import sys                             # system module 
import pandas as pd                    # data package
import matplotlib.pyplot as plt        # graphics module  
import datetime as dt                  # date and time module
import numpy as np                     # foundation for Pandas 

%matplotlib inline                     

# check versions (overkill, but why not?)
print('Python version: ', sys.version)
print('Pandas version: ', pd.__version__)
print('Today: ', dt.date.today())

"""
Explanation: Pandas 4:  Describing data
More Pandas data management tools.  

describe
mean, median, std etc 
value_counts 
groupby (***) 

Apps 

Poll 
Chipotle 
MovieLens (with requests worked in) 

Note: requires internet access to run.  
<!-- 
internal links http://sebastianraschka.com/Articles/2014_ipython_internal_links.html
-->

This IPython notebook was created by Dave Backus, Chase Coleman, and Spencer Lyon for the NYU Stern course Data Bootcamp.  
<a id=prelims></a>
Preliminaries
End of explanation
"""


url = 'https://raw.githubusercontent.com/TheUpshot/chipotle/master/orders.tsv'
chp = pd.read_csv(url, sep='\t')   # tab (\t) delimited 
print('Variable dtypes:\n', chp.dtypes, sep='')
chp.head()

"""
Explanation: <a id=want></a>
The want operator
We need to know what we're trying to do -- what we want the data to look like.  We say we apply the want operator.  
Some problems we've run across that ask to be solved:

Numerical data is contaminated by commas (marking thousands) or dollar signs.  
Row and column labels are contaminated.  
Missing values are marked erratically.  
We have too much data, would prefer to choose a subset.  
Variables run across rows rather than down columns.  

What we want in each case is the opposite of what we have:  we want nicely formatted numbers, clean row and column labels, and so on.  
We'll solve the first four problems here, the last one in the next notebook.  
Example:  Chipotle data
This data comes from a New York Times story
End of explanation
"""


pd.set_option("display.width", 80)

import pandas as pd
url1 = 'http://pages.stern.nyu.edu/~dbackus/Data/'
url2 = 'Data-Bootcamp-entry-poll_s16.csv'
url = url1 + url2 
ep = pd.read_csv(url, header=0) 
print('Dimensions:', ep.shape)
print('\nData types:\n', ep.dtypes, sep='')
ep.head(2) 

"""
Explanation: Comment. Note that the variable item_price has dtype object. The reason is evidently the dollar sign.  We'd prefer to have it as a number, specifically a float.  
Example:  Data Bootcamp entry poll
This is the poll we did at the start of the course.  Responses were collected in a Google spreadsheet, which we converted to a csv and uploaded to our website.
End of explanation
"""


# rename variables 
newnames = ['time', 'program', 'career', 'programming', 'stats', 'media',
             'other', 'major', 'data', 'why', 'topics']
newnames = [name.title() for name in newnames]             
ep.columns = newnames  
ep.head()

# check multi-response question to see what we're dealing with 
ep['Media'].head(20)

"""
Explanation: Comments. This is mostly text data, which means it's assigned the dtype object.  Which is fine.  But there are two things that would make the data easier to work with:

The column names are excessively verbose.  This one's easy:  We replace them with single words.  Which we do below.  
The second one is harder.  Two of the questions -- social media and special topics -