mass is added to or removed from either side, so the net forces remain the same. | So various forces neglected (including gravity, air resistance, thermal forces, air pressure) - but your question suggest this is an inquiry about the effect of bouyancy.
That being the case, lowering the mass into the water brings into effect its bouyancy. This is a force lifting the mass and acting down on the water.
However, as the mass is tethered to the scale the force acting down the string is reduced by the same amount as the bouyancy, and the net effect on the scale is zero.
(Also neglecting rotating frames of reference, light pressure, stress and young's modulus, magnetically induce currents etc) |
319,327 | 
This problem has bothered me for quite some time and I can't solve it. I have even tried to make a construction, but it sometimes tips to the left and sometimes tips to the right :).
When we submerge the body in the water the water pushes it up. That is an action. At the same time the body pushes water down. That is a reaction. So the balance should be maintained.
But, since the water level rises the hydrostatic pressure on the bottom is greater so the right side should go down.
There is another similar problem but it's not the same.
Please help. | 2017/03/16 | [
"https://physics.stackexchange.com/questions/319327",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/145936/"
] | So various forces neglected (including gravity, air resistance, thermal forces, air pressure) - but your question suggest this is an inquiry about the effect of bouyancy.
That being the case, lowering the mass into the water brings into effect its bouyancy. This is a force lifting the mass and acting down on the water.
However, as the mass is tethered to the scale the force acting down the string is reduced by the same amount as the bouyancy, and the net effect on the scale is zero.
(Also neglecting rotating frames of reference, light pressure, stress and young's modulus, magnetically induce currents etc) | Let $V$ be the volume of the hanging block, $A$ the area of the water surface, $\rho$ the density of water, and $g$ the acceleration due to gravity.
The extra hydrostatic force felt by the bottom of the container after lowering the block is
$$\Delta F = \rho gA\Delta h,$$
where $\Delta h$ is the change in water height ($\rho g \Delta h$ would be the change in hydrostatic pressure). Because water is not compressible, $A\Delta h$ must be the volume of the submerged block.
$$\Delta F = \rho g V.$$
Notice that this is exactly equal to the buoyant force on the block, so the two new forces created after the block is submerged negate each other. |
319,327 | 
This problem has bothered me for quite some time and I can't solve it. I have even tried to make a construction, but it sometimes tips to the left and sometimes tips to the right :).
When we submerge the body in the water the water pushes it up. That is an action. At the same time the body pushes water down. That is a reaction. So the balance should be maintained.
But, since the water level rises the hydrostatic pressure on the bottom is greater so the right side should go down.
There is another similar problem but it's not the same.
Please help. | 2017/03/16 | [
"https://physics.stackexchange.com/questions/319327",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/145936/"
] | So various forces neglected (including gravity, air resistance, thermal forces, air pressure) - but your question suggest this is an inquiry about the effect of bouyancy.
That being the case, lowering the mass into the water brings into effect its bouyancy. This is a force lifting the mass and acting down on the water.
However, as the mass is tethered to the scale the force acting down the string is reduced by the same amount as the bouyancy, and the net effect on the scale is zero.
(Also neglecting rotating frames of reference, light pressure, stress and young's modulus, magnetically induce currents etc) | EDIT:
-----
Since this answer is not being very well received I will just say that *if* we neglect gravitational forces due to the height difference between the mass in the upper and lower pictures; then yes, the scales *will* be balanced as there is simply no net torque.
---
However, since the question did **not** stipulate these assumptions then the answer below is the correct one:
Look at the RHS of the scale and consider Newton's Law of Gravitation $$F=-\frac{G \cdot m\cdot m\_E}{d^2}$$ On the RHS consider $m$ to be the mass of block suspended by the string and $m\_E$ is the mass of the Earth $\approx 6\times 10^{24}$kg. $G$ is the gravitational constant and $d$ is the distance of the string between the block in the top picture and the one in the bottom *plus* the distance to the centre of the earth.
Now let $m\_{s}$ be the mass of the submerged block in the container of the lower RHS and $d\_E$ is the distance to the centre of the earth.
$$F=-\frac{G \cdot m\_{s}\cdot m\_E}{d\_E^2}$$
The gravitational force acting on the RHS of lower system is therefore greater by Newton's inverse square law.
Can you now understand why once the block is dropped into the fluid the RHS of the lower image will weigh more and hence tilt clockwise? |
319,327 | 
This problem has bothered me for quite some time and I can't solve it. I have even tried to make a construction, but it sometimes tips to the left and sometimes tips to the right :).
When we submerge the body in the water the water pushes it up. That is an action. At the same time the body pushes water down. That is a reaction. So the balance should be maintained.
But, since the water level rises the hydrostatic pressure on the bottom is greater so the right side should go down.
There is another similar problem but it's not the same.
Please help. | 2017/03/16 | [
"https://physics.stackexchange.com/questions/319327",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/145936/"
] | **The scale will not move.**
You don't need to think about buoyancy at all to answer this question. In the first picture, the scale is balanced, because the net force on each side (the weight) is equal. No mass is added to or removed from either side, so the net forces remain the same. | EDIT:
-----
Since this answer is not being very well received I will just say that *if* we neglect gravitational forces due to the height difference between the mass in the upper and lower pictures; then yes, the scales *will* be balanced as there is simply no net torque.
---
However, since the question did **not** stipulate these assumptions then the answer below is the correct one:
Look at the RHS of the scale and consider Newton's Law of Gravitation $$F=-\frac{G \cdot m\cdot m\_E}{d^2}$$ On the RHS consider $m$ to be the mass of block suspended by the string and $m\_E$ is the mass of the Earth $\approx 6\times 10^{24}$kg. $G$ is the gravitational constant and $d$ is the distance of the string between the block in the top picture and the one in the bottom *plus* the distance to the centre of the earth.
Now let $m\_{s}$ be the mass of the submerged block in the container of the lower RHS and $d\_E$ is the distance to the centre of the earth.
$$F=-\frac{G \cdot m\_{s}\cdot m\_E}{d\_E^2}$$
The gravitational force acting on the RHS of lower system is therefore greater by Newton's inverse square law.
Can you now understand why once the block is dropped into the fluid the RHS of the lower image will weigh more and hence tilt clockwise? |
319,327 | 
This problem has bothered me for quite some time and I can't solve it. I have even tried to make a construction, but it sometimes tips to the left and sometimes tips to the right :).
When we submerge the body in the water the water pushes it up. That is an action. At the same time the body pushes water down. That is a reaction. So the balance should be maintained.
But, since the water level rises the hydrostatic pressure on the bottom is greater so the right side should go down.
There is another similar problem but it's not the same.
Please help. | 2017/03/16 | [
"https://physics.stackexchange.com/questions/319327",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/145936/"
] | If you consider everything put in the right side of balance scale as one system, only the internal forces are changed which will not affect the balance.
No external force is applied and hence the balance will be maintained. | Let $V$ be the volume of the hanging block, $A$ the area of the water surface, $\rho$ the density of water, and $g$ the acceleration due to gravity.
The extra hydrostatic force felt by the bottom of the container after lowering the block is
$$\Delta F = \rho gA\Delta h,$$
where $\Delta h$ is the change in water height ($\rho g \Delta h$ would be the change in hydrostatic pressure). Because water is not compressible, $A\Delta h$ must be the volume of the submerged block.
$$\Delta F = \rho g V.$$
Notice that this is exactly equal to the buoyant force on the block, so the two new forces created after the block is submerged negate each other. |
319,327 | 
This problem has bothered me for quite some time and I can't solve it. I have even tried to make a construction, but it sometimes tips to the left and sometimes tips to the right :).
When we submerge the body in the water the water pushes it up. That is an action. At the same time the body pushes water down. That is a reaction. So the balance should be maintained.
But, since the water level rises the hydrostatic pressure on the bottom is greater so the right side should go down.
There is another similar problem but it's not the same.
Please help. | 2017/03/16 | [
"https://physics.stackexchange.com/questions/319327",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/145936/"
] | The balance will be maintained because there is no EXTERNAL force applied on left or right side. This is because of the same reason you can't push a car while sitting in it! | So various forces neglected (including gravity, air resistance, thermal forces, air pressure) - but your question suggest this is an inquiry about the effect of bouyancy.
That being the case, lowering the mass into the water brings into effect its bouyancy. This is a force lifting the mass and acting down on the water.
However, as the mass is tethered to the scale the force acting down the string is reduced by the same amount as the bouyancy, and the net effect on the scale is zero.
(Also neglecting rotating frames of reference, light pressure, stress and young's modulus, magnetically induce currents etc) |
319,327 | 
This problem has bothered me for quite some time and I can't solve it. I have even tried to make a construction, but it sometimes tips to the left and sometimes tips to the right :).
When we submerge the body in the water the water pushes it up. That is an action. At the same time the body pushes water down. That is a reaction. So the balance should be maintained.
But, since the water level rises the hydrostatic pressure on the bottom is greater so the right side should go down.
There is another similar problem but it's not the same.
Please help. | 2017/03/16 | [
"https://physics.stackexchange.com/questions/319327",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/145936/"
] | The balance will be maintained because there is no EXTERNAL force applied on left or right side. This is because of the same reason you can't push a car while sitting in it! | EDIT:
-----
Since this answer is not being very well received I will just say that *if* we neglect gravitational forces due to the height difference between the mass in the upper and lower pictures; then yes, the scales *will* be balanced as there is simply no net torque.
---
However, since the question did **not** stipulate these assumptions then the answer below is the correct one:
Look at the RHS of the scale and consider Newton's Law of Gravitation $$F=-\frac{G \cdot m\cdot m\_E}{d^2}$$ On the RHS consider $m$ to be the mass of block suspended by the string and $m\_E$ is the mass of the Earth $\approx 6\times 10^{24}$kg. $G$ is the gravitational constant and $d$ is the distance of the string between the block in the top picture and the one in the bottom *plus* the distance to the centre of the earth.
Now let $m\_{s}$ be the mass of the submerged block in the container of the lower RHS and $d\_E$ is the distance to the centre of the earth.
$$F=-\frac{G \cdot m\_{s}\cdot m\_E}{d\_E^2}$$
The gravitational force acting on the RHS of lower system is therefore greater by Newton's inverse square law.
Can you now understand why once the block is dropped into the fluid the RHS of the lower image will weigh more and hence tilt clockwise? |
319,327 | 
This problem has bothered me for quite some time and I can't solve it. I have even tried to make a construction, but it sometimes tips to the left and sometimes tips to the right :).
When we submerge the body in the water the water pushes it up. That is an action. At the same time the body pushes water down. That is a reaction. So the balance should be maintained.
But, since the water level rises the hydrostatic pressure on the bottom is greater so the right side should go down.
There is another similar problem but it's not the same.
Please help. | 2017/03/16 | [
"https://physics.stackexchange.com/questions/319327",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/145936/"
] | The balance will be maintained because there is no EXTERNAL force applied on left or right side. This is because of the same reason you can't push a car while sitting in it! | If you consider everything put in the right side of balance scale as one system, only the internal forces are changed which will not affect the balance.
No external force is applied and hence the balance will be maintained. |
319,327 | 
This problem has bothered me for quite some time and I can't solve it. I have even tried to make a construction, but it sometimes tips to the left and sometimes tips to the right :).
When we submerge the body in the water the water pushes it up. That is an action. At the same time the body pushes water down. That is a reaction. So the balance should be maintained.
But, since the water level rises the hydrostatic pressure on the bottom is greater so the right side should go down.
There is another similar problem but it's not the same.
Please help. | 2017/03/16 | [
"https://physics.stackexchange.com/questions/319327",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/145936/"
] | The balance will be maintained because there is no EXTERNAL force applied on left or right side. This is because of the same reason you can't push a car while sitting in it! | Let $V$ be the volume of the hanging block, $A$ the area of the water surface, $\rho$ the density of water, and $g$ the acceleration due to gravity.
The extra hydrostatic force felt by the bottom of the container after lowering the block is
$$\Delta F = \rho gA\Delta h,$$
where $\Delta h$ is the change in water height ($\rho g \Delta h$ would be the change in hydrostatic pressure). Because water is not compressible, $A\Delta h$ must be the volume of the submerged block.
$$\Delta F = \rho g V.$$
Notice that this is exactly equal to the buoyant force on the block, so the two new forces created after the block is submerged negate each other. |
11,878,292 | i want to find out total number of android APIs (Classes and Methods) used in my android application source code. but i want to do it programmatically. can any one suggest me how can i do so??
Thanks in Advance | 2012/08/09 | [
"https://Stackoverflow.com/questions/11878292",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/631803/"
] | You can do it with [Reflections API](http://code.google.com/p/reflections/).
You can get the list of classes using the following code :
```
Reflections ref = new Reflections("package_name");
Set<Class<?>> classes = ref.getSubTypesOf(Object.class);
```
Then by using the [Class.getDeclaredMethods()](http://docs.oracle.com/javase/6/docs/api/java/lang/Class.html#getDeclaredMethods%28%29) or [Class.getMethods()](http://docs.oracle.com/javase/6/docs/api/java/lang/Class.html#getMethods%28%29) you can get the list of methods. | The eclipse metrics plugin looks promising. It is not specially designed for android but there's a chance that it will provide you with (most of) the informations you need.
**Reference**
* [project on sourceforge](http://metrics2.sourceforge.net/) |
47,678,197 | I tried asking this question before but was it was poorly stated. This is a new attempt cause I haven't solved it yet.
I have a dataset with winners, losers, date, winner\_points and loser\_points.
For each row, I want two new columns, one for the winner and one for the loser that shows how many points they have scored so far (as both winners and losers).
Example data:
```
winner <- c(1,2,3,1,2,3,1,2,3)
loser <- c(3,1,1,2,1,1,3,1,2)
date <- c("2017-10-01","2017-10-02","2017-10-03","2017-10-04","2017-10-05","2017-10-06","2017-10-07","2017-10-08","2017-10-09")
winner_points <- c(2,1,2,1,2,1,2,1,2)
loser_points <- c(1,0,1,0,1,0,1,0,1)
test_data <- data.frame(winner, loser, date = as.Date(date), winner_points, loser_points)
```
I want the output to be:
```
winner_points_sum <- c(0, 0, 1, 3, 1, 3, 5, 3, 5)
loser_points_sum <- c(0, 2, 2, 1, 4, 5, 4, 7, 4)
test_data <- data.frame(winner, loser, date = as.Date(date), winner_points, loser_points, winner_points_sum, loser_points_sum)
```
How I've solved it thus far is to do a for loop such as:
```
library(dplyr)
test_data$winner_points_sum_loop <- 0
test_data$loser_points_sum_loop <- 0
for(i in row.names(test_data)) {
test_data[i,]$winner_points_sum_loop <-
(
test_data %>%
dplyr::filter(winner == test_data[i,]$winner & date < test_data[i,]$date) %>%
dplyr::summarise(points = sum(winner_points, na.rm = TRUE))
+
test_data %>%
dplyr::filter(loser == test_data[i,]$winner & date < test_data[i,]$date) %>%
dplyr::summarise(points = sum(loser_points, na.rm = TRUE))
)
}
test_data$winner_points_sum_loop <- unlist(test_data$winner_points_sum_loop)
```
Any suggestions how to tackle this problem? The queries take quite some time when the row numbers add up. I've tried elaborating with the AVE function, I can do it for one column to sum a players point as winner but can't figure out how to add their points as loser.
[](https://i.stack.imgur.com/gEdxT.jpg) | 2017/12/06 | [
"https://Stackoverflow.com/questions/47678197",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/5434602/"
] | ```
winner <- c(1,2,3,1,2,3,1,2,3)
loser <- c(3,1,1,2,1,1,3,1,2)
date <- c("2017-10-01","2017-10-02","2017-10-03","2017-10-04","2017-10-05","2017-10-06","2017-10-07","2017-10-08","2017-10-09")
winner_points <- c(2,1,2,1,2,1,2,1,2)
loser_points <- c(1,0,1,0,1,0,1,0,1)
test_data <- data.frame(winner, loser, date = as.Date(date), winner_points, loser_points)
library(dplyr)
library(tidyr)
test_data %>%
unite(winner, winner, winner_points) %>% # unite winner columns
unite(loser, loser, loser_points) %>% # unite loser columns
gather(type, pl_pts, winner, loser, -date) %>% # reshape
separate(pl_pts, c("player","points"), convert = T) %>% # separate columns
arrange(date) %>% # order dates (in case it's not)
group_by(player) %>% # for each player
mutate(sum_points = cumsum(points) - points) %>% # get points up to that date
ungroup() %>% # forget the grouping
unite(pl_pts_sumpts, player, points, sum_points) %>% # unite columns
spread(type, pl_pts_sumpts) %>% # reshape
separate(loser, c("loser", "loser_points", "loser_points_sum"), convert = T) %>% # separate columns and give appropriate names
separate(winner, c("winner", "winner_points", "winner_points_sum"), convert = T) %>%
select(winner, loser, date, winner_points, loser_points, winner_points_sum, loser_points_sum) # select the order you prefer
# # A tibble: 9 x 7
# winner loser date winner_points loser_points winner_points_sum loser_points_sum
# * <int> <int> <date> <int> <int> <int> <int>
# 1 1 3 2017-10-01 2 1 0 0
# 2 2 1 2017-10-02 1 0 0 2
# 3 3 1 2017-10-03 2 1 1 2
# 4 1 2 2017-10-04 1 0 3 1
# 5 2 1 2017-10-05 2 1 1 4
# 6 3 1 2017-10-06 1 0 3 5
# 7 1 3 2017-10-07 2 1 5 4
# 8 2 1 2017-10-08 1 0 3 7
# 9 3 2 2017-10-09 2 1 5 4
``` | I finally understood what you want. And I took an approach of getting cumulative points of each player at each point in time and then joining it to the original `test_data` data frame.
```
winner <- c(1,2,3,1,2,3,1,2,3)
loser <- c(3,1,1,2,1,1,3,1,2)
date <- c("2017-10-01","2017-10-02","2017-10-03","2017-10-04","2017-10-05","2017-10-06","2017-10-07","2017-10-08","2017-10-09")
winner_points <- c(2,1,2,1,2,1,2,1,2)
loser_points <- c(1,0,1,0,1,0,1,0,1)
test_data <- data.frame(winner, loser, date = as.Date(date), winner_points, loser_points)
library(dplyr)
library(tidyr)
cum_points <- test_data %>%
gather(end_game_status, player_id, winner, loser) %>%
gather(which_point, how_many_points, winner_points, loser_points) %>%
filter(
(end_game_status == "winner" & which_point == "winner_points") |
(end_game_status == "loser" & which_point == "loser_points")) %>%
arrange(date = as.Date(date)) %>%
group_by(player_id) %>%
mutate(cumulative_points = cumsum(how_many_points)) %>%
mutate(cumulative_points_sofar = lag(cumulative_points, default = 0))
select(player_id, date, cumulative_points)
output <- test_data %>%
left_join(cum_points, by = c('date', 'winner' = 'player_id')) %>%
rename(winner_points_sum = cumulative_points_sofar) %>%
left_join(cum_points, by = c('date', 'loser' = 'player_id')) %>%
rename(loser_points_sum = cumulative_points_sofar)
output
``` |
47,678,197 | I tried asking this question before but was it was poorly stated. This is a new attempt cause I haven't solved it yet.
I have a dataset with winners, losers, date, winner\_points and loser\_points.
For each row, I want two new columns, one for the winner and one for the loser that shows how many points they have scored so far (as both winners and losers).
Example data:
```
winner <- c(1,2,3,1,2,3,1,2,3)
loser <- c(3,1,1,2,1,1,3,1,2)
date <- c("2017-10-01","2017-10-02","2017-10-03","2017-10-04","2017-10-05","2017-10-06","2017-10-07","2017-10-08","2017-10-09")
winner_points <- c(2,1,2,1,2,1,2,1,2)
loser_points <- c(1,0,1,0,1,0,1,0,1)
test_data <- data.frame(winner, loser, date = as.Date(date), winner_points, loser_points)
```
I want the output to be:
```
winner_points_sum <- c(0, 0, 1, 3, 1, 3, 5, 3, 5)
loser_points_sum <- c(0, 2, 2, 1, 4, 5, 4, 7, 4)
test_data <- data.frame(winner, loser, date = as.Date(date), winner_points, loser_points, winner_points_sum, loser_points_sum)
```
How I've solved it thus far is to do a for loop such as:
```
library(dplyr)
test_data$winner_points_sum_loop <- 0
test_data$loser_points_sum_loop <- 0
for(i in row.names(test_data)) {
test_data[i,]$winner_points_sum_loop <-
(
test_data %>%
dplyr::filter(winner == test_data[i,]$winner & date < test_data[i,]$date) %>%
dplyr::summarise(points = sum(winner_points, na.rm = TRUE))
+
test_data %>%
dplyr::filter(loser == test_data[i,]$winner & date < test_data[i,]$date) %>%
dplyr::summarise(points = sum(loser_points, na.rm = TRUE))
)
}
test_data$winner_points_sum_loop <- unlist(test_data$winner_points_sum_loop)
```
Any suggestions how to tackle this problem? The queries take quite some time when the row numbers add up. I've tried elaborating with the AVE function, I can do it for one column to sum a players point as winner but can't figure out how to add their points as loser.
[](https://i.stack.imgur.com/gEdxT.jpg) | 2017/12/06 | [
"https://Stackoverflow.com/questions/47678197",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/5434602/"
] | I finally understood what you want. And I took an approach of getting cumulative points of each player at each point in time and then joining it to the original `test_data` data frame.
```
winner <- c(1,2,3,1,2,3,1,2,3)
loser <- c(3,1,1,2,1,1,3,1,2)
date <- c("2017-10-01","2017-10-02","2017-10-03","2017-10-04","2017-10-05","2017-10-06","2017-10-07","2017-10-08","2017-10-09")
winner_points <- c(2,1,2,1,2,1,2,1,2)
loser_points <- c(1,0,1,0,1,0,1,0,1)
test_data <- data.frame(winner, loser, date = as.Date(date), winner_points, loser_points)
library(dplyr)
library(tidyr)
cum_points <- test_data %>%
gather(end_game_status, player_id, winner, loser) %>%
gather(which_point, how_many_points, winner_points, loser_points) %>%
filter(
(end_game_status == "winner" & which_point == "winner_points") |
(end_game_status == "loser" & which_point == "loser_points")) %>%
arrange(date = as.Date(date)) %>%
group_by(player_id) %>%
mutate(cumulative_points = cumsum(how_many_points)) %>%
mutate(cumulative_points_sofar = lag(cumulative_points, default = 0))
select(player_id, date, cumulative_points)
output <- test_data %>%
left_join(cum_points, by = c('date', 'winner' = 'player_id')) %>%
rename(winner_points_sum = cumulative_points_sofar) %>%
left_join(cum_points, by = c('date', 'loser' = 'player_id')) %>%
rename(loser_points_sum = cumulative_points_sofar)
output
``` | The difference to the [previous question of the OP](https://stackoverflow.com/q/44591583/3817004) is that the OP is now asking for the cumulative sum of points each player has scored *so far*, i.e., before the actual date. Furthermore, the sample data set now contains a `date` column which uniquely identifies each row.
So, [my previous approach](https://stackoverflow.com/a/47705647/3817004) can be used here as well, with some modifications. The solution below reshapes the data from wide to long format whereby two value variables are reshaped simultaneously, computes the cumulative sums for each player id , and finally reshapes from long back to wide format, again. In order to sum only points scored *before* the actual date, the rows are lagged by one.
It is important to note that the `winner` and `loser` columns contain the respective player ids.
```
library(data.table)
cols <- c("winner", "loser")
setDT(test_data)[
# reshape multiple value variables simultaneously from wide to long format
, melt(.SD, id.vars = "date",
measure.vars = list(cols, paste0(cols, "_points")),
value.name = c("id", "points"))][
# rename variable column
, variable := forcats::lvls_revalue(variable, cols)][
# order by date and cumulate the lagged points by id
order(date), points_sum := cumsum(shift(points, fill = 0)), by = id][
# reshape multiple value variables simultaneously from long to wide format
, dcast(.SD, date ~ variable, value.var = c("id", "points", "points_sum"))]
```
>
>
> ```
> date id_winner id_loser points_winner points_loser points_sum_winner points_sum_loser
> 1: 2017-10-01 1 3 2 1 0 0
> 2: 2017-10-02 2 1 1 0 0 2
> 3: 2017-10-03 3 1 2 1 1 2
> 4: 2017-10-04 1 2 1 0 3 1
> 5: 2017-10-05 2 1 2 1 1 4
> 6: 2017-10-06 3 1 1 0 3 5
> 7: 2017-10-07 1 3 2 1 5 4
> 8: 2017-10-08 2 1 1 0 3 7
> 9: 2017-10-09 3 2 2 1 5 4
>
> ```
>
> |
47,678,197 | I tried asking this question before but was it was poorly stated. This is a new attempt cause I haven't solved it yet.
I have a dataset with winners, losers, date, winner\_points and loser\_points.
For each row, I want two new columns, one for the winner and one for the loser that shows how many points they have scored so far (as both winners and losers).
Example data:
```
winner <- c(1,2,3,1,2,3,1,2,3)
loser <- c(3,1,1,2,1,1,3,1,2)
date <- c("2017-10-01","2017-10-02","2017-10-03","2017-10-04","2017-10-05","2017-10-06","2017-10-07","2017-10-08","2017-10-09")
winner_points <- c(2,1,2,1,2,1,2,1,2)
loser_points <- c(1,0,1,0,1,0,1,0,1)
test_data <- data.frame(winner, loser, date = as.Date(date), winner_points, loser_points)
```
I want the output to be:
```
winner_points_sum <- c(0, 0, 1, 3, 1, 3, 5, 3, 5)
loser_points_sum <- c(0, 2, 2, 1, 4, 5, 4, 7, 4)
test_data <- data.frame(winner, loser, date = as.Date(date), winner_points, loser_points, winner_points_sum, loser_points_sum)
```
How I've solved it thus far is to do a for loop such as:
```
library(dplyr)
test_data$winner_points_sum_loop <- 0
test_data$loser_points_sum_loop <- 0
for(i in row.names(test_data)) {
test_data[i,]$winner_points_sum_loop <-
(
test_data %>%
dplyr::filter(winner == test_data[i,]$winner & date < test_data[i,]$date) %>%
dplyr::summarise(points = sum(winner_points, na.rm = TRUE))
+
test_data %>%
dplyr::filter(loser == test_data[i,]$winner & date < test_data[i,]$date) %>%
dplyr::summarise(points = sum(loser_points, na.rm = TRUE))
)
}
test_data$winner_points_sum_loop <- unlist(test_data$winner_points_sum_loop)
```
Any suggestions how to tackle this problem? The queries take quite some time when the row numbers add up. I've tried elaborating with the AVE function, I can do it for one column to sum a players point as winner but can't figure out how to add their points as loser.
[](https://i.stack.imgur.com/gEdxT.jpg) | 2017/12/06 | [
"https://Stackoverflow.com/questions/47678197",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/5434602/"
] | ```
winner <- c(1,2,3,1,2,3,1,2,3)
loser <- c(3,1,1,2,1,1,3,1,2)
date <- c("2017-10-01","2017-10-02","2017-10-03","2017-10-04","2017-10-05","2017-10-06","2017-10-07","2017-10-08","2017-10-09")
winner_points <- c(2,1,2,1,2,1,2,1,2)
loser_points <- c(1,0,1,0,1,0,1,0,1)
test_data <- data.frame(winner, loser, date = as.Date(date), winner_points, loser_points)
library(dplyr)
library(tidyr)
test_data %>%
unite(winner, winner, winner_points) %>% # unite winner columns
unite(loser, loser, loser_points) %>% # unite loser columns
gather(type, pl_pts, winner, loser, -date) %>% # reshape
separate(pl_pts, c("player","points"), convert = T) %>% # separate columns
arrange(date) %>% # order dates (in case it's not)
group_by(player) %>% # for each player
mutate(sum_points = cumsum(points) - points) %>% # get points up to that date
ungroup() %>% # forget the grouping
unite(pl_pts_sumpts, player, points, sum_points) %>% # unite columns
spread(type, pl_pts_sumpts) %>% # reshape
separate(loser, c("loser", "loser_points", "loser_points_sum"), convert = T) %>% # separate columns and give appropriate names
separate(winner, c("winner", "winner_points", "winner_points_sum"), convert = T) %>%
select(winner, loser, date, winner_points, loser_points, winner_points_sum, loser_points_sum) # select the order you prefer
# # A tibble: 9 x 7
# winner loser date winner_points loser_points winner_points_sum loser_points_sum
# * <int> <int> <date> <int> <int> <int> <int>
# 1 1 3 2017-10-01 2 1 0 0
# 2 2 1 2017-10-02 1 0 0 2
# 3 3 1 2017-10-03 2 1 1 2
# 4 1 2 2017-10-04 1 0 3 1
# 5 2 1 2017-10-05 2 1 1 4
# 6 3 1 2017-10-06 1 0 3 5
# 7 1 3 2017-10-07 2 1 5 4
# 8 2 1 2017-10-08 1 0 3 7
# 9 3 2 2017-10-09 2 1 5 4
``` | The difference to the [previous question of the OP](https://stackoverflow.com/q/44591583/3817004) is that the OP is now asking for the cumulative sum of points each player has scored *so far*, i.e., before the actual date. Furthermore, the sample data set now contains a `date` column which uniquely identifies each row.
So, [my previous approach](https://stackoverflow.com/a/47705647/3817004) can be used here as well, with some modifications. The solution below reshapes the data from wide to long format whereby two value variables are reshaped simultaneously, computes the cumulative sums for each player id , and finally reshapes from long back to wide format, again. In order to sum only points scored *before* the actual date, the rows are lagged by one.
It is important to note that the `winner` and `loser` columns contain the respective player ids.
```
library(data.table)
cols <- c("winner", "loser")
setDT(test_data)[
# reshape multiple value variables simultaneously from wide to long format
, melt(.SD, id.vars = "date",
measure.vars = list(cols, paste0(cols, "_points")),
value.name = c("id", "points"))][
# rename variable column
, variable := forcats::lvls_revalue(variable, cols)][
# order by date and cumulate the lagged points by id
order(date), points_sum := cumsum(shift(points, fill = 0)), by = id][
# reshape multiple value variables simultaneously from long to wide format
, dcast(.SD, date ~ variable, value.var = c("id", "points", "points_sum"))]
```
>
>
> ```
> date id_winner id_loser points_winner points_loser points_sum_winner points_sum_loser
> 1: 2017-10-01 1 3 2 1 0 0
> 2: 2017-10-02 2 1 1 0 0 2
> 3: 2017-10-03 3 1 2 1 1 2
> 4: 2017-10-04 1 2 1 0 3 1
> 5: 2017-10-05 2 1 2 1 1 4
> 6: 2017-10-06 3 1 1 0 3 5
> 7: 2017-10-07 1 3 2 1 5 4
> 8: 2017-10-08 2 1 1 0 3 7
> 9: 2017-10-09 3 2 2 1 5 4
>
> ```
>
> |
47,902,057 | I have a text as follows.
```
mytext = "This is AVGs_ABB and NMN_ABB and most importantly GFD_ABB This is so important that you have to CLEAN the lab everyday"
```
I want to convert it to lowercase, except the words that has `_ABB` in it.
So, my output should look as follows.
```
mytext = "this is AVGs_ABB and NMN_ABB and most importantly GFD_ABB this is so important that you have to clean the lab everyday"
```
My current code is as follows.
```
splits = mytext.split()
newtext = []
for item in splits:
if not '_ABB' in item:
item = item.lower()
newtext.append(item)
else:
newtext.append(item)
```
However, I want to know if there is any easy way of doing this, possibly in one line? | 2017/12/20 | [
"https://Stackoverflow.com/questions/47902057",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/-1/"
] | You can use a one liner splitting the string into words, check the words with `str.endswith()` and then join the words back together:
```
' '.join(w if w.endswith('_ABB') else w.lower() for w in mytext.split())
# 'this is AVGs_ABB and NMN_ABB and most importantly GFD_ABB this is so important that you have to clean the lab everyday'
```
Of course use the `in` operator rather than `str.endswith()` if `'_ABB'` can actually occur anywhere in the word and not just at the end. | Extended *regex* approach:
```
import re
mytext = "This is AVGs_ABB and NMN_ABB and most importantly GFD_ABB This is so important that you have to CLEAN the lab everyday"
result = re.sub(r'\b((?!_ABB)\S)+\b', lambda m: m.group().lower(), mytext)
print(result)
```
The output:
```
this is AVGs_ABB and NMN_ABB and most importantly GFD_ABB this is so important that you have to clean the lab everyday
```
---
Details:
* `\b` - word boundary
* `(?!_ABB)` - lookahead negative assertion, ensures that the given pattern will not match
* `\S` - non-whitespace character
* `\b((?!_ABB)\S)+\b` - the whole pattern matches a word NOT containing substring `_ABB` |
47,902,057 | I have a text as follows.
```
mytext = "This is AVGs_ABB and NMN_ABB and most importantly GFD_ABB This is so important that you have to CLEAN the lab everyday"
```
I want to convert it to lowercase, except the words that has `_ABB` in it.
So, my output should look as follows.
```
mytext = "this is AVGs_ABB and NMN_ABB and most importantly GFD_ABB this is so important that you have to clean the lab everyday"
```
My current code is as follows.
```
splits = mytext.split()
newtext = []
for item in splits:
if not '_ABB' in item:
item = item.lower()
newtext.append(item)
else:
newtext.append(item)
```
However, I want to know if there is any easy way of doing this, possibly in one line? | 2017/12/20 | [
"https://Stackoverflow.com/questions/47902057",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/-1/"
] | You can use a one liner splitting the string into words, check the words with `str.endswith()` and then join the words back together:
```
' '.join(w if w.endswith('_ABB') else w.lower() for w in mytext.split())
# 'this is AVGs_ABB and NMN_ABB and most importantly GFD_ABB this is so important that you have to clean the lab everyday'
```
Of course use the `in` operator rather than `str.endswith()` if `'_ABB'` can actually occur anywhere in the word and not just at the end. | Here is another possible(not elegant) one-liner:
```
mytext = "This is AVGs_ABB and NMN_ABB and most importantly GFD_ABB This is so important that you have to CLEAN the lab everyday"
print(' '.join(map(lambda x : x if '_ABB' in x else x.lower(), mytext.split())))
```
Which Outputs:
```
this is AVGs_ABB and NMN_ABB and most importantly GFD_ABB this is so important that you have to clean the lab everyday
```
**Note:** This assumes that your text will only seperate the words by spaces, so `split()` suffices here. If your text includes punctuation such as`",!."`, you will need to use regex instead to split up the words. |
47,902,057 | I have a text as follows.
```
mytext = "This is AVGs_ABB and NMN_ABB and most importantly GFD_ABB This is so important that you have to CLEAN the lab everyday"
```
I want to convert it to lowercase, except the words that has `_ABB` in it.
So, my output should look as follows.
```
mytext = "this is AVGs_ABB and NMN_ABB and most importantly GFD_ABB this is so important that you have to clean the lab everyday"
```
My current code is as follows.
```
splits = mytext.split()
newtext = []
for item in splits:
if not '_ABB' in item:
item = item.lower()
newtext.append(item)
else:
newtext.append(item)
```
However, I want to know if there is any easy way of doing this, possibly in one line? | 2017/12/20 | [
"https://Stackoverflow.com/questions/47902057",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/-1/"
] | Extended *regex* approach:
```
import re
mytext = "This is AVGs_ABB and NMN_ABB and most importantly GFD_ABB This is so important that you have to CLEAN the lab everyday"
result = re.sub(r'\b((?!_ABB)\S)+\b', lambda m: m.group().lower(), mytext)
print(result)
```
The output:
```
this is AVGs_ABB and NMN_ABB and most importantly GFD_ABB this is so important that you have to clean the lab everyday
```
---
Details:
* `\b` - word boundary
* `(?!_ABB)` - lookahead negative assertion, ensures that the given pattern will not match
* `\S` - non-whitespace character
* `\b((?!_ABB)\S)+\b` - the whole pattern matches a word NOT containing substring `_ABB` | Here is another possible(not elegant) one-liner:
```
mytext = "This is AVGs_ABB and NMN_ABB and most importantly GFD_ABB This is so important that you have to CLEAN the lab everyday"
print(' '.join(map(lambda x : x if '_ABB' in x else x.lower(), mytext.split())))
```
Which Outputs:
```
this is AVGs_ABB and NMN_ABB and most importantly GFD_ABB this is so important that you have to clean the lab everyday
```
**Note:** This assumes that your text will only seperate the words by spaces, so `split()` suffices here. If your text includes punctuation such as`",!."`, you will need to use regex instead to split up the words. |
17,006,512 | I have a simple table layout, in the one of the row, I have time for sun rise in a text view and I am trying to have sun with purple colour for the row as background. How can I achieve this? I tried creating an image 1000px x 500px with sun and purple background, However, it does not look good on different screen sizes. What is the solution for this?
Here is an image of what I am trying to achieve  | 2013/06/09 | [
"https://Stackoverflow.com/questions/17006512",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/2122179/"
] | You can set it programmatically by
```
[textField setSecureTextEntry:YES];
```
or in IB (secured checkbox at the bottom)
 | You could also try simply implementing your own "secure text field".
Simply create a normal, non-secure text field, and link it's "Editing Changed" action with a method in your view controller.
Then within that method you can take the new characters every time the text is changed, and add them to a private NSString property, and then set the textField's .text property to a string with just asterisks in it (or any other character if you prefer).
**Update:** as noted by *hayesk* below, this solution is no longer ideal, as the introduction of third-party keyboards exposes input on any non-secure text fields to the third-party application, risking them collecting that information, and/or adding it to the autocorrect database. |
59,938,330 | I'm using a jsonb field in my Rails application and have installed the [gem attr\_json](https://github.com/jrochkind/attr_json). Is there a way to receive the defined json\_attributes programmatically? With a "normal" rails attribute, I would just do @instance.attribute\_names. But with attr\_json is there any way how to have the json\_attributes returned?
```
class Vehicle < Item
include AttrJson::Record
attr_json :licence_plate, :string, container_attribute: "custom_attributes_indexed"
attr_json :brand, :string, container_attribute: "custom_attributes_indexed"
attr_json :serial_number, :string, container_attribute: "custom_attributes_indexed"
attr_json :inventory_number, :string, container_attribute: "custom_attributes_indexed"
end
```
For this code I would like to do something like @vehicle.json\_attribute\_names and have the following returned
```
["licence_plate", "brand", "serial_number", "inventory_number"]
``` | 2020/01/27 | [
"https://Stackoverflow.com/questions/59938330",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/3748376/"
] | I think you should clear your previous model inside loop so you could use this function which is keras.backend.clear\_session().From <https://keras.io/backend/>:
This will be solved your problem. | From a very simplistic point of view, the data is fed in sequentially, which suggests that at the very least, it's possible for the data order to have an effect on the output. If the order doesn't matter, randomization certainly won't hurt. If the order does matter, randomization will help to smooth out those random effects so that they don't become systematic bias. In short, randomization is cheap and never hurts, and will often minimize data-ordering effects.
In other words, when you feed your neural network with different datasets, your model can get biased towards the latest dataset it was trained on.
You should always make sure that your are randomly sampling from all datasets you have. |
5,578,250 | As I am writing my first grails webflow I am asking myself if there is anyy tool or script what can visualize the flow?
Result can be a state diagram or some data to render in a graph tool like graphviz. | 2011/04/07 | [
"https://Stackoverflow.com/questions/5578250",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/172590/"
] | There's no tool around currently that will do this for you I'm afraid. I've implemented something myself before, but this was very simple and was not automated in any way. It was a simple template where the model was a step number:
```
<g:render template="flowVisualiser" model="[step: 2]" />
```
You would have to put this in every view of the webflow, changing the number for whatever step it was. The template itself just had a row of images for each of the steps, and there was some gsp logic in the style of each image so that if the model passed in was step 2 (for instance) or above then this particular image would have opacity 1:
```
<li>
<div class="${step >= 2 ? 'step-completed' : 'step-todo'}">
<img src="${resource(dir:'images',file:'2.png')}" />
<h4>Do this step</h4>
</div>
</li>
...
```
I know it's not fancy and it's a bit of manual labor but it worked just fine for me :) | As far as I know there's only 2 plugin for Grails which do visualization, but only build a class-diagram, They are [Class diagram plugin](http://grails.org/plugin/class-diagram/) and [Create Domain UML](http://www.grails.org/plugin/create-domain-uml).
You can have a look at [this page](http://www.grails.org/plugin/category/all) for a quick review about all current Grails plugin. |
5,578,250 | As I am writing my first grails webflow I am asking myself if there is anyy tool or script what can visualize the flow?
Result can be a state diagram or some data to render in a graph tool like graphviz. | 2011/04/07 | [
"https://Stackoverflow.com/questions/5578250",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/172590/"
] | There's no tool around currently that will do this for you I'm afraid. I've implemented something myself before, but this was very simple and was not automated in any way. It was a simple template where the model was a step number:
```
<g:render template="flowVisualiser" model="[step: 2]" />
```
You would have to put this in every view of the webflow, changing the number for whatever step it was. The template itself just had a row of images for each of the steps, and there was some gsp logic in the style of each image so that if the model passed in was step 2 (for instance) or above then this particular image would have opacity 1:
```
<li>
<div class="${step >= 2 ? 'step-completed' : 'step-todo'}">
<img src="${resource(dir:'images',file:'2.png')}" />
<h4>Do this step</h4>
</div>
</li>
...
```
I know it's not fancy and it's a bit of manual labor but it worked just fine for me :) | probably this could be a solution for all people using intellij: <http://www.slideshare.net/gr8conf/gr8conf-2011-grails-webflow>
Slide 25 |
26,377,384 | I want adding background image with css but it did not work.Browser show me a blank page.
my application.css
```
home-body {
background-image: url('/home.jpg') no-repeat center center fixed;
-webkit-background-size: cover;
-moz-background-size: cover;
-o-background-size: cover;
background-size: cover;
}
```
file home.jpg located in a directory /public/home.jpg.
How fix? | 2014/10/15 | [
"https://Stackoverflow.com/questions/26377384",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/4059461/"
] | Please use this code. Use background instead of background-image and make sure that you have inserted the correct image path in url().
```
html, body {
margin: 0;
padding: 0;
height: 100%;
width: 100%;
}
.home-body {
background: url('/home.jpg') no-repeat center center fixed;
-webkit-background-size: cover;
-moz-background-size: cover;
-o-background-size: cover;
background-size: cover;
}
``` | very easy like this....
```
.play{
background: url("media_element/play.png") center center no-repeat;
position : absolute;
display:block;
top:20%;
width:50px;
margin:0 auto;
left:0px;
right:0px;
z-index:100
}
``` |
26,377,384 | I want adding background image with css but it did not work.Browser show me a blank page.
my application.css
```
home-body {
background-image: url('/home.jpg') no-repeat center center fixed;
-webkit-background-size: cover;
-moz-background-size: cover;
-o-background-size: cover;
background-size: cover;
}
```
file home.jpg located in a directory /public/home.jpg.
How fix? | 2014/10/15 | [
"https://Stackoverflow.com/questions/26377384",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/4059461/"
] | Please use this code. Use background instead of background-image and make sure that you have inserted the correct image path in url().
```
html, body {
margin: 0;
padding: 0;
height: 100%;
width: 100%;
}
.home-body {
background: url('/home.jpg') no-repeat center center fixed;
-webkit-background-size: cover;
-moz-background-size: cover;
-o-background-size: cover;
background-size: cover;
}
``` | ```
body {
background-image: url('img-url');
background-size: cover;
background-repeat:no-repeat
}
``` |
26,377,384 | I want adding background image with css but it did not work.Browser show me a blank page.
my application.css
```
home-body {
background-image: url('/home.jpg') no-repeat center center fixed;
-webkit-background-size: cover;
-moz-background-size: cover;
-o-background-size: cover;
background-size: cover;
}
```
file home.jpg located in a directory /public/home.jpg.
How fix? | 2014/10/15 | [
"https://Stackoverflow.com/questions/26377384",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/4059461/"
] | If you are using an external CSS file... make sure to link the image file relative to the CSS file. For instance
`-ROOT
-css
-file.css
-background.jpg
-index.html`
you would need:
`background("../background.jpg");`
because ".." takes you up one directory :) | very easy like this....
```
.play{
background: url("media_element/play.png") center center no-repeat;
position : absolute;
display:block;
top:20%;
width:50px;
margin:0 auto;
left:0px;
right:0px;
z-index:100
}
``` |
26,377,384 | I want adding background image with css but it did not work.Browser show me a blank page.
my application.css
```
home-body {
background-image: url('/home.jpg') no-repeat center center fixed;
-webkit-background-size: cover;
-moz-background-size: cover;
-o-background-size: cover;
background-size: cover;
}
```
file home.jpg located in a directory /public/home.jpg.
How fix? | 2014/10/15 | [
"https://Stackoverflow.com/questions/26377384",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/4059461/"
] | If you are using an external CSS file... make sure to link the image file relative to the CSS file. For instance
`-ROOT
-css
-file.css
-background.jpg
-index.html`
you would need:
`background("../background.jpg");`
because ".." takes you up one directory :) | ```
body {
background-image: url('img-url');
background-size: cover;
background-repeat:no-repeat
}
``` |
26,377,384 | I want adding background image with css but it did not work.Browser show me a blank page.
my application.css
```
home-body {
background-image: url('/home.jpg') no-repeat center center fixed;
-webkit-background-size: cover;
-moz-background-size: cover;
-o-background-size: cover;
background-size: cover;
}
```
file home.jpg located in a directory /public/home.jpg.
How fix? | 2014/10/15 | [
"https://Stackoverflow.com/questions/26377384",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/4059461/"
] | it may be caused by 3 problem
1- home-body is not a tag of html.so it should be id or class name of a tag.so you should use `.home-body` for class name and `#home-body` for id name.
2- you do not address the background image correctly.if you want to make sure, give the url as an absolute path to your image like `http://yoursiteUrl/public/image/image.png`
3- your css file is not loaded on your page.try to make sure it is loaded on your site correctly if it is loaded then the problem is first or the second part mentioned here. | very easy like this....
```
.play{
background: url("media_element/play.png") center center no-repeat;
position : absolute;
display:block;
top:20%;
width:50px;
margin:0 auto;
left:0px;
right:0px;
z-index:100
}
``` |
26,377,384 | I want adding background image with css but it did not work.Browser show me a blank page.
my application.css
```
home-body {
background-image: url('/home.jpg') no-repeat center center fixed;
-webkit-background-size: cover;
-moz-background-size: cover;
-o-background-size: cover;
background-size: cover;
}
```
file home.jpg located in a directory /public/home.jpg.
How fix? | 2014/10/15 | [
"https://Stackoverflow.com/questions/26377384",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/4059461/"
] | it may be caused by 3 problem
1- home-body is not a tag of html.so it should be id or class name of a tag.so you should use `.home-body` for class name and `#home-body` for id name.
2- you do not address the background image correctly.if you want to make sure, give the url as an absolute path to your image like `http://yoursiteUrl/public/image/image.png`
3- your css file is not loaded on your page.try to make sure it is loaded on your site correctly if it is loaded then the problem is first or the second part mentioned here. | ```
body {
background-image: url('img-url');
background-size: cover;
background-repeat:no-repeat
}
``` |
1,817,508 | I have a vector class that has addition, multiplication, subtraction, division, etc operators. I'm trying to optimize my program (which does a lot of vector operations) and I'm realizing that about 50% of the time spent is in constructing and destructing vectors. I understand that this is because every time I call a non-compound mathematical operator for a vector, a new vector is constructed. Is there a way to prevent this without using compound operators or expanding vector operations?
If I have:
```
Vector a = Vector(x, y, z);
Vector b = Vector(a, b, c);
Vector c = a + b;
```
I can't use += because c is a completely new vector. I know I can speed it up with this:
```
c.x = a.x + b.x;
c.y = a.y + b.y;
c.z = a.z + b.z;
```
but that doesn't seem as clean as just using an operator. | 2009/11/30 | [
"https://Stackoverflow.com/questions/1817508",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/217546/"
] | >
> I understand that this is because
> every time I call a non-compound
> mathematical operator for a vector, a
> new vector is constructed. Is there a
> way to prevent this without using
> compound operators or expanding vector
> operations?
>
>
>
Well, the nature of adding two things together to produce a third thing *requires* you to construct a third thing...so how is what you're asking even logically possible?
That being said, if you're concerned about the temporaries created by using the addition operator, these may be optimized out by the compiler if your compiler supports return value optimization. Alternatively, if your compiler doesn't support this and you really want to cut back on temporaries but keep the `+` operator, you may want to look into emulating C++0x move semantics, and provide your vector with a rvalue move constructor, which will be invoked when it returns a temporary by value. See the Section titled "Moving Objects" in [this article](http://www.ddj.com/cpp/184403806) for information on implementing move semantics in C++03. Once C++0x comes out, you can just replace these hacks with real move constructors using the `&&` operator for rvalue references. | Make sure you have optimizations turned on and that your compiler is applying [RVO](http://en.wikipedia.org/wiki/Return_value_optimization), which is designed for exactly this situation (but not required to be used). (You may have to use a form of NRVO in your op+ implementation, example below, which helps the compiler recognize and apply RVO.) Also, have you looked at [blitz++](http://www.oonumerics.org/blitz/)?
```
Vector operator+(Vector const& a, Vector const& b) {
Vector nrvo;
// or: Vector nrvo (ctor, parameters, here);
//...
return nrvo;
}
```
---
There are other alternatives too, such as doing an explicit copy and then using op+=, which serves in a situation where RVO doesn't apply:
```
Vector c; // created somewhere else, and we want to assign to it
// instead of create it "in-place" as RVO does
Vector a, b;
// instead of:
//c = a + b
// use:
c = a;
c += b;
```
This can be achieved with [expression templates](http://en.wikipedia.org/wiki/Expression_templates), like blitz++ uses, without changing your syntax from `c = a + b`. |
1,817,508 | I have a vector class that has addition, multiplication, subtraction, division, etc operators. I'm trying to optimize my program (which does a lot of vector operations) and I'm realizing that about 50% of the time spent is in constructing and destructing vectors. I understand that this is because every time I call a non-compound mathematical operator for a vector, a new vector is constructed. Is there a way to prevent this without using compound operators or expanding vector operations?
If I have:
```
Vector a = Vector(x, y, z);
Vector b = Vector(a, b, c);
Vector c = a + b;
```
I can't use += because c is a completely new vector. I know I can speed it up with this:
```
c.x = a.x + b.x;
c.y = a.y + b.y;
c.z = a.z + b.z;
```
but that doesn't seem as clean as just using an operator. | 2009/11/30 | [
"https://Stackoverflow.com/questions/1817508",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/217546/"
] | >
> I understand that this is because
> every time I call a non-compound
> mathematical operator for a vector, a
> new vector is constructed. Is there a
> way to prevent this without using
> compound operators or expanding vector
> operations?
>
>
>
Well, the nature of adding two things together to produce a third thing *requires* you to construct a third thing...so how is what you're asking even logically possible?
That being said, if you're concerned about the temporaries created by using the addition operator, these may be optimized out by the compiler if your compiler supports return value optimization. Alternatively, if your compiler doesn't support this and you really want to cut back on temporaries but keep the `+` operator, you may want to look into emulating C++0x move semantics, and provide your vector with a rvalue move constructor, which will be invoked when it returns a temporary by value. See the Section titled "Moving Objects" in [this article](http://www.ddj.com/cpp/184403806) for information on implementing move semantics in C++03. Once C++0x comes out, you can just replace these hacks with real move constructors using the `&&` operator for rvalue references. | Whoa there. Your code is totally inefficient:
```
Vector a = Vector(x, y, z);
Vector b = Vector(a, b, c);
```
That's just inefficient. What you want to write is
```
Vector a(x, y, z);
Vector b(a, b, c);
``` |
234,979 | I maintain a set of command line bioinformatics tools which we distribute as source and binaries for Linux, Windows, and OS X. Currently the binary distribution for OS X is just a zip file containing directories for the binaries and the documentation. Our install guide directs the user to unzip the archive, copy the binaries to the desired location, and update their PATH to point to the binaries. That's fine for the command line savvy users, but some users have never heard of /usr/local/bin let alone PATH. We'd love to have an installer that's in more of the OS X idiom.
Creating an application bundle doesn't seem to do the trick because our tools are strictly command line and they'll need a terminal session to use them. It seems like we could have used PackageMaker to create an installer, but that's now deprecated.
Is there a current standard installer for command line tools on OS X, preferably one with CPACK support? | 2016/04/14 | [
"https://apple.stackexchange.com/questions/234979",
"https://apple.stackexchange.com",
"https://apple.stackexchange.com/users/7226/"
] | The standard package format is the "pkg" format. It's not often used for applications, but it's fine for a terminal-only utility.
* My go-to tool for creating packages is called [Packages](http://s.sudre.free.fr/Software/Packages/about.html).
* I haven't used it myself, but it looks like CMake [supports PackageMaker](https://cmake.org/Wiki/CMake:CPackPackageGenerators#PackageMaker_.28OSX_only.29), which is a third party tool for creating OS X packages.
* There's also the built-in [pkgbuild](https://developer.apple.com/library/mac/documentation/Darwin/Reference/ManPages/man1/pkgbuild.1.html#//apple_ref/doc/man/1/pkgbuild) utility.
Just make sure you don't touch anything outside the [standard paths](https://support.apple.com/en-au/HT204899) (`/Library`, `/Applications`, or `/usr/local/`) and you'll be fine. | You may want to have a look at **[EPM](http://www.msweet.org/projects.php?Z2)**, the Easy Package Manager.
It can package Mac OS X `pkg` as well as RedHat `RPM`, Debian `deb` and then some more package formats -- all from the same source files, immediately after the build step.
It was originally written by Michael Sweet, the author of CUPS (who now works for Apple), and is still maintained by him.
The documentation is here:
* <http://www.msweet.org/documentation/project2/EPM.html>
EPM is available via MacPorts (albeit in an older version, v4.1, whereas the current one is v4.3).
To use it in your Makefile, it is as easy as adding an additional target like this:
```
osx:
epm -f osx -v -s doc/epmlogo.tif $(MY_PROJECT)
```
---
Of course, you can also use it standalone (not from the Makefile) to package your software.
It requires you to create a list of files with their paths, permissions and some other meta info which should be packaged. |
13,358,503 | a gem intends to support gems `a` or `b` as alternatives for a functionality.
In code I check with `defined?(A)` if I fall back to `b` that's fine.
But as a gem developer how to specify these dependencies?
1) what do I put in the Gemfile.
```
group :development, :test do
gem 'a', :require => false
gem 'b', :require => false
end
```
This allows `Bundle.require(:test)` not to auto-require a,b?
2) How can explicitly require `a` and `b` separately to mimic (or mock) the scenario when we fall back to `b` in my tests?
3) Also how do I specify that either `a` or `b` is prerequisite for the gem.
thanks | 2012/11/13 | [
"https://Stackoverflow.com/questions/13358503",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/641672/"
] | Don't include the `a` gem in your dependencies, but `require` it anyway. If that fails, it will raise `LoadError`, from which you can rescue.
```
begin
require 'a'
rescue LoadError
# The 'a' gem is not installed
require 'b'
end
```
---
I believe this is the best way to use and test this setup:
1. Define an interface for your backend and allow a custom implementation to be easily plugged in.
```
module YourGem
class << self
attr_accessor :backend
def do_something_awesome
backend.do_something_awesome
end
end
end
```
2. Implement the `a` and `b` backends.
```
# your_gem/backends/a.rb
require 'a'
module YourGem::Backends::A
def self.do_something_awesome
# Do it
end
end
# your_gem/backends/b.rb
require 'b'
module YourGem::Backends::B
def self.do_something_awesome
# Do it
end
end
```
3. Set the one you want to use.
```
begin
require 'your_gem/backends/a'
Gem.backend = YourGem::Backends::A
rescue LoadError
require 'your_gem/backends/b'
Gem.backend = YourGem::Backends::B
end
```
This will use `YourGem::Backend::A` even if `b` is installed.
4. Before testing, make sure both `a` and `b` gems are installed, `require` both backends in the test code, run the tests with one backend, then run the tests again with the other backend. | I got this same question a while ago. My solution was to think that the developer should specify this behavior. I would not specify it on the gem, but on the wiki. I would recommend you to document it clearly that the developer need to define one of the dependencies.
To make it better, you can make a check on initialization of the gem, looking for the dependencies, if none can be found, just raise a runtime exception or if you prefer, your own exception. =) |
18,939,332 | Does anyone know what Facebook uses for their blurred toolbar?
Now, I **KNOW** there are already countless threads about iOS 7 blur. They all come to these same solutions:
1. Use a UIToolbar with translucent set to YES, and then set its barTintColor property. The problem with this approach is that it significantly increases the lightness of the color. This is the approach that [AMBlurView](https://github.com/JagCesar/iOS-blur) uses. The nav bar in the Facebook app remains dark blue even when it's above white content. (with AMBlurView it becomes pastel blue)
2. Render the underlying view's in a graphic context, then blur that context, output it as a UIImage and use that as background view, repeat 30 times per second. (which hurts performance pretty bad). This is the approach that [FXBlurView](https://github.com/nicklockwood/FXBlurView) uses. It doesn't seem like Facebook is using that either.
I've read at length in the Apple Dev Forums and it seems like this is a technical challenge even for Apple engineers. With Facebook nailing the real-time blur with something else than the two approaches I described. Any idea? | 2013/09/22 | [
"https://Stackoverflow.com/questions/18939332",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/87158/"
] | Apparently the trick here is to insert the translucent layer as a sublayer of the navigation bar. I take no credit for finding this, and the following snippet has been taken [**from this gist**](https://gist.github.com/alanzeino/6619253).
```
UIColor *barColour = [UIColor colorWithRed:0.13f green:0.14f blue:0.15f alpha:1.00f];
UIView *colourView = [[UIView alloc] initWithFrame:CGRectMake(0.f, -20.f, 320.f, 64.f)];
colourView.opaque = NO;
colourView.alpha = .7f;
colourView.backgroundColor = barColour;
self.navigationBar.barTintColor = barColour;
[self.navigationBar.layer insertSublayer:colourView.layer atIndex:1];
``` | I couldn't get the desired results unless I have added the following lines to the answer above:
```
[self.navigationBar setBackgroundImage:[UIImage new]
forBarMetrics:UIBarMetricsDefault];
self.navigationBar.shadowImage = [UIImage new];
self.navigationBar.translucent = YES;
```
Here is the full code
```
[self.navigationBar setBackgroundImage:[UIImage new]
forBarMetrics:UIBarMetricsDefault];
self.navigationBar.shadowImage = [UIImage new];
self.navigationBar.translucent = YES;
UIColor *barColour = [UIColor colorWithRed:0.13f green:0.14f blue:0.15f alpha:1.00f];
UIView *colourView = [[UIView alloc] initWithFrame:CGRectMake(0.f, -20.f, 320.f, 64.f)];
colourView.opaque = NO;
colourView.alpha = .7f;
colourView.backgroundColor = barColour;
self.navigationBar.barTintColor = barColour;
[self.navigationBar.layer insertSublayer:colourView.layer atIndex:1];
``` |
54,558,029 | Here is my original df:
```
my_df_1 <- data.frame(col_1 = c(rep('a',5), rep('b',5), rep('c', 5)),
col_2 = c(rep('x',3), rep('y', 9), rep('x', 3)))
```
I would like to group by `col_1` and return 1 if `col_2` for given group contains `x`, and 0 if not.
Here is how final result is supposed to look:
```
my_df_2 <- data.frame(col_1 = c(rep('a',5), rep('b',5), rep('c', 5)),
col_2 = c(rep('x',3), rep('y', 9), rep('x', 3)),
col_3 = c(rep(1,5), rep(0,5), rep(1, 5)))
```
I would prefer to get it done with `dplyr`, if possible. This is kind of `count if` predicate, but cannot find it. | 2019/02/06 | [
"https://Stackoverflow.com/questions/54558029",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/1700890/"
] | What about this?
```
do <- as.data.frame(do.call(rbind, lapply(my.stuff, as.vector)))
do <- cbind(my.var=rownames(do), do)
do[do == "NULL"] <- NA
```
***Result***
```
> do
my.var my.col1 my.col2 my.col3 my.col4
AA AA 1 4 NA NA
BB BB NA NA NA NA
CC CC 13 8 2 10
DD DD NA NA -5 7
```
### *Edit:*
If we don't want lists as column objects as @akrun reasonably suggests, we could do it this way:
```
u <- as.character(unlist(my.stuff, recursive=FALSE))
u[u == "NULL"] <- NA
do <- matrix(as.integer(u), nrow=4, byrow=TRUE,
dimnames=list(NULL, names(my.stuff[[1]])))
do <- data.frame(my.var=names(my.stuff), do, stringsAsFactors=FALSE)
```
***Test:***
```none
> all.equal(str(do), str(desired.object))
'data.frame': 4 obs. of 5 variables:
$ my.var : chr "AA" "BB" "CC" "DD"
$ my.col1: int 1 NA 13 NA
$ my.col2: int 4 NA 8 NA
$ my.col3: int NA NA 2 -5
$ my.col4: int NA NA 10 7
'data.frame': 4 obs. of 5 variables:
$ my.var : chr "AA" "BB" "CC" "DD"
$ my.col1: int 1 NA 13 NA
$ my.col2: int 4 NA 8 NA
$ my.col3: int NA NA 2 -5
$ my.col4: int NA NA 10 7
[1] TRUE
``` | We can use a recursive `map`
```
library(tidyverse)
map_df(my.stuff, ~ map_df(.x, ~
replace(.x, is.null(.x), NA)), .id = "my.var")
# A tibble: 4 x 5
# my.var my.col1 my.col2 my.col3 my.col4
# <chr> <dbl> <dbl> <dbl> <dbl>
#1 AA 1 4 NA NA
#2 BB NA NA NA NA
#3 CC 13 8 2 10
#4 DD NA NA -5 7
``` |
161,836 | I'm using Oracle 11g database in which I have more than 12 schema's consisting of many tables. I've created sequences for primary keys to these tables. I've also created synonyms to refer my application from the main schema.
My issue is,
while i try to export(using expdp) the schema's from DB in 1 server and import(impdp) the dump file to db installed in another server, sequence values only for some tables are getting changed. Even if i try to remap the table space or schemas, the value of sequence shows a lesser value than rows in their respective tables. Due to which when i access the application it throws an error while saving the data.
I am confused and don't getting an idea to solve this. Please advise.
Is their any method to solve this issue?
Thanks in advance. | 2017/01/21 | [
"https://dba.stackexchange.com/questions/161836",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/104331/"
] | If you run export command against live database without parameters like `flashback_scn` or `flashback_time` which ensures consistency during the export, then this can be an expected behavior because these objects are exported in different time and one can become inconsistent with another.
For example, if the sequence object is exported before the table and the application has inserted new records using the sequence and exported later then table and sequence can be out of sync.
Stopping application before starting the export process or using `expdp`parameters like `flashback_time`(this may not export all the transactions made after the time specified in this parameter unless you stop the application) can prevent this situation. Or you can adjust the sequence value after the import by recreating it. | You can drop and create SEQ again:
Example:
DB1: DB export
DB2: DB import
1. select list drop SEQ from DB2, after that, drop SEQ with list drop in DB2
```
SELECT
'DROP ' || OBJECT_TYPE || ' ' || OWNER || '.' || OBJECT_NAME || ';' "DROP SEQUENCE"
FROM DBA_OBJECTS
where owner in ('USER_1')
and object_type = 'SEQUENCE'
order by owner, object_name;
```
2. select list create SEQ from DB1, create SEQ with list create in DB2
```
select trim(DBMS_METADATA.GET_DDL('SEQUENCE',a.OBJECT_NAME, a.OWNER)) "SEQUENCE_DDL"
from dba_objects a
where a.OBJECT_TYPE ='SEQUENCE'
and a.OWNER in ('USER_1')
order by a.OWNER, a.OBJECT_NAME;
``` |
43,053,550 | I want to change the default login validation error message like:
```
Username & Password doesn't match
```
instead of
```
these credentials do not match our records
```
How to do this ? | 2017/03/27 | [
"https://Stackoverflow.com/questions/43053550",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/7394739/"
] | You can change this message to another one in this file:
```
resources/lang/en/auth.php
```
This is the line:
```
'failed' => 'These credentials do not match our records.',
``` | do one thing make new file message.php in lang folder then enter the error message in that and access in the controller and where you want to use like this
in Authonticateduser.php
```
protected function sendLoginResponse(Request $request) {
$request->session()->regenerate();
$this->clearLoginAttempts($request);
return $this->authenticated($request, $this->guard()->user())
? : redirect()->intended($this->redirectPath())->with('status', Lang::get('messege.login_success'));
}
```
and you get the perfect mesege you want instead of system mesege and without any change in default message. |
43,053,550 | I want to change the default login validation error message like:
```
Username & Password doesn't match
```
instead of
```
these credentials do not match our records
```
How to do this ? | 2017/03/27 | [
"https://Stackoverflow.com/questions/43053550",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/7394739/"
] | You can change this message to another one in this file:
```
resources/lang/en/auth.php
```
This is the line:
```
'failed' => 'These credentials do not match our records.',
``` | In `app/Http/controllers/Auth/LoginController` add below code:
```
protected function sendFailedLoginResponse(Request $request)
{
throw ValidationException::withMessages([
'username or password is incorrect!!!'
]);
}
```
In the `sendFailedLoginResponse` function you can redirect user to custom page or show error alert. |
43,053,550 | I want to change the default login validation error message like:
```
Username & Password doesn't match
```
instead of
```
these credentials do not match our records
```
How to do this ? | 2017/03/27 | [
"https://Stackoverflow.com/questions/43053550",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/7394739/"
] | In `app/Http/controllers/Auth/LoginController` add below code:
```
protected function sendFailedLoginResponse(Request $request)
{
throw ValidationException::withMessages([
'username or password is incorrect!!!'
]);
}
```
In the `sendFailedLoginResponse` function you can redirect user to custom page or show error alert. | do one thing make new file message.php in lang folder then enter the error message in that and access in the controller and where you want to use like this
in Authonticateduser.php
```
protected function sendLoginResponse(Request $request) {
$request->session()->regenerate();
$this->clearLoginAttempts($request);
return $this->authenticated($request, $this->guard()->user())
? : redirect()->intended($this->redirectPath())->with('status', Lang::get('messege.login_success'));
}
```
and you get the perfect mesege you want instead of system mesege and without any change in default message. |
4,378,067 | I need to find the GUID for an existing USB device attached to my Windows XP system. How can this be done using WMI or the registry? Or, is there another avenue that I should explore? Thanks.
**Additional Information:**
I need to find the GUID for a specific known device; it is not expected to change. If I need to write a little program, use some tool, or look somewhere in the Windows system to find this information, it's all the same to me. | 2010/12/07 | [
"https://Stackoverflow.com/questions/4378067",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/214296/"
] | For a specific known device, the easiest way I've found is to open the .inf file for that device's driver (if you have the driver); it should be clearly indicated there.
You can probably also poke around under HKEY\_LOCAL\_MACHINE\SYSTEM\CurrentControlSet\Enum\USB. | [DevViewer from Symantec](http://service1.symantec.com/SUPPORT/ent-security.nsf/ppfdocs/2007511906325898?Open&dtype=corp&src=&seg=&om=1&om_out=prod) also seems to do the trick. |
4,378,067 | I need to find the GUID for an existing USB device attached to my Windows XP system. How can this be done using WMI or the registry? Or, is there another avenue that I should explore? Thanks.
**Additional Information:**
I need to find the GUID for a specific known device; it is not expected to change. If I need to write a little program, use some tool, or look somewhere in the Windows system to find this information, it's all the same to me. | 2010/12/07 | [
"https://Stackoverflow.com/questions/4378067",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/214296/"
] | Control Panel > Device Manager > Right Click on Device > Properties > Details Tab > Change 'Property' to Driver Key > Guid will be displayed in 'value' section | [DevViewer from Symantec](http://service1.symantec.com/SUPPORT/ent-security.nsf/ppfdocs/2007511906325898?Open&dtype=corp&src=&seg=&om=1&om_out=prod) also seems to do the trick. |
12,104,391 | I am trying to instantiate the [StdRandom](http://algs4.cs.princeton.edu/stdlib/StdRandom.java.html) class (see below) in my own Java program so that I can generate random integers by calling it's *uniform* method. However, I kept getting this error during compilation:
>
> MyProgram.java:43: StdRandom() has private access in StdRandom
>
> StdRandom random = new StdRandom();
>
> 1 error
>
>
>
I noticed this line in the code which is preventing me from instantiating the StdRandom class:
```
// singleton pattern - can't instantiate
private StdRandom() { }
```
My questions are: how am I supposed to instantiate this class and use the methods in this class in my own programs? Why was the above singleton pattern included in this code? Should I just comment the pattern out and use it? Or is there another way to access this class's methods in my Java programs?
```
/*************************************************************************
* Compilation: javac StdRandom.java
* Execution: java StdRandom
*
* A library of static methods to generate pseudo-random numbers from
* different distributions (bernoulli, uniform, gaussian, discrete,
* and exponential). Also includes a method for shuffling an array.
*
*
* % java StdRandom 5
* seed = 1316600602069
* 59 16.81826 true 8.83954 0
* 32 91.32098 true 9.11026 0
* 35 10.11874 true 8.95396 3
* 92 32.88401 true 8.87089 0
* 72 92.55791 true 9.46241 0
*
* % java StdRandom 5
* seed = 1316600616575
* 96 60.17070 true 8.72821 0
* 79 32.01607 true 8.58159 0
* 81 59.49065 true 9.10423 1
* 96 51.65818 true 9.02102 0
* 99 17.55771 true 8.99762 0
*
* % java StdRandom 5 1316600616575
* seed = 1316600616575
* 96 60.17070 true 8.72821 0
* 79 32.01607 true 8.58159 0
* 81 59.49065 true 9.10423 1
* 96 51.65818 true 9.02102 0
* 99 17.55771 true 8.99762 0
*
*
* Remark
* ------
* - Relies on randomness of nextDouble() method in java.util.Random
* to generate pseudorandom numbers in [0, 1).
*
* - This library allows you to set and get the pseudorandom number seed.
*
* - See http://www.honeylocust.com/RngPack/ for an industrial
* strength random number generator in Java.
*
*************************************************************************/
import java.util.Random;
/**
* <i>Standard random</i>. This class provides methods for generating
* random number from various distributions.
* <p>
* For additional documentation, see <a href="http://introcs.cs.princeton.edu/22library">Section 2.2</a> of
* <i>Introduction to Programming in Java: An Interdisciplinary Approach</i> by Robert Sedgewick and Kevin Wayne.
*/
public final class StdRandom {
private static Random random; // pseudo-random number generator
private static long seed; // pseudo-random number generator seed
// static initializer
static {
// this is how the seed was set in Java 1.4
seed = System.currentTimeMillis();
random = new Random(seed);
}
// singleton pattern - can't instantiate
private StdRandom() { }
/**
* Set the seed of the psedurandom number generator.
*/
public static void setSeed(long s) {
seed = s;
random = new Random(seed);
}
/**
* Get the seed of the psedurandom number generator.
*/
public static long getSeed() {
return seed;
}
/**
* Return real number uniformly in [0, 1).
*/
public static double uniform() {
return random.nextDouble();
}
/**
* Return an integer uniformly between 0 and N-1.
*/
public static int uniform(int N) {
return random.nextInt(N);
}
///////////////////////////////////////////////////////////////////////////
// STATIC METHODS BELOW RELY ON JAVA.UTIL.RANDOM ONLY INDIRECTLY VIA
// THE STATIC METHODS ABOVE.
///////////////////////////////////////////////////////////////////////////
/**
* Return real number uniformly in [0, 1).
*/
public static double random() {
return uniform();
}
/**
* Return int uniformly in [a, b).
*/
public static int uniform(int a, int b) {
return a + uniform(b - a);
}
/**
* Return real number uniformly in [a, b).
*/
public static double uniform(double a, double b) {
return a + uniform() * (b-a);
}
/**
* Return a boolean, which is true with probability p, and false otherwise.
*/
public static boolean bernoulli(double p) {
return uniform() < p;
}
/**
* Return a boolean, which is true with probability .5, and false otherwise.
*/
public static boolean bernoulli() {
return bernoulli(0.5);
}
/**
* Return a real number with a standard Gaussian distribution.
*/
public static double gaussian() {
// use the polar form of the Box-Muller transform
double r, x, y;
do {
x = uniform(-1.0, 1.0);
y = uniform(-1.0, 1.0);
r = x*x + y*y;
} while (r >= 1 || r == 0);
return x * Math.sqrt(-2 * Math.log(r) / r);
// Remark: y * Math.sqrt(-2 * Math.log(r) / r)
// is an independent random gaussian
}
/**
* Return a real number from a gaussian distribution with given mean and stddev
*/
public static double gaussian(double mean, double stddev) {
return mean + stddev * gaussian();
}
/**
* Return an integer with a geometric distribution with mean 1/p.
*/
public static int geometric(double p) {
// using algorithm given by Knuth
return (int) Math.ceil(Math.log(uniform()) / Math.log(1.0 - p));
}
/**
* Return an integer with a Poisson distribution with mean lambda.
*/
public static int poisson(double lambda) {
// using algorithm given by Knuth
// see http://en.wikipedia.org/wiki/Poisson_distribution
int k = 0;
double p = 1.0;
double L = Math.exp(-lambda);
do {
k++;
p *= uniform();
} while (p >= L);
return k-1;
}
/**
* Return a real number with a Pareto distribution with parameter alpha.
*/
public static double pareto(double alpha) {
return Math.pow(1 - uniform(), -1.0/alpha) - 1.0;
}
/**
* Return a real number with a Cauchy distribution.
*/
public static double cauchy() {
return Math.tan(Math.PI * (uniform() - 0.5));
}
/**
* Return a number from a discrete distribution: i with probability a[i].
* Precondition: array entries are nonnegative and their sum equals 1.
*/
public static int discrete(double[] a) {
double EPSILON = 1E-14;
double sum = 0.0;
for (int i = 0; i < a.length; i++) {
if (a[i] < 0.0) throw new IllegalArgumentException("array entry " + i + " is negative: " + a[i]);
sum = sum + a[i];
}
if (sum > 1.0 + EPSILON || sum < 1.0 - EPSILON)
throw new IllegalArgumentException("sum of array entries not equal to one: " + sum);
double r = uniform();
sum = 0.0;
for (int i = 0; i < a.length; i++) {
sum = sum + a[i];
if (sum >= r) return i;
}
return -1;
}
/**
* Return a real number from an exponential distribution with rate lambda.
*/
public static double exp(double lambda) {
return -Math.log(1 - uniform()) / lambda;
}
/**
* Rearrange the elements of an array in random order.
*/
public static void shuffle(Object[] a) {
int N = a.length;
for (int i = 0; i < N; i++) {
int r = i + uniform(N-i); // between i and N-1
Object temp = a[i];
a[i] = a[r];
a[r] = temp;
}
}
/**
* Rearrange the elements of a double array in random order.
*/
public static void shuffle(double[] a) {
int N = a.length;
for (int i = 0; i < N; i++) {
int r = i + uniform(N-i); // between i and N-1
double temp = a[i];
a[i] = a[r];
a[r] = temp;
}
}
/**
* Rearrange the elements of an int array in random order.
*/
public static void shuffle(int[] a) {
int N = a.length;
for (int i = 0; i < N; i++) {
int r = i + uniform(N-i); // between i and N-1
int temp = a[i];
a[i] = a[r];
a[r] = temp;
}
}
/**
* Rearrange the elements of the subarray a[lo..hi] in random order.
*/
public static void shuffle(Object[] a, int lo, int hi) {
if (lo < 0 || lo > hi || hi >= a.length)
throw new RuntimeException("Illegal subarray range");
for (int i = lo; i <= hi; i++) {
int r = i + uniform(hi-i+1); // between i and hi
Object temp = a[i];
a[i] = a[r];
a[r] = temp;
}
}
/**
* Rearrange the elements of the subarray a[lo..hi] in random order.
*/
public static void shuffle(double[] a, int lo, int hi) {
if (lo < 0 || lo > hi || hi >= a.length)
throw new RuntimeException("Illegal subarray range");
for (int i = lo; i <= hi; i++) {
int r = i + uniform(hi-i+1); // between i and hi
double temp = a[i];
a[i] = a[r];
a[r] = temp;
}
}
/**
* Rearrange the elements of the subarray a[lo..hi] in random order.
*/
public static void shuffle(int[] a, int lo, int hi) {
if (lo < 0 || lo > hi || hi >= a.length)
throw new RuntimeException("Illegal subarray range");
for (int i = lo; i <= hi; i++) {
int r = i + uniform(hi-i+1); // between i and hi
int temp = a[i];
a[i] = a[r];
a[r] = temp;
}
}
/**
* Uniformly sample (without replacement) M of the N items from the array a[].
* To make it work with an Object[] argument and return an array of the
* underlying argument type requires some Java minutiae, e.g., using static
* generics and Arrays.copyOf().
*/
public static String[] sample(String[] a, int M) {
int N = a.length;
if (M < 0 || M > N)
throw new RuntimeException("Illegal number of samples");
String[] b = new String[M];
for (int i = 0; i < N; i++) {
int r = uniform(i+1); // between 0 and i
if (r < M) {
if (i < M) b[i] = b[r];
b[r] = a[i];
}
}
return b;
}
/**
* Unit test.
*/
public static void main(String[] args) {
int N = Integer.parseInt(args[0]);
if (args.length == 2) StdRandom.setSeed(Long.parseLong(args[1]));
double[] t = { .5, .3, .1, .1 };
StdOut.println("seed = " + StdRandom.getSeed());
for (int i = 0; i < N; i++) {
StdOut.printf("%2d " , uniform(100));
StdOut.printf("%8.5f ", uniform(10.0, 99.0));
StdOut.printf("%5b " , bernoulli(.5));
StdOut.printf("%7.5f ", gaussian(9.0, .2));
StdOut.printf("%2d " , discrete(t));
StdOut.println();
}
String[] a = "A B C D E F G".split(" ");
for (String s : a)
StdOut.print(s + " ");
StdOut.println();
String[] b = StdRandom.sample(a, 3);
for (String s : b)
StdOut.print(s + " ");
StdOut.println();
}
}
``` | 2012/08/24 | [
"https://Stackoverflow.com/questions/12104391",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/225998/"
] | All methods are static, you don't need to create an instance of that class to use it. To use e.g. the `random()` method, use `StdRandom.random()` | You don't instantiate it, you call the methods statically:
```
StdRandom.setSeed(42L);
double n = StdRandom.uniform(66);
```
etc. |
12,104,391 | I am trying to instantiate the [StdRandom](http://algs4.cs.princeton.edu/stdlib/StdRandom.java.html) class (see below) in my own Java program so that I can generate random integers by calling it's *uniform* method. However, I kept getting this error during compilation:
>
> MyProgram.java:43: StdRandom() has private access in StdRandom
>
> StdRandom random = new StdRandom();
>
> 1 error
>
>
>
I noticed this line in the code which is preventing me from instantiating the StdRandom class:
```
// singleton pattern - can't instantiate
private StdRandom() { }
```
My questions are: how am I supposed to instantiate this class and use the methods in this class in my own programs? Why was the above singleton pattern included in this code? Should I just comment the pattern out and use it? Or is there another way to access this class's methods in my Java programs?
```
/*************************************************************************
* Compilation: javac StdRandom.java
* Execution: java StdRandom
*
* A library of static methods to generate pseudo-random numbers from
* different distributions (bernoulli, uniform, gaussian, discrete,
* and exponential). Also includes a method for shuffling an array.
*
*
* % java StdRandom 5
* seed = 1316600602069
* 59 16.81826 true 8.83954 0
* 32 91.32098 true 9.11026 0
* 35 10.11874 true 8.95396 3
* 92 32.88401 true 8.87089 0
* 72 92.55791 true 9.46241 0
*
* % java StdRandom 5
* seed = 1316600616575
* 96 60.17070 true 8.72821 0
* 79 32.01607 true 8.58159 0
* 81 59.49065 true 9.10423 1
* 96 51.65818 true 9.02102 0
* 99 17.55771 true 8.99762 0
*
* % java StdRandom 5 1316600616575
* seed = 1316600616575
* 96 60.17070 true 8.72821 0
* 79 32.01607 true 8.58159 0
* 81 59.49065 true 9.10423 1
* 96 51.65818 true 9.02102 0
* 99 17.55771 true 8.99762 0
*
*
* Remark
* ------
* - Relies on randomness of nextDouble() method in java.util.Random
* to generate pseudorandom numbers in [0, 1).
*
* - This library allows you to set and get the pseudorandom number seed.
*
* - See http://www.honeylocust.com/RngPack/ for an industrial
* strength random number generator in Java.
*
*************************************************************************/
import java.util.Random;
/**
* <i>Standard random</i>. This class provides methods for generating
* random number from various distributions.
* <p>
* For additional documentation, see <a href="http://introcs.cs.princeton.edu/22library">Section 2.2</a> of
* <i>Introduction to Programming in Java: An Interdisciplinary Approach</i> by Robert Sedgewick and Kevin Wayne.
*/
public final class StdRandom {
private static Random random; // pseudo-random number generator
private static long seed; // pseudo-random number generator seed
// static initializer
static {
// this is how the seed was set in Java 1.4
seed = System.currentTimeMillis();
random = new Random(seed);
}
// singleton pattern - can't instantiate
private StdRandom() { }
/**
* Set the seed of the psedurandom number generator.
*/
public static void setSeed(long s) {
seed = s;
random = new Random(seed);
}
/**
* Get the seed of the psedurandom number generator.
*/
public static long getSeed() {
return seed;
}
/**
* Return real number uniformly in [0, 1).
*/
public static double uniform() {
return random.nextDouble();
}
/**
* Return an integer uniformly between 0 and N-1.
*/
public static int uniform(int N) {
return random.nextInt(N);
}
///////////////////////////////////////////////////////////////////////////
// STATIC METHODS BELOW RELY ON JAVA.UTIL.RANDOM ONLY INDIRECTLY VIA
// THE STATIC METHODS ABOVE.
///////////////////////////////////////////////////////////////////////////
/**
* Return real number uniformly in [0, 1).
*/
public static double random() {
return uniform();
}
/**
* Return int uniformly in [a, b).
*/
public static int uniform(int a, int b) {
return a + uniform(b - a);
}
/**
* Return real number uniformly in [a, b).
*/
public static double uniform(double a, double b) {
return a + uniform() * (b-a);
}
/**
* Return a boolean, which is true with probability p, and false otherwise.
*/
public static boolean bernoulli(double p) {
return uniform() < p;
}
/**
* Return a boolean, which is true with probability .5, and false otherwise.
*/
public static boolean bernoulli() {
return bernoulli(0.5);
}
/**
* Return a real number with a standard Gaussian distribution.
*/
public static double gaussian() {
// use the polar form of the Box-Muller transform
double r, x, y;
do {
x = uniform(-1.0, 1.0);
y = uniform(-1.0, 1.0);
r = x*x + y*y;
} while (r >= 1 || r == 0);
return x * Math.sqrt(-2 * Math.log(r) / r);
// Remark: y * Math.sqrt(-2 * Math.log(r) / r)
// is an independent random gaussian
}
/**
* Return a real number from a gaussian distribution with given mean and stddev
*/
public static double gaussian(double mean, double stddev) {
return mean + stddev * gaussian();
}
/**
* Return an integer with a geometric distribution with mean 1/p.
*/
public static int geometric(double p) {
// using algorithm given by Knuth
return (int) Math.ceil(Math.log(uniform()) / Math.log(1.0 - p));
}
/**
* Return an integer with a Poisson distribution with mean lambda.
*/
public static int poisson(double lambda) {
// using algorithm given by Knuth
// see http://en.wikipedia.org/wiki/Poisson_distribution
int k = 0;
double p = 1.0;
double L = Math.exp(-lambda);
do {
k++;
p *= uniform();
} while (p >= L);
return k-1;
}
/**
* Return a real number with a Pareto distribution with parameter alpha.
*/
public static double pareto(double alpha) {
return Math.pow(1 - uniform(), -1.0/alpha) - 1.0;
}
/**
* Return a real number with a Cauchy distribution.
*/
public static double cauchy() {
return Math.tan(Math.PI * (uniform() - 0.5));
}
/**
* Return a number from a discrete distribution: i with probability a[i].
* Precondition: array entries are nonnegative and their sum equals 1.
*/
public static int discrete(double[] a) {
double EPSILON = 1E-14;
double sum = 0.0;
for (int i = 0; i < a.length; i++) {
if (a[i] < 0.0) throw new IllegalArgumentException("array entry " + i + " is negative: " + a[i]);
sum = sum + a[i];
}
if (sum > 1.0 + EPSILON || sum < 1.0 - EPSILON)
throw new IllegalArgumentException("sum of array entries not equal to one: " + sum);
double r = uniform();
sum = 0.0;
for (int i = 0; i < a.length; i++) {
sum = sum + a[i];
if (sum >= r) return i;
}
return -1;
}
/**
* Return a real number from an exponential distribution with rate lambda.
*/
public static double exp(double lambda) {
return -Math.log(1 - uniform()) / lambda;
}
/**
* Rearrange the elements of an array in random order.
*/
public static void shuffle(Object[] a) {
int N = a.length;
for (int i = 0; i < N; i++) {
int r = i + uniform(N-i); // between i and N-1
Object temp = a[i];
a[i] = a[r];
a[r] = temp;
}
}
/**
* Rearrange the elements of a double array in random order.
*/
public static void shuffle(double[] a) {
int N = a.length;
for (int i = 0; i < N; i++) {
int r = i + uniform(N-i); // between i and N-1
double temp = a[i];
a[i] = a[r];
a[r] = temp;
}
}
/**
* Rearrange the elements of an int array in random order.
*/
public static void shuffle(int[] a) {
int N = a.length;
for (int i = 0; i < N; i++) {
int r = i + uniform(N-i); // between i and N-1
int temp = a[i];
a[i] = a[r];
a[r] = temp;
}
}
/**
* Rearrange the elements of the subarray a[lo..hi] in random order.
*/
public static void shuffle(Object[] a, int lo, int hi) {
if (lo < 0 || lo > hi || hi >= a.length)
throw new RuntimeException("Illegal subarray range");
for (int i = lo; i <= hi; i++) {
int r = i + uniform(hi-i+1); // between i and hi
Object temp = a[i];
a[i] = a[r];
a[r] = temp;
}
}
/**
* Rearrange the elements of the subarray a[lo..hi] in random order.
*/
public static void shuffle(double[] a, int lo, int hi) {
if (lo < 0 || lo > hi || hi >= a.length)
throw new RuntimeException("Illegal subarray range");
for (int i = lo; i <= hi; i++) {
int r = i + uniform(hi-i+1); // between i and hi
double temp = a[i];
a[i] = a[r];
a[r] = temp;
}
}
/**
* Rearrange the elements of the subarray a[lo..hi] in random order.
*/
public static void shuffle(int[] a, int lo, int hi) {
if (lo < 0 || lo > hi || hi >= a.length)
throw new RuntimeException("Illegal subarray range");
for (int i = lo; i <= hi; i++) {
int r = i + uniform(hi-i+1); // between i and hi
int temp = a[i];
a[i] = a[r];
a[r] = temp;
}
}
/**
* Uniformly sample (without replacement) M of the N items from the array a[].
* To make it work with an Object[] argument and return an array of the
* underlying argument type requires some Java minutiae, e.g., using static
* generics and Arrays.copyOf().
*/
public static String[] sample(String[] a, int M) {
int N = a.length;
if (M < 0 || M > N)
throw new RuntimeException("Illegal number of samples");
String[] b = new String[M];
for (int i = 0; i < N; i++) {
int r = uniform(i+1); // between 0 and i
if (r < M) {
if (i < M) b[i] = b[r];
b[r] = a[i];
}
}
return b;
}
/**
* Unit test.
*/
public static void main(String[] args) {
int N = Integer.parseInt(args[0]);
if (args.length == 2) StdRandom.setSeed(Long.parseLong(args[1]));
double[] t = { .5, .3, .1, .1 };
StdOut.println("seed = " + StdRandom.getSeed());
for (int i = 0; i < N; i++) {
StdOut.printf("%2d " , uniform(100));
StdOut.printf("%8.5f ", uniform(10.0, 99.0));
StdOut.printf("%5b " , bernoulli(.5));
StdOut.printf("%7.5f ", gaussian(9.0, .2));
StdOut.printf("%2d " , discrete(t));
StdOut.println();
}
String[] a = "A B C D E F G".split(" ");
for (String s : a)
StdOut.print(s + " ");
StdOut.println();
String[] b = StdRandom.sample(a, 3);
for (String s : b)
StdOut.print(s + " ");
StdOut.println();
}
}
``` | 2012/08/24 | [
"https://Stackoverflow.com/questions/12104391",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/225998/"
] | All methods are static, you don't need to create an instance of that class to use it. To use e.g. the `random()` method, use `StdRandom.random()` | All the methods in this class are static, you don't need to and can't instantiate as it has private constructor, you can use methods directly for eg `StdRandom.unifrom(...)` |
12,104,391 | I am trying to instantiate the [StdRandom](http://algs4.cs.princeton.edu/stdlib/StdRandom.java.html) class (see below) in my own Java program so that I can generate random integers by calling it's *uniform* method. However, I kept getting this error during compilation:
>
> MyProgram.java:43: StdRandom() has private access in StdRandom
>
> StdRandom random = new StdRandom();
>
> 1 error
>
>
>
I noticed this line in the code which is preventing me from instantiating the StdRandom class:
```
// singleton pattern - can't instantiate
private StdRandom() { }
```
My questions are: how am I supposed to instantiate this class and use the methods in this class in my own programs? Why was the above singleton pattern included in this code? Should I just comment the pattern out and use it? Or is there another way to access this class's methods in my Java programs?
```
/*************************************************************************
* Compilation: javac StdRandom.java
* Execution: java StdRandom
*
* A library of static methods to generate pseudo-random numbers from
* different distributions (bernoulli, uniform, gaussian, discrete,
* and exponential). Also includes a method for shuffling an array.
*
*
* % java StdRandom 5
* seed = 1316600602069
* 59 16.81826 true 8.83954 0
* 32 91.32098 true 9.11026 0
* 35 10.11874 true 8.95396 3
* 92 32.88401 true 8.87089 0
* 72 92.55791 true 9.46241 0
*
* % java StdRandom 5
* seed = 1316600616575
* 96 60.17070 true 8.72821 0
* 79 32.01607 true 8.58159 0
* 81 59.49065 true 9.10423 1
* 96 51.65818 true 9.02102 0
* 99 17.55771 true 8.99762 0
*
* % java StdRandom 5 1316600616575
* seed = 1316600616575
* 96 60.17070 true 8.72821 0
* 79 32.01607 true 8.58159 0
* 81 59.49065 true 9.10423 1
* 96 51.65818 true 9.02102 0
* 99 17.55771 true 8.99762 0
*
*
* Remark
* ------
* - Relies on randomness of nextDouble() method in java.util.Random
* to generate pseudorandom numbers in [0, 1).
*
* - This library allows you to set and get the pseudorandom number seed.
*
* - See http://www.honeylocust.com/RngPack/ for an industrial
* strength random number generator in Java.
*
*************************************************************************/
import java.util.Random;
/**
* <i>Standard random</i>. This class provides methods for generating
* random number from various distributions.
* <p>
* For additional documentation, see <a href="http://introcs.cs.princeton.edu/22library">Section 2.2</a> of
* <i>Introduction to Programming in Java: An Interdisciplinary Approach</i> by Robert Sedgewick and Kevin Wayne.
*/
public final class StdRandom {
private static Random random; // pseudo-random number generator
private static long seed; // pseudo-random number generator seed
// static initializer
static {
// this is how the seed was set in Java 1.4
seed = System.currentTimeMillis();
random = new Random(seed);
}
// singleton pattern - can't instantiate
private StdRandom() { }
/**
* Set the seed of the psedurandom number generator.
*/
public static void setSeed(long s) {
seed = s;
random = new Random(seed);
}
/**
* Get the seed of the psedurandom number generator.
*/
public static long getSeed() {
return seed;
}
/**
* Return real number uniformly in [0, 1).
*/
public static double uniform() {
return random.nextDouble();
}
/**
* Return an integer uniformly between 0 and N-1.
*/
public static int uniform(int N) {
return random.nextInt(N);
}
///////////////////////////////////////////////////////////////////////////
// STATIC METHODS BELOW RELY ON JAVA.UTIL.RANDOM ONLY INDIRECTLY VIA
// THE STATIC METHODS ABOVE.
///////////////////////////////////////////////////////////////////////////
/**
* Return real number uniformly in [0, 1).
*/
public static double random() {
return uniform();
}
/**
* Return int uniformly in [a, b).
*/
public static int uniform(int a, int b) {
return a + uniform(b - a);
}
/**
* Return real number uniformly in [a, b).
*/
public static double uniform(double a, double b) {
return a + uniform() * (b-a);
}
/**
* Return a boolean, which is true with probability p, and false otherwise.
*/
public static boolean bernoulli(double p) {
return uniform() < p;
}
/**
* Return a boolean, which is true with probability .5, and false otherwise.
*/
public static boolean bernoulli() {
return bernoulli(0.5);
}
/**
* Return a real number with a standard Gaussian distribution.
*/
public static double gaussian() {
// use the polar form of the Box-Muller transform
double r, x, y;
do {
x = uniform(-1.0, 1.0);
y = uniform(-1.0, 1.0);
r = x*x + y*y;
} while (r >= 1 || r == 0);
return x * Math.sqrt(-2 * Math.log(r) / r);
// Remark: y * Math.sqrt(-2 * Math.log(r) / r)
// is an independent random gaussian
}
/**
* Return a real number from a gaussian distribution with given mean and stddev
*/
public static double gaussian(double mean, double stddev) {
return mean + stddev * gaussian();
}
/**
* Return an integer with a geometric distribution with mean 1/p.
*/
public static int geometric(double p) {
// using algorithm given by Knuth
return (int) Math.ceil(Math.log(uniform()) / Math.log(1.0 - p));
}
/**
* Return an integer with a Poisson distribution with mean lambda.
*/
public static int poisson(double lambda) {
// using algorithm given by Knuth
// see http://en.wikipedia.org/wiki/Poisson_distribution
int k = 0;
double p = 1.0;
double L = Math.exp(-lambda);
do {
k++;
p *= uniform();
} while (p >= L);
return k-1;
}
/**
* Return a real number with a Pareto distribution with parameter alpha.
*/
public static double pareto(double alpha) {
return Math.pow(1 - uniform(), -1.0/alpha) - 1.0;
}
/**
* Return a real number with a Cauchy distribution.
*/
public static double cauchy() {
return Math.tan(Math.PI * (uniform() - 0.5));
}
/**
* Return a number from a discrete distribution: i with probability a[i].
* Precondition: array entries are nonnegative and their sum equals 1.
*/
public static int discrete(double[] a) {
double EPSILON = 1E-14;
double sum = 0.0;
for (int i = 0; i < a.length; i++) {
if (a[i] < 0.0) throw new IllegalArgumentException("array entry " + i + " is negative: " + a[i]);
sum = sum + a[i];
}
if (sum > 1.0 + EPSILON || sum < 1.0 - EPSILON)
throw new IllegalArgumentException("sum of array entries not equal to one: " + sum);
double r = uniform();
sum = 0.0;
for (int i = 0; i < a.length; i++) {
sum = sum + a[i];
if (sum >= r) return i;
}
return -1;
}
/**
* Return a real number from an exponential distribution with rate lambda.
*/
public static double exp(double lambda) {
return -Math.log(1 - uniform()) / lambda;
}
/**
* Rearrange the elements of an array in random order.
*/
public static void shuffle(Object[] a) {
int N = a.length;
for (int i = 0; i < N; i++) {
int r = i + uniform(N-i); // between i and N-1
Object temp = a[i];
a[i] = a[r];
a[r] = temp;
}
}
/**
* Rearrange the elements of a double array in random order.
*/
public static void shuffle(double[] a) {
int N = a.length;
for (int i = 0; i < N; i++) {
int r = i + uniform(N-i); // between i and N-1
double temp = a[i];
a[i] = a[r];
a[r] = temp;
}
}
/**
* Rearrange the elements of an int array in random order.
*/
public static void shuffle(int[] a) {
int N = a.length;
for (int i = 0; i < N; i++) {
int r = i + uniform(N-i); // between i and N-1
int temp = a[i];
a[i] = a[r];
a[r] = temp;
}
}
/**
* Rearrange the elements of the subarray a[lo..hi] in random order.
*/
public static void shuffle(Object[] a, int lo, int hi) {
if (lo < 0 || lo > hi || hi >= a.length)
throw new RuntimeException("Illegal subarray range");
for (int i = lo; i <= hi; i++) {
int r = i + uniform(hi-i+1); // between i and hi
Object temp = a[i];
a[i] = a[r];
a[r] = temp;
}
}
/**
* Rearrange the elements of the subarray a[lo..hi] in random order.
*/
public static void shuffle(double[] a, int lo, int hi) {
if (lo < 0 || lo > hi || hi >= a.length)
throw new RuntimeException("Illegal subarray range");
for (int i = lo; i <= hi; i++) {
int r = i + uniform(hi-i+1); // between i and hi
double temp = a[i];
a[i] = a[r];
a[r] = temp;
}
}
/**
* Rearrange the elements of the subarray a[lo..hi] in random order.
*/
public static void shuffle(int[] a, int lo, int hi) {
if (lo < 0 || lo > hi || hi >= a.length)
throw new RuntimeException("Illegal subarray range");
for (int i = lo; i <= hi; i++) {
int r = i + uniform(hi-i+1); // between i and hi
int temp = a[i];
a[i] = a[r];
a[r] = temp;
}
}
/**
* Uniformly sample (without replacement) M of the N items from the array a[].
* To make it work with an Object[] argument and return an array of the
* underlying argument type requires some Java minutiae, e.g., using static
* generics and Arrays.copyOf().
*/
public static String[] sample(String[] a, int M) {
int N = a.length;
if (M < 0 || M > N)
throw new RuntimeException("Illegal number of samples");
String[] b = new String[M];
for (int i = 0; i < N; i++) {
int r = uniform(i+1); // between 0 and i
if (r < M) {
if (i < M) b[i] = b[r];
b[r] = a[i];
}
}
return b;
}
/**
* Unit test.
*/
public static void main(String[] args) {
int N = Integer.parseInt(args[0]);
if (args.length == 2) StdRandom.setSeed(Long.parseLong(args[1]));
double[] t = { .5, .3, .1, .1 };
StdOut.println("seed = " + StdRandom.getSeed());
for (int i = 0; i < N; i++) {
StdOut.printf("%2d " , uniform(100));
StdOut.printf("%8.5f ", uniform(10.0, 99.0));
StdOut.printf("%5b " , bernoulli(.5));
StdOut.printf("%7.5f ", gaussian(9.0, .2));
StdOut.printf("%2d " , discrete(t));
StdOut.println();
}
String[] a = "A B C D E F G".split(" ");
for (String s : a)
StdOut.print(s + " ");
StdOut.println();
String[] b = StdRandom.sample(a, 3);
for (String s : b)
StdOut.print(s + " ");
StdOut.println();
}
}
``` | 2012/08/24 | [
"https://Stackoverflow.com/questions/12104391",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/225998/"
] | All methods are static, you don't need to create an instance of that class to use it. To use e.g. the `random()` method, use `StdRandom.random()` | This is 'util' class with hidden constructor. Instead of create new instance call methods directly: `StdRandom.uniform(100)`, `StdRandom.random()`, etc.. |
12,104,391 | I am trying to instantiate the [StdRandom](http://algs4.cs.princeton.edu/stdlib/StdRandom.java.html) class (see below) in my own Java program so that I can generate random integers by calling it's *uniform* method. However, I kept getting this error during compilation:
>
> MyProgram.java:43: StdRandom() has private access in StdRandom
>
> StdRandom random = new StdRandom();
>
> 1 error
>
>
>
I noticed this line in the code which is preventing me from instantiating the StdRandom class:
```
// singleton pattern - can't instantiate
private StdRandom() { }
```
My questions are: how am I supposed to instantiate this class and use the methods in this class in my own programs? Why was the above singleton pattern included in this code? Should I just comment the pattern out and use it? Or is there another way to access this class's methods in my Java programs?
```
/*************************************************************************
* Compilation: javac StdRandom.java
* Execution: java StdRandom
*
* A library of static methods to generate pseudo-random numbers from
* different distributions (bernoulli, uniform, gaussian, discrete,
* and exponential). Also includes a method for shuffling an array.
*
*
* % java StdRandom 5
* seed = 1316600602069
* 59 16.81826 true 8.83954 0
* 32 91.32098 true 9.11026 0
* 35 10.11874 true 8.95396 3
* 92 32.88401 true 8.87089 0
* 72 92.55791 true 9.46241 0
*
* % java StdRandom 5
* seed = 1316600616575
* 96 60.17070 true 8.72821 0
* 79 32.01607 true 8.58159 0
* 81 59.49065 true 9.10423 1
* 96 51.65818 true 9.02102 0
* 99 17.55771 true 8.99762 0
*
* % java StdRandom 5 1316600616575
* seed = 1316600616575
* 96 60.17070 true 8.72821 0
* 79 32.01607 true 8.58159 0
* 81 59.49065 true 9.10423 1
* 96 51.65818 true 9.02102 0
* 99 17.55771 true 8.99762 0
*
*
* Remark
* ------
* - Relies on randomness of nextDouble() method in java.util.Random
* to generate pseudorandom numbers in [0, 1).
*
* - This library allows you to set and get the pseudorandom number seed.
*
* - See http://www.honeylocust.com/RngPack/ for an industrial
* strength random number generator in Java.
*
*************************************************************************/
import java.util.Random;
/**
* <i>Standard random</i>. This class provides methods for generating
* random number from various distributions.
* <p>
* For additional documentation, see <a href="http://introcs.cs.princeton.edu/22library">Section 2.2</a> of
* <i>Introduction to Programming in Java: An Interdisciplinary Approach</i> by Robert Sedgewick and Kevin Wayne.
*/
public final class StdRandom {
private static Random random; // pseudo-random number generator
private static long seed; // pseudo-random number generator seed
// static initializer
static {
// this is how the seed was set in Java 1.4
seed = System.currentTimeMillis();
random = new Random(seed);
}
// singleton pattern - can't instantiate
private StdRandom() { }
/**
* Set the seed of the psedurandom number generator.
*/
public static void setSeed(long s) {
seed = s;
random = new Random(seed);
}
/**
* Get the seed of the psedurandom number generator.
*/
public static long getSeed() {
return seed;
}
/**
* Return real number uniformly in [0, 1).
*/
public static double uniform() {
return random.nextDouble();
}
/**
* Return an integer uniformly between 0 and N-1.
*/
public static int uniform(int N) {
return random.nextInt(N);
}
///////////////////////////////////////////////////////////////////////////
// STATIC METHODS BELOW RELY ON JAVA.UTIL.RANDOM ONLY INDIRECTLY VIA
// THE STATIC METHODS ABOVE.
///////////////////////////////////////////////////////////////////////////
/**
* Return real number uniformly in [0, 1).
*/
public static double random() {
return uniform();
}
/**
* Return int uniformly in [a, b).
*/
public static int uniform(int a, int b) {
return a + uniform(b - a);
}
/**
* Return real number uniformly in [a, b).
*/
public static double uniform(double a, double b) {
return a + uniform() * (b-a);
}
/**
* Return a boolean, which is true with probability p, and false otherwise.
*/
public static boolean bernoulli(double p) {
return uniform() < p;
}
/**
* Return a boolean, which is true with probability .5, and false otherwise.
*/
public static boolean bernoulli() {
return bernoulli(0.5);
}
/**
* Return a real number with a standard Gaussian distribution.
*/
public static double gaussian() {
// use the polar form of the Box-Muller transform
double r, x, y;
do {
x = uniform(-1.0, 1.0);
y = uniform(-1.0, 1.0);
r = x*x + y*y;
} while (r >= 1 || r == 0);
return x * Math.sqrt(-2 * Math.log(r) / r);
// Remark: y * Math.sqrt(-2 * Math.log(r) / r)
// is an independent random gaussian
}
/**
* Return a real number from a gaussian distribution with given mean and stddev
*/
public static double gaussian(double mean, double stddev) {
return mean + stddev * gaussian();
}
/**
* Return an integer with a geometric distribution with mean 1/p.
*/
public static int geometric(double p) {
// using algorithm given by Knuth
return (int) Math.ceil(Math.log(uniform()) / Math.log(1.0 - p));
}
/**
* Return an integer with a Poisson distribution with mean lambda.
*/
public static int poisson(double lambda) {
// using algorithm given by Knuth
// see http://en.wikipedia.org/wiki/Poisson_distribution
int k = 0;
double p = 1.0;
double L = Math.exp(-lambda);
do {
k++;
p *= uniform();
} while (p >= L);
return k-1;
}
/**
* Return a real number with a Pareto distribution with parameter alpha.
*/
public static double pareto(double alpha) {
return Math.pow(1 - uniform(), -1.0/alpha) - 1.0;
}
/**
* Return a real number with a Cauchy distribution.
*/
public static double cauchy() {
return Math.tan(Math.PI * (uniform() - 0.5));
}
/**
* Return a number from a discrete distribution: i with probability a[i].
* Precondition: array entries are nonnegative and their sum equals 1.
*/
public static int discrete(double[] a) {
double EPSILON = 1E-14;
double sum = 0.0;
for (int i = 0; i < a.length; i++) {
if (a[i] < 0.0) throw new IllegalArgumentException("array entry " + i + " is negative: " + a[i]);
sum = sum + a[i];
}
if (sum > 1.0 + EPSILON || sum < 1.0 - EPSILON)
throw new IllegalArgumentException("sum of array entries not equal to one: " + sum);
double r = uniform();
sum = 0.0;
for (int i = 0; i < a.length; i++) {
sum = sum + a[i];
if (sum >= r) return i;
}
return -1;
}
/**
* Return a real number from an exponential distribution with rate lambda.
*/
public static double exp(double lambda) {
return -Math.log(1 - uniform()) / lambda;
}
/**
* Rearrange the elements of an array in random order.
*/
public static void shuffle(Object[] a) {
int N = a.length;
for (int i = 0; i < N; i++) {
int r = i + uniform(N-i); // between i and N-1
Object temp = a[i];
a[i] = a[r];
a[r] = temp;
}
}
/**
* Rearrange the elements of a double array in random order.
*/
public static void shuffle(double[] a) {
int N = a.length;
for (int i = 0; i < N; i++) {
int r = i + uniform(N-i); // between i and N-1
double temp = a[i];
a[i] = a[r];
a[r] = temp;
}
}
/**
* Rearrange the elements of an int array in random order.
*/
public static void shuffle(int[] a) {
int N = a.length;
for (int i = 0; i < N; i++) {
int r = i + uniform(N-i); // between i and N-1
int temp = a[i];
a[i] = a[r];
a[r] = temp;
}
}
/**
* Rearrange the elements of the subarray a[lo..hi] in random order.
*/
public static void shuffle(Object[] a, int lo, int hi) {
if (lo < 0 || lo > hi || hi >= a.length)
throw new RuntimeException("Illegal subarray range");
for (int i = lo; i <= hi; i++) {
int r = i + uniform(hi-i+1); // between i and hi
Object temp = a[i];
a[i] = a[r];
a[r] = temp;
}
}
/**
* Rearrange the elements of the subarray a[lo..hi] in random order.
*/
public static void shuffle(double[] a, int lo, int hi) {
if (lo < 0 || lo > hi || hi >= a.length)
throw new RuntimeException("Illegal subarray range");
for (int i = lo; i <= hi; i++) {
int r = i + uniform(hi-i+1); // between i and hi
double temp = a[i];
a[i] = a[r];
a[r] = temp;
}
}
/**
* Rearrange the elements of the subarray a[lo..hi] in random order.
*/
public static void shuffle(int[] a, int lo, int hi) {
if (lo < 0 || lo > hi || hi >= a.length)
throw new RuntimeException("Illegal subarray range");
for (int i = lo; i <= hi; i++) {
int r = i + uniform(hi-i+1); // between i and hi
int temp = a[i];
a[i] = a[r];
a[r] = temp;
}
}
/**
* Uniformly sample (without replacement) M of the N items from the array a[].
* To make it work with an Object[] argument and return an array of the
* underlying argument type requires some Java minutiae, e.g., using static
* generics and Arrays.copyOf().
*/
public static String[] sample(String[] a, int M) {
int N = a.length;
if (M < 0 || M > N)
throw new RuntimeException("Illegal number of samples");
String[] b = new String[M];
for (int i = 0; i < N; i++) {
int r = uniform(i+1); // between 0 and i
if (r < M) {
if (i < M) b[i] = b[r];
b[r] = a[i];
}
}
return b;
}
/**
* Unit test.
*/
public static void main(String[] args) {
int N = Integer.parseInt(args[0]);
if (args.length == 2) StdRandom.setSeed(Long.parseLong(args[1]));
double[] t = { .5, .3, .1, .1 };
StdOut.println("seed = " + StdRandom.getSeed());
for (int i = 0; i < N; i++) {
StdOut.printf("%2d " , uniform(100));
StdOut.printf("%8.5f ", uniform(10.0, 99.0));
StdOut.printf("%5b " , bernoulli(.5));
StdOut.printf("%7.5f ", gaussian(9.0, .2));
StdOut.printf("%2d " , discrete(t));
StdOut.println();
}
String[] a = "A B C D E F G".split(" ");
for (String s : a)
StdOut.print(s + " ");
StdOut.println();
String[] b = StdRandom.sample(a, 3);
for (String s : b)
StdOut.print(s + " ");
StdOut.println();
}
}
``` | 2012/08/24 | [
"https://Stackoverflow.com/questions/12104391",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/225998/"
] | You don't instantiate it, you call the methods statically:
```
StdRandom.setSeed(42L);
double n = StdRandom.uniform(66);
```
etc. | All the methods in this class are static, you don't need to and can't instantiate as it has private constructor, you can use methods directly for eg `StdRandom.unifrom(...)` |
12,104,391 | I am trying to instantiate the [StdRandom](http://algs4.cs.princeton.edu/stdlib/StdRandom.java.html) class (see below) in my own Java program so that I can generate random integers by calling it's *uniform* method. However, I kept getting this error during compilation:
>
> MyProgram.java:43: StdRandom() has private access in StdRandom
>
> StdRandom random = new StdRandom();
>
> 1 error
>
>
>
I noticed this line in the code which is preventing me from instantiating the StdRandom class:
```
// singleton pattern - can't instantiate
private StdRandom() { }
```
My questions are: how am I supposed to instantiate this class and use the methods in this class in my own programs? Why was the above singleton pattern included in this code? Should I just comment the pattern out and use it? Or is there another way to access this class's methods in my Java programs?
```
/*************************************************************************
* Compilation: javac StdRandom.java
* Execution: java StdRandom
*
* A library of static methods to generate pseudo-random numbers from
* different distributions (bernoulli, uniform, gaussian, discrete,
* and exponential). Also includes a method for shuffling an array.
*
*
* % java StdRandom 5
* seed = 1316600602069
* 59 16.81826 true 8.83954 0
* 32 91.32098 true 9.11026 0
* 35 10.11874 true 8.95396 3
* 92 32.88401 true 8.87089 0
* 72 92.55791 true 9.46241 0
*
* % java StdRandom 5
* seed = 1316600616575
* 96 60.17070 true 8.72821 0
* 79 32.01607 true 8.58159 0
* 81 59.49065 true 9.10423 1
* 96 51.65818 true 9.02102 0
* 99 17.55771 true 8.99762 0
*
* % java StdRandom 5 1316600616575
* seed = 1316600616575
* 96 60.17070 true 8.72821 0
* 79 32.01607 true 8.58159 0
* 81 59.49065 true 9.10423 1
* 96 51.65818 true 9.02102 0
* 99 17.55771 true 8.99762 0
*
*
* Remark
* ------
* - Relies on randomness of nextDouble() method in java.util.Random
* to generate pseudorandom numbers in [0, 1).
*
* - This library allows you to set and get the pseudorandom number seed.
*
* - See http://www.honeylocust.com/RngPack/ for an industrial
* strength random number generator in Java.
*
*************************************************************************/
import java.util.Random;
/**
* <i>Standard random</i>. This class provides methods for generating
* random number from various distributions.
* <p>
* For additional documentation, see <a href="http://introcs.cs.princeton.edu/22library">Section 2.2</a> of
* <i>Introduction to Programming in Java: An Interdisciplinary Approach</i> by Robert Sedgewick and Kevin Wayne.
*/
public final class StdRandom {
private static Random random; // pseudo-random number generator
private static long seed; // pseudo-random number generator seed
// static initializer
static {
// this is how the seed was set in Java 1.4
seed = System.currentTimeMillis();
random = new Random(seed);
}
// singleton pattern - can't instantiate
private StdRandom() { }
/**
* Set the seed of the psedurandom number generator.
*/
public static void setSeed(long s) {
seed = s;
random = new Random(seed);
}
/**
* Get the seed of the psedurandom number generator.
*/
public static long getSeed() {
return seed;
}
/**
* Return real number uniformly in [0, 1).
*/
public static double uniform() {
return random.nextDouble();
}
/**
* Return an integer uniformly between 0 and N-1.
*/
public static int uniform(int N) {
return random.nextInt(N);
}
///////////////////////////////////////////////////////////////////////////
// STATIC METHODS BELOW RELY ON JAVA.UTIL.RANDOM ONLY INDIRECTLY VIA
// THE STATIC METHODS ABOVE.
///////////////////////////////////////////////////////////////////////////
/**
* Return real number uniformly in [0, 1).
*/
public static double random() {
return uniform();
}
/**
* Return int uniformly in [a, b).
*/
public static int uniform(int a, int b) {
return a + uniform(b - a);
}
/**
* Return real number uniformly in [a, b).
*/
public static double uniform(double a, double b) {
return a + uniform() * (b-a);
}
/**
* Return a boolean, which is true with probability p, and false otherwise.
*/
public static boolean bernoulli(double p) {
return uniform() < p;
}
/**
* Return a boolean, which is true with probability .5, and false otherwise.
*/
public static boolean bernoulli() {
return bernoulli(0.5);
}
/**
* Return a real number with a standard Gaussian distribution.
*/
public static double gaussian() {
// use the polar form of the Box-Muller transform
double r, x, y;
do {
x = uniform(-1.0, 1.0);
y = uniform(-1.0, 1.0);
r = x*x + y*y;
} while (r >= 1 || r == 0);
return x * Math.sqrt(-2 * Math.log(r) / r);
// Remark: y * Math.sqrt(-2 * Math.log(r) / r)
// is an independent random gaussian
}
/**
* Return a real number from a gaussian distribution with given mean and stddev
*/
public static double gaussian(double mean, double stddev) {
return mean + stddev * gaussian();
}
/**
* Return an integer with a geometric distribution with mean 1/p.
*/
public static int geometric(double p) {
// using algorithm given by Knuth
return (int) Math.ceil(Math.log(uniform()) / Math.log(1.0 - p));
}
/**
* Return an integer with a Poisson distribution with mean lambda.
*/
public static int poisson(double lambda) {
// using algorithm given by Knuth
// see http://en.wikipedia.org/wiki/Poisson_distribution
int k = 0;
double p = 1.0;
double L = Math.exp(-lambda);
do {
k++;
p *= uniform();
} while (p >= L);
return k-1;
}
/**
* Return a real number with a Pareto distribution with parameter alpha.
*/
public static double pareto(double alpha) {
return Math.pow(1 - uniform(), -1.0/alpha) - 1.0;
}
/**
* Return a real number with a Cauchy distribution.
*/
public static double cauchy() {
return Math.tan(Math.PI * (uniform() - 0.5));
}
/**
* Return a number from a discrete distribution: i with probability a[i].
* Precondition: array entries are nonnegative and their sum equals 1.
*/
public static int discrete(double[] a) {
double EPSILON = 1E-14;
double sum = 0.0;
for (int i = 0; i < a.length; i++) {
if (a[i] < 0.0) throw new IllegalArgumentException("array entry " + i + " is negative: " + a[i]);
sum = sum + a[i];
}
if (sum > 1.0 + EPSILON || sum < 1.0 - EPSILON)
throw new IllegalArgumentException("sum of array entries not equal to one: " + sum);
double r = uniform();
sum = 0.0;
for (int i = 0; i < a.length; i++) {
sum = sum + a[i];
if (sum >= r) return i;
}
return -1;
}
/**
* Return a real number from an exponential distribution with rate lambda.
*/
public static double exp(double lambda) {
return -Math.log(1 - uniform()) / lambda;
}
/**
* Rearrange the elements of an array in random order.
*/
public static void shuffle(Object[] a) {
int N = a.length;
for (int i = 0; i < N; i++) {
int r = i + uniform(N-i); // between i and N-1
Object temp = a[i];
a[i] = a[r];
a[r] = temp;
}
}
/**
* Rearrange the elements of a double array in random order.
*/
public static void shuffle(double[] a) {
int N = a.length;
for (int i = 0; i < N; i++) {
int r = i + uniform(N-i); // between i and N-1
double temp = a[i];
a[i] = a[r];
a[r] = temp;
}
}
/**
* Rearrange the elements of an int array in random order.
*/
public static void shuffle(int[] a) {
int N = a.length;
for (int i = 0; i < N; i++) {
int r = i + uniform(N-i); // between i and N-1
int temp = a[i];
a[i] = a[r];
a[r] = temp;
}
}
/**
* Rearrange the elements of the subarray a[lo..hi] in random order.
*/
public static void shuffle(Object[] a, int lo, int hi) {
if (lo < 0 || lo > hi || hi >= a.length)
throw new RuntimeException("Illegal subarray range");
for (int i = lo; i <= hi; i++) {
int r = i + uniform(hi-i+1); // between i and hi
Object temp = a[i];
a[i] = a[r];
a[r] = temp;
}
}
/**
* Rearrange the elements of the subarray a[lo..hi] in random order.
*/
public static void shuffle(double[] a, int lo, int hi) {
if (lo < 0 || lo > hi || hi >= a.length)
throw new RuntimeException("Illegal subarray range");
for (int i = lo; i <= hi; i++) {
int r = i + uniform(hi-i+1); // between i and hi
double temp = a[i];
a[i] = a[r];
a[r] = temp;
}
}
/**
* Rearrange the elements of the subarray a[lo..hi] in random order.
*/
public static void shuffle(int[] a, int lo, int hi) {
if (lo < 0 || lo > hi || hi >= a.length)
throw new RuntimeException("Illegal subarray range");
for (int i = lo; i <= hi; i++) {
int r = i + uniform(hi-i+1); // between i and hi
int temp = a[i];
a[i] = a[r];
a[r] = temp;
}
}
/**
* Uniformly sample (without replacement) M of the N items from the array a[].
* To make it work with an Object[] argument and return an array of the
* underlying argument type requires some Java minutiae, e.g., using static
* generics and Arrays.copyOf().
*/
public static String[] sample(String[] a, int M) {
int N = a.length;
if (M < 0 || M > N)
throw new RuntimeException("Illegal number of samples");
String[] b = new String[M];
for (int i = 0; i < N; i++) {
int r = uniform(i+1); // between 0 and i
if (r < M) {
if (i < M) b[i] = b[r];
b[r] = a[i];
}
}
return b;
}
/**
* Unit test.
*/
public static void main(String[] args) {
int N = Integer.parseInt(args[0]);
if (args.length == 2) StdRandom.setSeed(Long.parseLong(args[1]));
double[] t = { .5, .3, .1, .1 };
StdOut.println("seed = " + StdRandom.getSeed());
for (int i = 0; i < N; i++) {
StdOut.printf("%2d " , uniform(100));
StdOut.printf("%8.5f ", uniform(10.0, 99.0));
StdOut.printf("%5b " , bernoulli(.5));
StdOut.printf("%7.5f ", gaussian(9.0, .2));
StdOut.printf("%2d " , discrete(t));
StdOut.println();
}
String[] a = "A B C D E F G".split(" ");
for (String s : a)
StdOut.print(s + " ");
StdOut.println();
String[] b = StdRandom.sample(a, 3);
for (String s : b)
StdOut.print(s + " ");
StdOut.println();
}
}
``` | 2012/08/24 | [
"https://Stackoverflow.com/questions/12104391",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/225998/"
] | You don't instantiate it, you call the methods statically:
```
StdRandom.setSeed(42L);
double n = StdRandom.uniform(66);
```
etc. | This is 'util' class with hidden constructor. Instead of create new instance call methods directly: `StdRandom.uniform(100)`, `StdRandom.random()`, etc.. |
13,121,850 | I have used will\_paginate in my rails application but i come across a situation where i need to use to will\_paginate inside a block where the page should not reload when i click the pagination number, could anyone help me saying how to integrate will\_paginate with ajax to avoid page reloading......? | 2012/10/29 | [
"https://Stackoverflow.com/questions/13121850",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/917833/"
] | I have a pagination javascript file
So in my index.html.erb file I addded
```
<%=javascript_include_tag "pagination.js"%>
```
In pagination.js file
```
$(function(){
$(".pagination a").live("click", function() {
$.get(this.href, null, null, "script");
return false;
});
});
```
I fetched the model data like this in the index action.
```
@employees = Employee.where("!is_deleted=?",1).paginate(:page=>params[:page] ,:per_page => 20)
```
and added this in the index.js.erb file
```
$("#employee_table").html("<%= escape_javascript(render("employees")) %>");
```
Here employee\_table is the id of the div where im displaying the data.
I have a file name will\_paginate\_array\_fix.rb in the config/initializers.
This file will look like this
```
require 'will_paginate/array'
```
Thats why even though i use where it works because it supports for arrays also. | Here is how I set up things:
Let assume I have an `Item` model.
First in the index view, I render a partial where pagination is performed:
```
<div id="list">
<%= render 'items/paginate_list', :items => @items %>
</div>
```
In the partial, I add a css class to my `will_paginate` statement:
```
items/_paginate_list.html.erb
<%= will_paginate items, :param_name => :page, :class => 'my_pagination' %>
# code displaying each item...
```
Then in the application.js, I catched events of clicking on the links of `my_pagination` class:
```
$(document).ready(function(){
$('.my_pagination a').live("click",function(){
$('.my_pagination').html('Page is loading, please wait...');
$.get(this.href, null, null, 'script');
return false;
});
});
```
This way the call is performed to the controller in ajax through the `$.get` statement. The pagination bar displays a message that page is loading.
In the controller, I just have the usual:
```
class ItemsController < ApplicationController
def index
@items=Item.paginate(:page => params[:page], :per_page => 10)
end
end
```
Finally, in the embedded js, I feed the partial with pagination to be reloaded:
```
items/index.js.erb
$("#list").html("<%= escape_javascript(render 'items/paginate_list', :items => @items) %>");
```
Hope this help.
Actually, It is roughly a quick summary of the [railscast](http://railscasts.com/episodes/174-pagination-with-ajax?view=asciicast) ;-) |
8,322,550 | I've installed XAMPP on my Windows XP. I started the XAMPP control panel and it shows apache and mysql are running.
When I check the status by going to `localhost/xampp` it shows:
```
mysql : deactivated
```
When I run php files that access the mysql database, it shows the following errors:
```
Warning: mysql_connect() [function.mysql-connect]: [2002] No connection could
be made because the target machine actively refused it. (trying to connect
via tcp://localhost:3306) in C:\xampp\htdocs\Elo_algorithm.php on
line 18
```
I've been through the XAMPP troubleshooting page and FAQ but I don't understand what to do. The XAMPP control panel shows mysql is running, but xampp status shows: `deactivated`.
What is going on here? | 2011/11/30 | [
"https://Stackoverflow.com/questions/8322550",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/1029133/"
] | You should view in the xampp installation the file "\xampp\mysql\data\mysql\_error.log".
This file contais the error log of MySQL and in it you can detect any problem like por in use.
For example, this lines of log show that the port 3306 (the mysql default) is used by another application and can't be accessed.
```
111130 8:39:56 [ERROR] Can't start server: Bind on TCP/IP port: No such file or directory
111130 8:39:56 [ERROR] Do you already have another mysqld server running on port: 3306 ?
111130 8:39:56 [ERROR] Aborting
```
If all in the MySQL is correct probably the problem is related to the driver in the php application. Currently PHP has two MySQL connector types, the "mysql" and the "mysqli", MySQL "mysql" connector, that use "**mysql\_**" (the method that you are using to connect is mysql\_connect) prefixed functions, is used for old MySQL 4 applications and when the MySQL 5.x if is in configured with the "old password" parameter. The "mysqli" is used for the new mysql 5.x versions and in php you must use "**mysqli\_**" prefixed functions like "mysqli\_connect.
The version used by the lastest versions of xampp is MySQL 5.5 and you require to used the mysqli connector. | Check whether the value of port variable in the "my.ini" file in your xampp mysql folder is 3306 or 8888 |
8,322,550 | I've installed XAMPP on my Windows XP. I started the XAMPP control panel and it shows apache and mysql are running.
When I check the status by going to `localhost/xampp` it shows:
```
mysql : deactivated
```
When I run php files that access the mysql database, it shows the following errors:
```
Warning: mysql_connect() [function.mysql-connect]: [2002] No connection could
be made because the target machine actively refused it. (trying to connect
via tcp://localhost:3306) in C:\xampp\htdocs\Elo_algorithm.php on
line 18
```
I've been through the XAMPP troubleshooting page and FAQ but I don't understand what to do. The XAMPP control panel shows mysql is running, but xampp status shows: `deactivated`.
What is going on here? | 2011/11/30 | [
"https://Stackoverflow.com/questions/8322550",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/1029133/"
] | You should view in the xampp installation the file "\xampp\mysql\data\mysql\_error.log".
This file contais the error log of MySQL and in it you can detect any problem like por in use.
For example, this lines of log show that the port 3306 (the mysql default) is used by another application and can't be accessed.
```
111130 8:39:56 [ERROR] Can't start server: Bind on TCP/IP port: No such file or directory
111130 8:39:56 [ERROR] Do you already have another mysqld server running on port: 3306 ?
111130 8:39:56 [ERROR] Aborting
```
If all in the MySQL is correct probably the problem is related to the driver in the php application. Currently PHP has two MySQL connector types, the "mysql" and the "mysqli", MySQL "mysql" connector, that use "**mysql\_**" (the method that you are using to connect is mysql\_connect) prefixed functions, is used for old MySQL 4 applications and when the MySQL 5.x if is in configured with the "old password" parameter. The "mysqli" is used for the new mysql 5.x versions and in php you must use "**mysqli\_**" prefixed functions like "mysqli\_connect.
The version used by the lastest versions of xampp is MySQL 5.5 and you require to used the mysqli connector. | i was facing the same problem. I had to run setup-xampp.bat to make it working.
By the way I came across a new WAMP stack called AMPPS. It looks quite easier than XAMP. You should try. <http://www.ampps.com> |
8,322,550 | I've installed XAMPP on my Windows XP. I started the XAMPP control panel and it shows apache and mysql are running.
When I check the status by going to `localhost/xampp` it shows:
```
mysql : deactivated
```
When I run php files that access the mysql database, it shows the following errors:
```
Warning: mysql_connect() [function.mysql-connect]: [2002] No connection could
be made because the target machine actively refused it. (trying to connect
via tcp://localhost:3306) in C:\xampp\htdocs\Elo_algorithm.php on
line 18
```
I've been through the XAMPP troubleshooting page and FAQ but I don't understand what to do. The XAMPP control panel shows mysql is running, but xampp status shows: `deactivated`.
What is going on here? | 2011/11/30 | [
"https://Stackoverflow.com/questions/8322550",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/1029133/"
] | OK I got this issue resolved in my case, hopefully will help you too. Problem was system itself. If you run Vista, Win7, win8 you probably have permission issue. Simple go to XAMPP root and find mysql\_start.bat and run it. Immediately after clicking your firewall will appear with message asking for permission. All you have to do is to allow permission (for private networks such a home or work network).
MySQL database ACTIVATED - and that's what matters ;)
I hope that helps to all of you who did not get an answer so far.
Cheers! | You should view in the xampp installation the file "\xampp\mysql\data\mysql\_error.log".
This file contais the error log of MySQL and in it you can detect any problem like por in use.
For example, this lines of log show that the port 3306 (the mysql default) is used by another application and can't be accessed.
```
111130 8:39:56 [ERROR] Can't start server: Bind on TCP/IP port: No such file or directory
111130 8:39:56 [ERROR] Do you already have another mysqld server running on port: 3306 ?
111130 8:39:56 [ERROR] Aborting
```
If all in the MySQL is correct probably the problem is related to the driver in the php application. Currently PHP has two MySQL connector types, the "mysql" and the "mysqli", MySQL "mysql" connector, that use "**mysql\_**" (the method that you are using to connect is mysql\_connect) prefixed functions, is used for old MySQL 4 applications and when the MySQL 5.x if is in configured with the "old password" parameter. The "mysqli" is used for the new mysql 5.x versions and in php you must use "**mysqli\_**" prefixed functions like "mysqli\_connect.
The version used by the lastest versions of xampp is MySQL 5.5 and you require to used the mysqli connector. |
8,322,550 | I've installed XAMPP on my Windows XP. I started the XAMPP control panel and it shows apache and mysql are running.
When I check the status by going to `localhost/xampp` it shows:
```
mysql : deactivated
```
When I run php files that access the mysql database, it shows the following errors:
```
Warning: mysql_connect() [function.mysql-connect]: [2002] No connection could
be made because the target machine actively refused it. (trying to connect
via tcp://localhost:3306) in C:\xampp\htdocs\Elo_algorithm.php on
line 18
```
I've been through the XAMPP troubleshooting page and FAQ but I don't understand what to do. The XAMPP control panel shows mysql is running, but xampp status shows: `deactivated`.
What is going on here? | 2011/11/30 | [
"https://Stackoverflow.com/questions/8322550",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/1029133/"
] | You should view in the xampp installation the file "\xampp\mysql\data\mysql\_error.log".
This file contais the error log of MySQL and in it you can detect any problem like por in use.
For example, this lines of log show that the port 3306 (the mysql default) is used by another application and can't be accessed.
```
111130 8:39:56 [ERROR] Can't start server: Bind on TCP/IP port: No such file or directory
111130 8:39:56 [ERROR] Do you already have another mysqld server running on port: 3306 ?
111130 8:39:56 [ERROR] Aborting
```
If all in the MySQL is correct probably the problem is related to the driver in the php application. Currently PHP has two MySQL connector types, the "mysql" and the "mysqli", MySQL "mysql" connector, that use "**mysql\_**" (the method that you are using to connect is mysql\_connect) prefixed functions, is used for old MySQL 4 applications and when the MySQL 5.x if is in configured with the "old password" parameter. The "mysqli" is used for the new mysql 5.x versions and in php you must use "**mysqli\_**" prefixed functions like "mysqli\_connect.
The version used by the lastest versions of xampp is MySQL 5.5 and you require to used the mysqli connector. | I could not get XAMPP for Windows (1.7.4 Beta2--I know; ancient) to work on Windows 7 (32 bit) as the MySql would not "activate" or connect to Apache. Just by dumb luck I installed .NET Framework 4.6 for another application and suddenly--Whoopee! It started working! |
8,322,550 | I've installed XAMPP on my Windows XP. I started the XAMPP control panel and it shows apache and mysql are running.
When I check the status by going to `localhost/xampp` it shows:
```
mysql : deactivated
```
When I run php files that access the mysql database, it shows the following errors:
```
Warning: mysql_connect() [function.mysql-connect]: [2002] No connection could
be made because the target machine actively refused it. (trying to connect
via tcp://localhost:3306) in C:\xampp\htdocs\Elo_algorithm.php on
line 18
```
I've been through the XAMPP troubleshooting page and FAQ but I don't understand what to do. The XAMPP control panel shows mysql is running, but xampp status shows: `deactivated`.
What is going on here? | 2011/11/30 | [
"https://Stackoverflow.com/questions/8322550",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/1029133/"
] | OK I got this issue resolved in my case, hopefully will help you too. Problem was system itself. If you run Vista, Win7, win8 you probably have permission issue. Simple go to XAMPP root and find mysql\_start.bat and run it. Immediately after clicking your firewall will appear with message asking for permission. All you have to do is to allow permission (for private networks such a home or work network).
MySQL database ACTIVATED - and that's what matters ;)
I hope that helps to all of you who did not get an answer so far.
Cheers! | Check whether the value of port variable in the "my.ini" file in your xampp mysql folder is 3306 or 8888 |
8,322,550 | I've installed XAMPP on my Windows XP. I started the XAMPP control panel and it shows apache and mysql are running.
When I check the status by going to `localhost/xampp` it shows:
```
mysql : deactivated
```
When I run php files that access the mysql database, it shows the following errors:
```
Warning: mysql_connect() [function.mysql-connect]: [2002] No connection could
be made because the target machine actively refused it. (trying to connect
via tcp://localhost:3306) in C:\xampp\htdocs\Elo_algorithm.php on
line 18
```
I've been through the XAMPP troubleshooting page and FAQ but I don't understand what to do. The XAMPP control panel shows mysql is running, but xampp status shows: `deactivated`.
What is going on here? | 2011/11/30 | [
"https://Stackoverflow.com/questions/8322550",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/1029133/"
] | OK I got this issue resolved in my case, hopefully will help you too. Problem was system itself. If you run Vista, Win7, win8 you probably have permission issue. Simple go to XAMPP root and find mysql\_start.bat and run it. Immediately after clicking your firewall will appear with message asking for permission. All you have to do is to allow permission (for private networks such a home or work network).
MySQL database ACTIVATED - and that's what matters ;)
I hope that helps to all of you who did not get an answer so far.
Cheers! | i was facing the same problem. I had to run setup-xampp.bat to make it working.
By the way I came across a new WAMP stack called AMPPS. It looks quite easier than XAMP. You should try. <http://www.ampps.com> |
8,322,550 | I've installed XAMPP on my Windows XP. I started the XAMPP control panel and it shows apache and mysql are running.
When I check the status by going to `localhost/xampp` it shows:
```
mysql : deactivated
```
When I run php files that access the mysql database, it shows the following errors:
```
Warning: mysql_connect() [function.mysql-connect]: [2002] No connection could
be made because the target machine actively refused it. (trying to connect
via tcp://localhost:3306) in C:\xampp\htdocs\Elo_algorithm.php on
line 18
```
I've been through the XAMPP troubleshooting page and FAQ but I don't understand what to do. The XAMPP control panel shows mysql is running, but xampp status shows: `deactivated`.
What is going on here? | 2011/11/30 | [
"https://Stackoverflow.com/questions/8322550",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/1029133/"
] | OK I got this issue resolved in my case, hopefully will help you too. Problem was system itself. If you run Vista, Win7, win8 you probably have permission issue. Simple go to XAMPP root and find mysql\_start.bat and run it. Immediately after clicking your firewall will appear with message asking for permission. All you have to do is to allow permission (for private networks such a home or work network).
MySQL database ACTIVATED - and that's what matters ;)
I hope that helps to all of you who did not get an answer so far.
Cheers! | I could not get XAMPP for Windows (1.7.4 Beta2--I know; ancient) to work on Windows 7 (32 bit) as the MySql would not "activate" or connect to Apache. Just by dumb luck I installed .NET Framework 4.6 for another application and suddenly--Whoopee! It started working! |
22,690,091 | I need to create simple icon in css like this - about 32x32 px.
I'd like to make it as simple as it could be (html - no unnecessary divs). The text should be vertically and horizontally aligned to the center of each half.
The text displayed will be short (about 9 chars max, font-size about 10px). It should have static height and width. ALSO The text has to be written in tags (like or ) so it'd be accessible by CMS.
Here is my solution, which I find wrong, because the height and width is not static:
jsfiddle.net/s2DRr/1/ | 2014/03/27 | [
"https://Stackoverflow.com/questions/22690091",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/3151531/"
] | What's Going On
---------------
I use the `i` element to create icons. Normally with an image, or more recently an icon font, but we can adapt for your needs. (Originally the `i` element wasn't used for icon, and it is debatable whether it's semantically correct. However, it's used in many icon fonts, and in some major websites.) Since you need to be able to dynamically place the content in the HTML, we can use the `i` as a wrap, and a `div` inside to make the second color.
Code
----
[**Working Fiddle**](http://jsfiddle.net/hyJLz/)
### HTML:
```
<i>Top<div>Bottom</div></i>
```
### CSS:
```
i {
height:32px;
width:32px;
display:inline-block;
position:relative;
color:white;
font-size:10px;
background:lightgreen;
text-align:center;
font-style:normal;
}
i div {
background:orange;
position:absolute;
bottom:0;
height:50%;
width:100%;
}
```
Screenshot
----------
 | You may need to alter the below to match your requirements better, but it should give you a decent starting point:
[Sample Fiddle](http://jsfiddle.net/swfour/CkAS3/1/)
====================================================
HTML
```
<i></i>
```
CSS
```
i {
height:32px;
width:32px;
display:inline-block;
position:relative;
color:white;
font-size:10px;
}
i:before, i:after {
display:block;
height:16px;
width:32px;
text-align:center;
padding-top:2px;
overflow:hidden;
box-sizing:border-box;
}
i:before {
content:'text1';
background:lightgreen;
}
i:after {
content:'text2';
background:orange;
position:absolute;
bottom:0;
}
``` |
3,439,265 | I have installed oracle 10g express edition and I did not find the option to
create schema..
Is there a option to create schema in oracle 10g express edition
or else I have to install other oracle 10g..?
To create schema which oracle 10g
I have to install... what? | 2010/08/09 | [
"https://Stackoverflow.com/questions/3439265",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/396486/"
] | You don't need to explicitly create schema, Oracle automatically creates a schema when you create a user (see **[`CREATE USER`](http://download.oracle.com/docs/cd/B13789_01/server.101/b10759/statements_8003.htm#i2065278)** documentation).
If you really want, you can use [**`CREATE SCHEMA`**](http://download.oracle.com/docs/cd/B13789_01/server.101/b10759/statements_6013.htm) statement and issue it through Oracle Express web interface or from SQL prompt. | As zendar said, creating a user automatically creates their schema (in Oracle these are pretty much the same concept).
When you create a Workspace in apex, it will ask you if you want to use an existing schema or create a new one - so that's another easy option you could use. |
3,439,265 | I have installed oracle 10g express edition and I did not find the option to
create schema..
Is there a option to create schema in oracle 10g express edition
or else I have to install other oracle 10g..?
To create schema which oracle 10g
I have to install... what? | 2010/08/09 | [
"https://Stackoverflow.com/questions/3439265",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/396486/"
] | You don't need to explicitly create schema, Oracle automatically creates a schema when you create a user (see **[`CREATE USER`](http://download.oracle.com/docs/cd/B13789_01/server.101/b10759/statements_8003.htm#i2065278)** documentation).
If you really want, you can use [**`CREATE SCHEMA`**](http://download.oracle.com/docs/cd/B13789_01/server.101/b10759/statements_6013.htm) statement and issue it through Oracle Express web interface or from SQL prompt. | The `CREATE SCHEMA` statement can include `CREATE TABLE`, `CREATE VIEW`, and `GRANT` statements. To issue a `CREATE SCHEMA` statement, you must have the privileges necessary to issue the included statements.
```
CREATE SCHEMA AUTHORIZATION oe
CREATE TABLE new_product
(color VARCHAR2(10) PRIMARY KEY, quantity NUMBER)
CREATE VIEW new_product_view
AS SELECT color, quantity FROM new_product WHERE color = 'RED'
GRANT select ON new_product_view TO hr;
``` |
3,439,265 | I have installed oracle 10g express edition and I did not find the option to
create schema..
Is there a option to create schema in oracle 10g express edition
or else I have to install other oracle 10g..?
To create schema which oracle 10g
I have to install... what? | 2010/08/09 | [
"https://Stackoverflow.com/questions/3439265",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/396486/"
] | The `CREATE SCHEMA` statement can include `CREATE TABLE`, `CREATE VIEW`, and `GRANT` statements. To issue a `CREATE SCHEMA` statement, you must have the privileges necessary to issue the included statements.
```
CREATE SCHEMA AUTHORIZATION oe
CREATE TABLE new_product
(color VARCHAR2(10) PRIMARY KEY, quantity NUMBER)
CREATE VIEW new_product_view
AS SELECT color, quantity FROM new_product WHERE color = 'RED'
GRANT select ON new_product_view TO hr;
``` | As zendar said, creating a user automatically creates their schema (in Oracle these are pretty much the same concept).
When you create a Workspace in apex, it will ask you if you want to use an existing schema or create a new one - so that's another easy option you could use. |
46,328,375 | I have been following Gorail's tutorial to deploy on DigitalOcean. [See Here](https://gorails.com/deploy/ubuntu/16.04#capistrano) and [Here also](https://www.youtube.com/watch?time_continue=467&v=WBPV4vjzcjQ).
I've reached the part where I am using the cap production deploy in the command line, but I am getting the following error below, I am not understanding how this error is occuring:
```
luis@luis-Inspiron-7559:~/Desktop/mls2$ cap production deploy --trace
cap aborted!
LoadError: cannot load such file -- capistrano/rbenv
/usr/local/lib/site_ruby/2.4.0/rubygems/core_ext/kernel_require.rb:55:in `require'
/usr/local/lib/site_ruby/2.4.0/rubygems/core_ext/kernel_require.rb:55:in `require'
/home/luis/Desktop/mls2/Capfile:31:in `<top (required)>'
/usr/lib/ruby/vendor_ruby/rake/rake_module.rb:28:in `load'
/usr/lib/ruby/vendor_ruby/rake/rake_module.rb:28:in `load_rakefile'
/usr/lib/ruby/vendor_ruby/rake/application.rb:689:in `raw_load_rakefile'
/usr/lib/ruby/vendor_ruby/rake/application.rb:94:in `block in load_rakefile'
/usr/lib/ruby/vendor_ruby/rake/application.rb:176:in `standard_exception_handling'
/usr/lib/ruby/vendor_ruby/rake/application.rb:93:in `load_rakefile'
/usr/lib/ruby/vendor_ruby/rake/application.rb:77:in `block in run'
/usr/lib/ruby/vendor_ruby/rake/application.rb:176:in `standard_exception_handling'
/usr/lib/ruby/vendor_ruby/rake/application.rb:75:in `run'
/usr/lib/ruby/vendor_ruby/capistrano/application.rb:15:in `run'
/usr/bin/cap:3:in `<main>'
```
This is my cap file:
```
# Load DSL and set up stages
require "capistrano/setup"
# Include default deployment tasks
require "capistrano/deploy"
# Load the SCM plugin appropriate to your project:
#
# require "capistrano/scm/hg"
# install_plugin Capistrano::SCM::Hg
# or
# require "capistrano/scm/svn"
# install_plugin Capistrano::SCM::Svn
# or
# require "capistrano/scm/git"
# install_plugin Capistrano::SCM::Git
# Include tasks from other gems included in your Gemfile
#
# For documentation on these, see for example:
#
# https://github.com/capistrano/rvm
# https://github.com/capistrano/rbenv
# https://github.com/capistrano/chruby
# https://github.com/capistrano/bundler
# https://github.com/capistrano/rails
# https://github.com/capistrano/passenger
#
# require "capistrano/rvm"
require "capistrano/rbenv"
set :rbenv_type, :user
set :rbenv_ruby, '2.4.1'
require "capistrano/bundler"
require 'capistrano/rails'
# require "capistrano/chruby"
# require "capistrano/rails/assets"
# require "capistrano/rails/migrations"
# require "capistrano/passenger"
# Load custom tasks from `lib/capistrano/tasks` if you have any defined
Dir.glob("lib/capistrano/tasks/*.rake").each { |r| import r }
```
and my production.rb :
```
set :production
server 'xxx.xxx.xxx.xxx', user: 'USER', roles: %w{app db web}
```
and my gemfile, i've already added the capistrano gems in the development group as suggested in the video:
```
...
group :development do
# Access an IRB console on exception pages or by using <%= console %> anywhere in the code.
gem 'web-console', '>= 3.3.0'
gem 'listen', '~> 3.0.5'
# Spring speeds up development by keeping your application running in the background. Read more: https://github.com/rails/spring
gem 'spring'
gem 'spring-watcher-listen', '~> 2.0.0'
gem 'capistrano', '~> 3.9', '>= 3.9.1'
gem 'capistrano-rails', '~> 1.3'
gem 'capistrano-passenger', '~> 0.2.0'
gem 'capistrano-rbenv', '~> 2.1', '>= 2.1.1'
end
...
``` | 2017/09/20 | [
"https://Stackoverflow.com/questions/46328375",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/7438959/"
] | You need to install [that dependency](https://github.com/capistrano/rbenv) by adding it to your `Gemfile`:
```
gem 'capistrano-rbenv'
```
Then `bundle install`.
Capistrano has started to shunt some of the lesser used features to optional modules lately. | Run Capistrano with `bundle exec cap production deploy`, in addition to making sure that the `capistrano-rbenv` gem is in your Gemfile, and `capistrano/rbenv` is in your Capfile as outlined in the other answers. |
46,328,375 | I have been following Gorail's tutorial to deploy on DigitalOcean. [See Here](https://gorails.com/deploy/ubuntu/16.04#capistrano) and [Here also](https://www.youtube.com/watch?time_continue=467&v=WBPV4vjzcjQ).
I've reached the part where I am using the cap production deploy in the command line, but I am getting the following error below, I am not understanding how this error is occuring:
```
luis@luis-Inspiron-7559:~/Desktop/mls2$ cap production deploy --trace
cap aborted!
LoadError: cannot load such file -- capistrano/rbenv
/usr/local/lib/site_ruby/2.4.0/rubygems/core_ext/kernel_require.rb:55:in `require'
/usr/local/lib/site_ruby/2.4.0/rubygems/core_ext/kernel_require.rb:55:in `require'
/home/luis/Desktop/mls2/Capfile:31:in `<top (required)>'
/usr/lib/ruby/vendor_ruby/rake/rake_module.rb:28:in `load'
/usr/lib/ruby/vendor_ruby/rake/rake_module.rb:28:in `load_rakefile'
/usr/lib/ruby/vendor_ruby/rake/application.rb:689:in `raw_load_rakefile'
/usr/lib/ruby/vendor_ruby/rake/application.rb:94:in `block in load_rakefile'
/usr/lib/ruby/vendor_ruby/rake/application.rb:176:in `standard_exception_handling'
/usr/lib/ruby/vendor_ruby/rake/application.rb:93:in `load_rakefile'
/usr/lib/ruby/vendor_ruby/rake/application.rb:77:in `block in run'
/usr/lib/ruby/vendor_ruby/rake/application.rb:176:in `standard_exception_handling'
/usr/lib/ruby/vendor_ruby/rake/application.rb:75:in `run'
/usr/lib/ruby/vendor_ruby/capistrano/application.rb:15:in `run'
/usr/bin/cap:3:in `<main>'
```
This is my cap file:
```
# Load DSL and set up stages
require "capistrano/setup"
# Include default deployment tasks
require "capistrano/deploy"
# Load the SCM plugin appropriate to your project:
#
# require "capistrano/scm/hg"
# install_plugin Capistrano::SCM::Hg
# or
# require "capistrano/scm/svn"
# install_plugin Capistrano::SCM::Svn
# or
# require "capistrano/scm/git"
# install_plugin Capistrano::SCM::Git
# Include tasks from other gems included in your Gemfile
#
# For documentation on these, see for example:
#
# https://github.com/capistrano/rvm
# https://github.com/capistrano/rbenv
# https://github.com/capistrano/chruby
# https://github.com/capistrano/bundler
# https://github.com/capistrano/rails
# https://github.com/capistrano/passenger
#
# require "capistrano/rvm"
require "capistrano/rbenv"
set :rbenv_type, :user
set :rbenv_ruby, '2.4.1'
require "capistrano/bundler"
require 'capistrano/rails'
# require "capistrano/chruby"
# require "capistrano/rails/assets"
# require "capistrano/rails/migrations"
# require "capistrano/passenger"
# Load custom tasks from `lib/capistrano/tasks` if you have any defined
Dir.glob("lib/capistrano/tasks/*.rake").each { |r| import r }
```
and my production.rb :
```
set :production
server 'xxx.xxx.xxx.xxx', user: 'USER', roles: %w{app db web}
```
and my gemfile, i've already added the capistrano gems in the development group as suggested in the video:
```
...
group :development do
# Access an IRB console on exception pages or by using <%= console %> anywhere in the code.
gem 'web-console', '>= 3.3.0'
gem 'listen', '~> 3.0.5'
# Spring speeds up development by keeping your application running in the background. Read more: https://github.com/rails/spring
gem 'spring'
gem 'spring-watcher-listen', '~> 2.0.0'
gem 'capistrano', '~> 3.9', '>= 3.9.1'
gem 'capistrano-rails', '~> 1.3'
gem 'capistrano-passenger', '~> 0.2.0'
gem 'capistrano-rbenv', '~> 2.1', '>= 2.1.1'
end
...
``` | 2017/09/20 | [
"https://Stackoverflow.com/questions/46328375",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/7438959/"
] | You forgot to require capistrano/passenger in your Capfile. | Run Capistrano with `bundle exec cap production deploy`, in addition to making sure that the `capistrano-rbenv` gem is in your Gemfile, and `capistrano/rbenv` is in your Capfile as outlined in the other answers. |
46,328,375 | I have been following Gorail's tutorial to deploy on DigitalOcean. [See Here](https://gorails.com/deploy/ubuntu/16.04#capistrano) and [Here also](https://www.youtube.com/watch?time_continue=467&v=WBPV4vjzcjQ).
I've reached the part where I am using the cap production deploy in the command line, but I am getting the following error below, I am not understanding how this error is occuring:
```
luis@luis-Inspiron-7559:~/Desktop/mls2$ cap production deploy --trace
cap aborted!
LoadError: cannot load such file -- capistrano/rbenv
/usr/local/lib/site_ruby/2.4.0/rubygems/core_ext/kernel_require.rb:55:in `require'
/usr/local/lib/site_ruby/2.4.0/rubygems/core_ext/kernel_require.rb:55:in `require'
/home/luis/Desktop/mls2/Capfile:31:in `<top (required)>'
/usr/lib/ruby/vendor_ruby/rake/rake_module.rb:28:in `load'
/usr/lib/ruby/vendor_ruby/rake/rake_module.rb:28:in `load_rakefile'
/usr/lib/ruby/vendor_ruby/rake/application.rb:689:in `raw_load_rakefile'
/usr/lib/ruby/vendor_ruby/rake/application.rb:94:in `block in load_rakefile'
/usr/lib/ruby/vendor_ruby/rake/application.rb:176:in `standard_exception_handling'
/usr/lib/ruby/vendor_ruby/rake/application.rb:93:in `load_rakefile'
/usr/lib/ruby/vendor_ruby/rake/application.rb:77:in `block in run'
/usr/lib/ruby/vendor_ruby/rake/application.rb:176:in `standard_exception_handling'
/usr/lib/ruby/vendor_ruby/rake/application.rb:75:in `run'
/usr/lib/ruby/vendor_ruby/capistrano/application.rb:15:in `run'
/usr/bin/cap:3:in `<main>'
```
This is my cap file:
```
# Load DSL and set up stages
require "capistrano/setup"
# Include default deployment tasks
require "capistrano/deploy"
# Load the SCM plugin appropriate to your project:
#
# require "capistrano/scm/hg"
# install_plugin Capistrano::SCM::Hg
# or
# require "capistrano/scm/svn"
# install_plugin Capistrano::SCM::Svn
# or
# require "capistrano/scm/git"
# install_plugin Capistrano::SCM::Git
# Include tasks from other gems included in your Gemfile
#
# For documentation on these, see for example:
#
# https://github.com/capistrano/rvm
# https://github.com/capistrano/rbenv
# https://github.com/capistrano/chruby
# https://github.com/capistrano/bundler
# https://github.com/capistrano/rails
# https://github.com/capistrano/passenger
#
# require "capistrano/rvm"
require "capistrano/rbenv"
set :rbenv_type, :user
set :rbenv_ruby, '2.4.1'
require "capistrano/bundler"
require 'capistrano/rails'
# require "capistrano/chruby"
# require "capistrano/rails/assets"
# require "capistrano/rails/migrations"
# require "capistrano/passenger"
# Load custom tasks from `lib/capistrano/tasks` if you have any defined
Dir.glob("lib/capistrano/tasks/*.rake").each { |r| import r }
```
and my production.rb :
```
set :production
server 'xxx.xxx.xxx.xxx', user: 'USER', roles: %w{app db web}
```
and my gemfile, i've already added the capistrano gems in the development group as suggested in the video:
```
...
group :development do
# Access an IRB console on exception pages or by using <%= console %> anywhere in the code.
gem 'web-console', '>= 3.3.0'
gem 'listen', '~> 3.0.5'
# Spring speeds up development by keeping your application running in the background. Read more: https://github.com/rails/spring
gem 'spring'
gem 'spring-watcher-listen', '~> 2.0.0'
gem 'capistrano', '~> 3.9', '>= 3.9.1'
gem 'capistrano-rails', '~> 1.3'
gem 'capistrano-passenger', '~> 0.2.0'
gem 'capistrano-rbenv', '~> 2.1', '>= 2.1.1'
end
...
``` | 2017/09/20 | [
"https://Stackoverflow.com/questions/46328375",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/7438959/"
] | First, this is not directly causing your problem, but you have a mistake in your Capfile. If you look at [the official documentation for capistrano-rbenv](https://github.com/capistrano/rbenv#usage), the `set` commands are supposed to go in `deploy.rb`, not in `Capfile`. I suggest removing those lines and moving them to deploy.rb.
```
# Move to deploy.rb
set :rbenv_type, :user
set :rbenv_ruby, '2.4.1'
```
---
In any case, the error you are getting is likely due to the fact that the gem `capistrano-rbenv` can't be loaded. Here's what I would try:
1. Run `bundle exec cap production deploy`. All cap commands must be prefixed with `bundle exec`. Otherwise there is no guarantee that the Gemfile will be used.
2. If that doesn't work, run `bundle config without` to see if the `development` group of your Gemfile is being excluded by bundler. If so, remove that setting by running `bundle config --delete without`. | Run Capistrano with `bundle exec cap production deploy`, in addition to making sure that the `capistrano-rbenv` gem is in your Gemfile, and `capistrano/rbenv` is in your Capfile as outlined in the other answers. |
4,313,867 | What does `performSelector` do? What is the difference between creating a new `NSThread` and the `performSelector` method?
How it works and where should we use it? | 2010/11/30 | [
"https://Stackoverflow.com/questions/4313867",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/202735/"
] | All of these perform the same task, that is make the `doStuff` method on `anObject` execute synchronously on the **current** thread:
```
// 1
[anObject doStuff];
// 2
[anObject performSelector:@selector(doStuff)];
// 3
objc_msgSend(anObject, @selector(doStuff));
// 4
IMP imp = [anObject methodForSelector:@selector(doStuff)];
imp(anObject, @selector(doStuff));
```
1. Is how you normally should go about to do stuff.
2. Is for dynamically dispatching a message. Use if the selector is unknown, or provided by a client, for example if you implement an target-action pattern. or if the class of `anObject` is unknown, usually used by first asking if the object has the method with `-[NSObject respondsToSelector:]`.
3. Is what no 1. is actually compiled down to. Usually never any real need to do this.
4. Cached the actual `IMP` *(implementation)* for a method, and then call it directly. Can sometimes be faster than 1. if used in a tight loop. Just remember; *premature optimization is evil*.
What you need to grasp is that in Objective-C methods are more important than classes/interfaces. Usually you do not query an object if it belongs to a particular class, or conforms to any protocol, that is for the compiler to complain about. At run-time you instead query for specific methods.
In short: **It does not matter what you are, just what you can do.**
As a convenience `NSObject` also have several siblings to `performSelector` that are asynchronios. Most notably:
* `performSelector:withObject:afterDelay:` - To execute the method on the current thread after a delay.
* `performSelectorInBackground:withObject:` - To execute the method on a new background thread.
* `performSelectorOnMainThread:withObject:waitUntilDone:` - To execute the method on the main thread.
* `performSelector:onThread:withObject:waitUntilDone:` - To execute the method on any thread.
The asynchronous performers all depend on a `NSRunLoop` to function. This is not something you need to worry about unless you spawn a thread yourself. If you do then you need to also run the new threads run loop. Just skip that for now. | `performSelector` executes a selector. In other words, it calls a method.
It is very different from running a new thread.
I think it would be best for you to read up on [selectors](http://developer.apple.com/library/ios/#documentation/Cocoa/Conceptual/ObjectiveC/Articles/ocSelectors.html#//apple_ref/doc/uid/TP30001163-CH23-SW1). |
173,361 | With regards to Thermal Radiation, given a stable body initially at 300 Kelvin placed in isolation, after continuous Thermal Radiation will it's temperature gradually reduce to 0 kelvin asymptotically? If so, does this mean that the body is now devoid of any Thermal Energy? And does it imply that the only energy it can possibly have is (now) due to it's electronic structure? | 2015/03/31 | [
"https://physics.stackexchange.com/questions/173361",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/76641/"
] | In practice, no. In theory, also no.
The Universe is filled with photons with an energy distribution corresponding to $2.73\,\mathrm{K}$, called the [cosmic microwave background (CMB)](http://en.wikipedia.org/wiki/Cosmic_microwave_background). Every $\mathrm{cm}^3$ of space holds [around 400](https://physics.stackexchange.com/q/196366/70207) of them, so each second one $\mathrm{cm}^2$ is hit by roughly one hundred billion of these photons. That means that if you place your "stable body" in an ever-so-isolated box, the box itself will never come below $2.73\,\mathrm{K}$, and neither will the body inside. It will asymptotically go towards thermal equilibrium at $T = 2.73\,\mathrm{K}$.
Even if you magically removed everything else in the Universe but the body$^\dagger$, $0\,\mathrm{K}$ can never be reached. The reason is that this would imply zero motion of the atoms of the body, which is [forbidden by law](http://en.wikipedia.org/wiki/Uncertainty_principle).
In practice, it *is* actually possible to have temperatures lower than the 2.73 K of the CMB. When a gas expands, it cools, and if it expands faster than it can be heated by the CMB, it can temporarily reach lower temperatures. This is the case for the [Boomerang Nebula](http://en.wikipedia.org/wiki/Boomerang_Nebula), which has a temperature of 1 K. The nebula will probably be heated to the temperature of the CMB in around 10,000 years or so.
---
$^\dagger$Or waited billions of years for the CMB to cool. | It´s impossible to drop a body temperature to absolute 0K. You must notice that, at the same time the body is radiating energy from its own temperature, it is also receiving temperature from other sources (regardless the distance of the source) like distant stars. |
6,363,710 | I am new to Objective C. On one of the developers documentation, I found the following statemenet.
**The following statement invokes the lockFocusIfCanDraw method and assigns the return value to
flag. It does not generate a compiler warning unless there is a mismatch between the type for flag
and the method’s return type. Nonetheless, this pattern is strongly discouraged.**
```
flag = aView.lockFocusIfCanDraw;
```
In addition to the one above, I can think of many situations of this kind. For instance I might want to capture the display text from a box and assign it to a local string etc.
I am just wondering, if the above statement is discouraged, what is the recommended way of handling such situation? | 2011/06/15 | [
"https://Stackoverflow.com/questions/6363710",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/402814/"
] | The dot syntax for calling methods should only be used for properties (i.e. when calling accessors). Since `lockFocusIfCanDraw` is not an accessor method, you should use the regular square brackets syntax, i.e. `flag = [aView lockFocusIfCanDraw];` instead. | flag = [aView lockFocusIfCanDraw]; |
9,855,673 | It's an interesting problem, really, for all you Devise masters you there.
We have Devise setup with OmniAuth, but the issue happens regardless if you are logged in via Facebook, or logged in via a normal username. What happens is we have a Flash game embedded on our website. When you finish playing the game, the game will submit your score to the Rails backend:
```
request = new URLRequest("http://mydomain.com:2012/games/1/leaderboards/13/submitLeaderboardStatistic");
request.method = URLRequestMethod.POST;
var loader : URLLoader = new URLLoader();
loader.dataFormat = URLLoaderDataFormat.VARIABLES;
var variables : URLVariables = new URLVariables();
variables.game_value = aScore;
variables.game_id = 1;
variables.unique_identifier = "com.onecoolgameaday.highscores";
variables.time_stamp = new Date();
request.data = variables;
loader.addEventListener(Event.COMPLETE, on_complete);
loader.addEventListener(IOErrorEvent.IO_ERROR, onIOError);
loader.load(request);
```
The URL is sent out to our URL. The Controller (Leaderboards are nested underneath Games) gets the url information in the submitLeaderboardStatistic method. This method deals with the information. In this method, I call `current_user` to get the current User, the one who submitted the actual score. Problem is, current\_user returns nil.
Apparently, what is happening, is once the game Launches that URL POST request, devise invalidates the session (or something), so I cannot tell who submitted the score.
Why is the current signed in user being "kicked off" once the Flash Game send the URL? How do I fix this so I can say "user XXX submitted this score."
Thank you!
Rails: 3.2.2
Ruby: 1.9.2
Devise: 1.5.3 | 2012/03/24 | [
"https://Stackoverflow.com/questions/9855673",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/200567/"
] | Does the form you are submitting have a valid CSRF token? I think Devise calls reset\_session if the csrf token is invalid or doesn't exist. | Try to set full URL address to the "/games/1/leaderboards/13/submitLeaderboardStatistic". Probably reason is cross-domail-policy, which should be received from the server, when you using POST method to the different domain. |
21,494,338 | I have some images in my Photo Album. I have already retrieved the asset urls of all of them.. I want to get a particular image using the asset url... below code gave me asset url..
```
ALAssetRepresentation *defaultRepresentation = [asset defaultRepresentation];
NSString *uti = [defaultRepresentation UTI];
NSURL *URL = [[asset valueForProperty:ALAssetPropertyURLs] valueForKey:uti];
```
Now using this url, how can I get the image(UIImage)? | 2014/02/01 | [
"https://Stackoverflow.com/questions/21494338",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/1394304/"
] | Get Url by this,
```
NSURL *url= (NSURL*) [[asset valueForProperty:ALAssetPropertyURLs] valueForKey:[[[asset valueForProperty:ALAssetPropertyURLs] allKeys] objectAtIndex:0]];
```
And get image from url like below.
```
ALAssetsLibraryAssetForURLResultBlock resultblock = ^(ALAsset *myasset)
{
ALAssetRepresentation *rep = [myasset defaultRepresentation];
@autoreleasepool {
CGImageRef iref = [rep fullScreenImage];
if (iref) {
UIImage *image = [UIImage imageWithCGImage:iref];
self.loadedImage = image;
dispatch_async(dispatch_get_main_queue(), ^{
//UIMethod trigger...
});
iref = nil;
}
}
};
ALAssetsLibraryAccessFailureBlock failureblock = ^(NSError *myerror)
{
NSLog(@"Can't get image - %@",[myerror localizedDescription]);
};
ALAssetsLibrary* assetslibrary = [[ALAssetsLibrary alloc] init];
[assetslibrary assetForURL:yourUrl
resultBlock:resultblock
failureBlock:failureblock];
``` | ```
UIImage *img = [UIImage imageWithCGImage:[[myAsset defaultRepresentation] fullResolutionImage]
```
Hope this helps |
994,426 | I know it's not *exactly* what SU is about, but I didn't know where else to turn at this point. I'm trying to hook up a Samsung LA32S81B television to my/a computer using HDMI. This is a moderately old TV, 2007 era, non-smart.
Originally, I tried to hook it up to my laptop, to no avail. I'll save you the long story of all the bug hunting I did, but eventually I came to the discovery that it's not the computer(s) at fault, nor the cable: the TV itself is not recognizing any HDMI from either my laptop or my desktop. My laptop, running win10, and later Win8.1 (after reading in some places win10 and HDMI have known to not play nice) was unable to get a link to the TV, and my desktop is also not able to output to it, or even recognize a screen is connected. Oddly enough, if I hook up, say, a cable box, to the same HDMI ports on the TV, using the same cable, I do get output, and if I for instance use the same HDMI cable and plug it into one of my computer monitors, the computer picks it up fine. It's literally only PC to TV that will NOT work. I've tried onboard graphics, I've tried my GTX970, I've tried old drivers, new drivers, I've factory resetted the TV, it won't budge. Nothing is working. I've tried literally everything I can think of. The only thing I can imagine is happening is that maybe the PCs are all outputting some format the TV won't recognize (which already seems unlikely, especially through HDMI), but then at least I would still imagine my computer to at least *notice* a screen is connected.
Is there *anyone* who has *any* idea what the hell is going on?
further info: desktop is Win10 and is also running two other monitors off of the GTX970, both are connected through DVI. Laptop had Intel onboard graphics, | 2015/10/31 | [
"https://superuser.com/questions/994426",
"https://superuser.com",
"https://superuser.com/users/246510/"
] | In looking at the specs for that TV, it does not support 1080p. Likely, your PC is outputting a 1080p signal and the TV can't sync to it.
Try these things:
* Lower your display resolution to 1280x720 (that's the HDTV 720p spec).
* On the TV, make sure the HDMI input says PC as the source type (Samsungs in particular have undocumented behavior where they overscan/underscan an image depending on what the input type is set to).
* Most laptops have an `Fn`+ key combination to enable/disable/mirror an external display. Fiddle with that to see if it makes a difference.
* In Windows, make sure it understands that you have two screens, and that the "Extend my desktop onto this monitor" checkbox is selected for the TV.
Hope it helps. | I got so sick of this I just bought a new TV |
24,668,826 | Im new to ASP. can any body give the sample code for select all the checkbox while selecting one checkbox from the check box list.
Select All
A
B
C
once checking the select all check from the checkbox list all other items also should get selected. | 2014/07/10 | [
"https://Stackoverflow.com/questions/24668826",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/3823967/"
] | From you image it seems like you presented the ViewController using push
The `dismissViewControllerAnimated` is used to close ViewControllers that presented using modal
**Swift 2**
```
navigationController.popViewControllerAnimated(true)
```
**Swift 4**
```
navigationController?.popViewController(animated: true)
dismiss(animated: true, completion: nil)
``` | **In Swift 3.0**
If you want to dismiss a presented view controller
```
self.dismiss(animated: true, completion: nil)
``` |
24,668,826 | Im new to ASP. can any body give the sample code for select all the checkbox while selecting one checkbox from the check box list.
Select All
A
B
C
once checking the select all check from the checkbox list all other items also should get selected. | 2014/07/10 | [
"https://Stackoverflow.com/questions/24668826",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/3823967/"
] | From you image it seems like you presented the ViewController using push
The `dismissViewControllerAnimated` is used to close ViewControllers that presented using modal
**Swift 2**
```
navigationController.popViewControllerAnimated(true)
```
**Swift 4**
```
navigationController?.popViewController(animated: true)
dismiss(animated: true, completion: nil)
``` | If you are presenting a ViewController modally, and want to go back to the root ViewController, take care to dismiss this modally presented ViewController before you go back to the root ViewController otherwise this ViewController will not be removed from Memory and cause Memory leaks. |
24,668,826 | Im new to ASP. can any body give the sample code for select all the checkbox while selecting one checkbox from the check box list.
Select All
A
B
C
once checking the select all check from the checkbox list all other items also should get selected. | 2014/07/10 | [
"https://Stackoverflow.com/questions/24668826",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/3823967/"
] | I have a solution for your problem. Please try this code to dismiss the view controller if you present the view using modal:
Swift 3:
```
self.dismiss(animated: true, completion: nil)
```
OR
If you present the view using "push" segue
```
self.navigationController?.popViewController(animated: true)
``` | **In Swift 3.0**
If you want to dismiss a presented view controller
```
self.dismiss(animated: true, completion: nil)
``` |
24,668,826 | Im new to ASP. can any body give the sample code for select all the checkbox while selecting one checkbox from the check box list.
Select All
A
B
C
once checking the select all check from the checkbox list all other items also should get selected. | 2014/07/10 | [
"https://Stackoverflow.com/questions/24668826",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/3823967/"
] | From Apple [documentations](https://developer.apple.com/documentation/uikit/uiviewcontroller/1621505-dismiss):
>
> The presenting view controller is responsible for dismissing the view controller it presented
>
>
>
Thus, it is a bad practise to just invoke the [dismiss](https://developer.apple.com/documentation/uikit/uiviewcontroller/1621505-dismiss) method from it self.
What you should do if you're presenting it modal is:
```
presentingViewController?.dismiss(animated: true, completion: nil)
``` | Since you used push presented viewController, therefore, you can use
```
self.dismiss(animated: false, completion: nil)
``` |
24,668,826 | Im new to ASP. can any body give the sample code for select all the checkbox while selecting one checkbox from the check box list.
Select All
A
B
C
once checking the select all check from the checkbox list all other items also should get selected. | 2014/07/10 | [
"https://Stackoverflow.com/questions/24668826",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/3823967/"
] | Use:
```
self.dismiss(animated: true, completion: nil)
```
instead of:
```
self.navigationController.dismissViewControllerAnimated(true, completion: nil)
``` | Try this:
```
@IBAction func close() {
dismiss(animated: true, completion: nil)
}
``` |
24,668,826 | Im new to ASP. can any body give the sample code for select all the checkbox while selecting one checkbox from the check box list.
Select All
A
B
C
once checking the select all check from the checkbox list all other items also should get selected. | 2014/07/10 | [
"https://Stackoverflow.com/questions/24668826",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/3823967/"
] | In Swift 3.0 to 4.0 it's as easy as typing this into your function:
```
self.dismiss(animated: true, completion: nil)
```
Or if you're in a navigation controller you can "pop" it:
```
self.navigationController?.popViewController(animated: true)
``` | If you using the present method in the parent VC then you should call this function, to dismiss the child VC use this
```
self.dismiss(animated: true, completion: nil)
```
if you calling child VC by using push method, to dismiss the child VC use this
```
self.navigationController?.popViewController(animated: true)
``` |
24,668,826 | Im new to ASP. can any body give the sample code for select all the checkbox while selecting one checkbox from the check box list.
Select All
A
B
C
once checking the select all check from the checkbox list all other items also should get selected. | 2014/07/10 | [
"https://Stackoverflow.com/questions/24668826",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/3823967/"
] | I have a solution for your problem. Please try this code to dismiss the view controller if you present the view using modal:
Swift 3:
```
self.dismiss(animated: true, completion: nil)
```
OR
If you present the view using "push" segue
```
self.navigationController?.popViewController(animated: true)
``` | In Swift 3.0 to 4.0 it's as easy as typing this into your function:
```
self.dismiss(animated: true, completion: nil)
```
Or if you're in a navigation controller you can "pop" it:
```
self.navigationController?.popViewController(animated: true)
``` |
24,668,826 | Im new to ASP. can any body give the sample code for select all the checkbox while selecting one checkbox from the check box list.
Select All
A
B
C
once checking the select all check from the checkbox list all other items also should get selected. | 2014/07/10 | [
"https://Stackoverflow.com/questions/24668826",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/3823967/"
] | Use:
```
self.dismiss(animated: true, completion: nil)
```
instead of:
```
self.navigationController.dismissViewControllerAnimated(true, completion: nil)
``` | Since you used push presented viewController, therefore, you can use
```
self.dismiss(animated: false, completion: nil)
``` |
24,668,826 | Im new to ASP. can any body give the sample code for select all the checkbox while selecting one checkbox from the check box list.
Select All
A
B
C
once checking the select all check from the checkbox list all other items also should get selected. | 2014/07/10 | [
"https://Stackoverflow.com/questions/24668826",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/3823967/"
] | I have a solution for your problem. Please try this code to dismiss the view controller if you present the view using modal:
Swift 3:
```
self.dismiss(animated: true, completion: nil)
```
OR
If you present the view using "push" segue
```
self.navigationController?.popViewController(animated: true)
``` | If you are presenting a ViewController modally, and want to go back to the root ViewController, take care to dismiss this modally presented ViewController before you go back to the root ViewController otherwise this ViewController will not be removed from Memory and cause Memory leaks. |
24,668,826 | Im new to ASP. can any body give the sample code for select all the checkbox while selecting one checkbox from the check box list.
Select All
A
B
C
once checking the select all check from the checkbox list all other items also should get selected. | 2014/07/10 | [
"https://Stackoverflow.com/questions/24668826",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/3823967/"
] | From you image it seems like you presented the ViewController using push
The `dismissViewControllerAnimated` is used to close ViewControllers that presented using modal
**Swift 2**
```
navigationController.popViewControllerAnimated(true)
```
**Swift 4**
```
navigationController?.popViewController(animated: true)
dismiss(animated: true, completion: nil)
``` | If you presenting a controller without a Navigation Controller, you can call the following code from a method of the presented controller.
```
self.presentingViewController?.dismiss(animated: true, completion: nil)
```
If your ViewController is presented modally, optional presentingViewController will be not nil and the code will be executed. |
57,012,262 | i want to use the optional arguments without `-` or `--`,
want to achive something like this:
```
scriptname install <other options>
scriptname uninstall <other options>
```
my code:
```
parser = argparse.ArgumentParser()
parser.add_argument("install","INSTALL",action='store_true',help="INSTALL SOMETHING",default="")
parser.add_argument("uninstall","UNINSTALL",action='store_true',help="UNINSTALL SOMETHING",default="")
args = parser.parse_args()
if args.install:
install logic
if args.uninstall:
uninstall logic
```
getting the error below
```
ValueError: invalid option string 'install': must start with a character '-'
``` | 2019/07/12 | [
"https://Stackoverflow.com/questions/57012262",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/8369163/"
] | You don't have to use Selenium when you can just extract the match stats right off the HTML:
```py
import re
from ast import literal_eval
url = 'https://www.whoscored.com/Matches/1294545/LiveStatistics/Germany-Bundesliga-2018-2019-Bayern-Munich-Hoffenheim'
res = requests.get(
url,
headers={
'user-agent': 'Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:69.0) Gecko/20100101 Firefox/69.0',
}
)
res.raise_for_status()
html = res.text
```
so far nothing special.
```py
match_data = re.search('var matchStats = ([^;]+)', html, flags=re.MULTILINE).group(1)
match_data_clean = re.sub(',,', ",'',", match_data_clean)
stats = literal_eval(match_data_clean)
```
when we inspect `match_data` we can see a bunch of arrays with invalid syntax, like this:
```
ams',,'yellow',,,21,328
```
so we clean that off with a bit of `re` magic by inserting empty strings between commas.
Printing `stats` gives us:
```
[[[37,
1211,
'Bayern Munich',
'Hoffenheim',
'24/08/2018 19:30:00',
'24/08/2018 00:00:00',
6,
'FT',
'1 : 0',
'3 : 1',
'',
'',
'3 : 1',
'Germany',
'Germany'],
[[[21, [], [['Kasim Adams', '', 'yellow', '', '', 21, 328428, 0]], 0, 1],
[23,
[['Thomas Müller',
'Joshua Kimmich',
'goal',
'(1-0)',
'',
23,
37099,
283323]],
[],
1,
0],
```
from here on, it's just finding the right indices that correspond to the data you're looking for. | Request is not the best tool to parse data in this case because this website uses JavaScript, so it is better to use Selenium and a web driver.
I gave it a try and I could parse the names of the players of both teams in 2 different lists.
```
from selenium import webdriver
from bs4 import BeautifulSoup
from selenium.webdriver.common.by import By
from selenium.webdriver.support.ui import WebDriverWait
from selenium.webdriver.support import expected_conditions as ec
import time
# Open web page
driver = webdriver.Firefox(executable_path='YOUR PATH') #You have to put the path of your WebDriver
driver.get('https://www.whoscored.com/Matches/1294545/LiveStatistics/Germany-Bundesliga-2018-2019-Bayern-Munich-Hoffenheim')
# Accept
element=WebDriverWait(driver,20).until(ec.element_to_be_clickable((By.XPATH,"/html/body/div[1]/div/div/div[2]/button")))
driver.execute_script("arguments[0].click();", element)
time.sleep(3)
# Scrolling down the page
results = driver.find_element_by_css_selector("#statistics-table-home-summary > table:nth-child(1)")
driver.execute_script("arguments[0].scrollIntoView();", results)
time.sleep(7)
# Make soup
source = driver.page_source
soup = BeautifulSoup(source, 'lxml')
table_home = soup.find_all('table', {"id": "top-player-stats-summary-grid"})[0]
players_home = [a.text for a in table_home.find_all('a')]
print(players_home)
table_away = soup.find_all('table', {"id": "top-player-stats-summary-grid"})[1]
players_away = [a.text for a in table_away.find_all('a')]
print(players_away)
driver.quit()
``` |
2,773,644 | I'd like to host a WCF web service in IIS. The service should keep a certain set of data all the time, it must never be lost.
My colleague told me this is impossible because IIS closes down the service after a certain time (I assume without any activity). Is that true? How do I prevent that behavior?
In case it matters, both IIS 6 and 7 are available. | 2010/05/05 | [
"https://Stackoverflow.com/questions/2773644",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/39590/"
] | By default, IIS recycles the worker process after a certain period of inactivity (20 mins if I recall correct). This causes your data to be lost.
You can turn off this behavior in the Properties page of the ApplicationPool under which your app is running.
EDIT: having said that, if it is *really* important that this data is never lost, I would consider storing it in a database or some other form of storage. | >
> My colleague told me this is
> impossible because IIS closes down the
> service after a certain time (I assume
> without any activity). Is that true?
> How do I prevent that behavior?
>
>
>
This is true, but you can get around it by using an out of process state server.
Here are three links describing session state and how to set it up in IIS:
<http://www.microsoft.com/technet/prodtechnol/WindowsServer2003/Library/IIS/0d9dc063-dc1a-46be-8e84-f05dbb402221.mspx?mfr=true>
<http://www.eggheadcafe.com/articles/20021016.asp>
<http://msdn.microsoft.com/en-us/library/ms178586.aspx> |
74,360,884 | I deleted a category which is an f-key of the items table. Now the view has an error saying 'Attempt to read property "category\_name" on null'. How do I render a null foreign key?
I tried if-else:
```
@if({{$item->category->category_name}} === 'null')
<h2>no category</h2>
@else
{{ $item->category->category_name}}
@endif
``` | 2022/11/08 | [
"https://Stackoverflow.com/questions/74360884",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/17040377/"
] | Try this:
```
@if ($item->category)
{{ $item->category->category_name }}
@else
<h2>no category</h2>
@endif
```
Or simply
```
<h2>{{ $item->category?->category_name ?? 'no category' }}</h2>
``` | In PHP8 or Larvel 8
simple use this one
```
<h2>{{ $item->category->category_name ? 'no category' }}</h2>
``` |
53,301,678 | I am using post navigation for my blog. For this portion i wrote some css. It's working fine. But the problem is for the very latest post , it's showing blank space for next post link. Same thing is happened with oldest post, it's showing again bank space for previous post link. [](https://i.stack.imgur.com/SFMaK.png)
I add code snippet for this portion. Can i anyone suggest how can i modify my css for this portion. Following code is embedded in php file.
```
<div class="row justify-content-center">
<div class="sewl-more-posts">
<div class="previous-post">
<?php If(previous_post_link()){?>
<span class="post-control-link">Previous Article</span>
<span class="post-name"><?php previous_post_link(); ?></span>
<?php } ?>
</div>
<div class="next-post">
<?php If(next_post_link()){?>
<span class="post-control-link">Next Article</span>
<span class="post-name"><?php next_post_link(); ?></span>
<?php } ?>
</div>
</div>
</div>
``` | 2018/11/14 | [
"https://Stackoverflow.com/questions/53301678",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/10043462/"
] | First, output the divs only if they'll have content:
```
<div class="sewl-more-posts">
<?php if (previous_post_link()){?>
<div class="previous-post">
<span class="post-control-link">Previous Article</span>
<span class="post-name"><?php previous_post_link(); ?></span>
</div>
<?php } ?>
<?php if (next_post_link()){?>
<div class="next-post">
<span class="post-control-link">Next Article</span>
<span class="post-name"><?php next_post_link(); ?></span>
</div>
<?php } ?>
</div>
```
This way, if the previous-post or next-post div is missing, you'll be able to target the remaining one with the [`:only-child` pseudo class](https://developer.mozilla.org/en-US/docs/Web/CSS/:only-child):
```
.sewl-more-posts > div:only-child {
text-align: center;
}
``` | You cannot do this with php once the page is generated client-side, therefore you have to use javascript (for example):
```javascript
onclick = documet.getElementById('the id you have').style.property = "blue";
``` |
8,177,473 | ```
int array[10] = {1,2,3,4,5,6,7,8};
int *ptr = array;
std::cout<<*(ptr+ 2); => O/P = 3
int (*arr_ptr)[10] = &array;
std::cout<<*(*arr_ptr+2); => O/P = 3
```
Whats the difference between these 2. I know what they mean, but if they give same result why do we have 2 different notations? | 2011/11/18 | [
"https://Stackoverflow.com/questions/8177473",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/996330/"
] | The first case is the normal case: `ptr` is a pointer to the first element of the array `array`, and it is indexed (using `*(ptr+2)`, which is a synonym for `ptr[2]`) to access the third element of that array.
The second case is contrived: `arr_ptr` is a pointer to the (enitre) array `array`. It is first dereferenced (with `*arr_ptr`) to yield the array itself, which is then used as an argument to binary `+`, which causes it to get implicitly converted to a (nameless) pointer to its first element, which is then indexed in the same way `*(<nameless pointer>+2)` and gives the same result.
Making those implicit conversions explicit, you could write
```
int *ptr = &array[0];
std::cout<<*(ptr+ 2);
int (*arr_ptr)[10] = &array;
std::cout<<*( &(*arr_ptr)[0] + 2 );
``` | Use the notation that you understand and that fits the problem domain. If your app has an array, then use array notation. If you have to push pointers around for some other reason, then the second version is appropriate. |
8,177,473 | ```
int array[10] = {1,2,3,4,5,6,7,8};
int *ptr = array;
std::cout<<*(ptr+ 2); => O/P = 3
int (*arr_ptr)[10] = &array;
std::cout<<*(*arr_ptr+2); => O/P = 3
```
Whats the difference between these 2. I know what they mean, but if they give same result why do we have 2 different notations? | 2011/11/18 | [
"https://Stackoverflow.com/questions/8177473",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/996330/"
] | The first case is the normal case: `ptr` is a pointer to the first element of the array `array`, and it is indexed (using `*(ptr+2)`, which is a synonym for `ptr[2]`) to access the third element of that array.
The second case is contrived: `arr_ptr` is a pointer to the (enitre) array `array`. It is first dereferenced (with `*arr_ptr`) to yield the array itself, which is then used as an argument to binary `+`, which causes it to get implicitly converted to a (nameless) pointer to its first element, which is then indexed in the same way `*(<nameless pointer>+2)` and gives the same result.
Making those implicit conversions explicit, you could write
```
int *ptr = &array[0];
std::cout<<*(ptr+ 2);
int (*arr_ptr)[10] = &array;
std::cout<<*( &(*arr_ptr)[0] + 2 );
``` | After editing your question, following are the differences:
```
(1) int *ptr = array;
```
`array` gets decayed to the pointer. `ptr` is ideally allowed to point to any `int[]` irrespective of its size
```
(2) int (*arr_ptr)[10] = &array;
```
`arr_ptr` is a pointer to an `int[10]`. It's very specific definition and you can never assign an array to `arr_ptr` which has size other than `10`.
```
int array_2[20];
arr_ptr = &array_2; // error
``` |
8,177,473 | ```
int array[10] = {1,2,3,4,5,6,7,8};
int *ptr = array;
std::cout<<*(ptr+ 2); => O/P = 3
int (*arr_ptr)[10] = &array;
std::cout<<*(*arr_ptr+2); => O/P = 3
```
Whats the difference between these 2. I know what they mean, but if they give same result why do we have 2 different notations? | 2011/11/18 | [
"https://Stackoverflow.com/questions/8177473",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/996330/"
] | The first case is the normal case: `ptr` is a pointer to the first element of the array `array`, and it is indexed (using `*(ptr+2)`, which is a synonym for `ptr[2]`) to access the third element of that array.
The second case is contrived: `arr_ptr` is a pointer to the (enitre) array `array`. It is first dereferenced (with `*arr_ptr`) to yield the array itself, which is then used as an argument to binary `+`, which causes it to get implicitly converted to a (nameless) pointer to its first element, which is then indexed in the same way `*(<nameless pointer>+2)` and gives the same result.
Making those implicit conversions explicit, you could write
```
int *ptr = &array[0];
std::cout<<*(ptr+ 2);
int (*arr_ptr)[10] = &array;
std::cout<<*( &(*arr_ptr)[0] + 2 );
``` | They are not in fact the same to the compiler, and will result in different assembly language being generated.
Here is some good reference on the difference: <http://cplusplus.com/forum/articles/10/> |
8,177,473 | ```
int array[10] = {1,2,3,4,5,6,7,8};
int *ptr = array;
std::cout<<*(ptr+ 2); => O/P = 3
int (*arr_ptr)[10] = &array;
std::cout<<*(*arr_ptr+2); => O/P = 3
```
Whats the difference between these 2. I know what they mean, but if they give same result why do we have 2 different notations? | 2011/11/18 | [
"https://Stackoverflow.com/questions/8177473",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/996330/"
] | After editing your question, following are the differences:
```
(1) int *ptr = array;
```
`array` gets decayed to the pointer. `ptr` is ideally allowed to point to any `int[]` irrespective of its size
```
(2) int (*arr_ptr)[10] = &array;
```
`arr_ptr` is a pointer to an `int[10]`. It's very specific definition and you can never assign an array to `arr_ptr` which has size other than `10`.
```
int array_2[20];
arr_ptr = &array_2; // error
``` | Use the notation that you understand and that fits the problem domain. If your app has an array, then use array notation. If you have to push pointers around for some other reason, then the second version is appropriate. |
8,177,473 | ```
int array[10] = {1,2,3,4,5,6,7,8};
int *ptr = array;
std::cout<<*(ptr+ 2); => O/P = 3
int (*arr_ptr)[10] = &array;
std::cout<<*(*arr_ptr+2); => O/P = 3
```
Whats the difference between these 2. I know what they mean, but if they give same result why do we have 2 different notations? | 2011/11/18 | [
"https://Stackoverflow.com/questions/8177473",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/996330/"
] | After editing your question, following are the differences:
```
(1) int *ptr = array;
```
`array` gets decayed to the pointer. `ptr` is ideally allowed to point to any `int[]` irrespective of its size
```
(2) int (*arr_ptr)[10] = &array;
```
`arr_ptr` is a pointer to an `int[10]`. It's very specific definition and you can never assign an array to `arr_ptr` which has size other than `10`.
```
int array_2[20];
arr_ptr = &array_2; // error
``` | They are not in fact the same to the compiler, and will result in different assembly language being generated.
Here is some good reference on the difference: <http://cplusplus.com/forum/articles/10/> |
3,763,347 | I am trying to figure out the Taylor coefficient of $\exp\left\{\frac{z+1}{z-1}\right\}$. My idea is as follows:
$$f(z)=\exp\left\{\frac{z+1}{z-1}\right\}=\exp\left\{1+\frac{2}{z-1}\right\}=e\exp\left\{\frac{2}{z-1}\right\}.$$
Then we have $f(z)=e\sum\_{n=0}^{+\infty}\frac{w^n}{n!}$, where $w=\frac{2}{z-1}$. Clearly, we have
$$w^n=(-2)^n(1-z)^{-n}=(-2)^n\sum\_{k=0}^{+\infty}\frac{\Gamma(n+k)}{k!\Gamma(n)}z^k.$$
It follows that
$$f(z)=e\sum\_{n=0}^{+\infty}\frac{w^n}{n!}=e\sum\_{n=0}^{+\infty}\frac{(-2)^n}{n!}\sum\_{k=0}^{+\infty}\frac{\Gamma(n+k)}{k!\Gamma(n)}z^k=e\sum\_{k=0}^{+\infty}\sum\_{n=0}^{+\infty}\frac{(-2)^n}{n!}\frac{\Gamma(n+k)}{k!\Gamma(n)}z^k.$$
Namely, the $n$-th coefficient of $f$ is given by
$$\widehat{f}(k)=e\sum\_{n=0}^{+\infty}\frac{(-2)^n}{n!}\frac{\Gamma(n+k)}{k!\Gamma(n)}.$$
I have checked that $\widehat{f}(0)=f(0)$ and $\widehat{f}(1)=f'(0)$. Moreover, the fact that $f''(0)=0$ implies that $\widehat{f}(2)$ should be zero. But in our result it seems that
$$\widehat{f}(2)=e\sum\_{n=0}^{+\infty}\frac{(-2)^n}{n!}\frac{\Gamma(n+2)}{2!\Gamma(n)}\neq 0.$$
What is wrong with my formula? Could you help me figure our the problem and tfind out the Taylor coefficient of the $f$? Thank you! | 2020/07/20 | [
"https://math.stackexchange.com/questions/3763347",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/83239/"
] | Write
$$ f(z):=\exp{\big(\frac{z+1}{z-1}\big)} =\frac{1}{e}\exp{\big(\frac{2z}{z-1}\big)} $$
Use the generating function for the Laguerre polynomials to show
$$ f(z)=\frac{1}{e} \sum\_{n=0}^\infty L\_n^{(-1)}(2)z^n $$
Thus, using the 'coefficient of' operator
$$ [z^n] f(z) = \frac{1}{e} L\_n^{(-1)}(2) .$$
It is perhaps more convenient to look up the explicit construction of the Laguerre polynomial and write this as
$$ [z^n] f(z) = \frac{1}{e}\sum\_{m=0}^n(-1)^m\binom{n-1}{n-m}\frac{2^m}{m!} .$$ | You can easily generate the coefficients $a\_n$ of
$$f(z)=\exp\left(\frac{z+1}{z-1}\right)=\frac 1e\sum\_{n=0}^\infty a\_n \,z^n$$ using the reccurence formula
$$a\_n=\frac{n-2}n\,({2a\_{n-1}-a\_{n-2}}) \quad \text{with} \quad a\_0=1 \quad \text{and} \quad a\_1=- 2 $$ |
Subsets and Splits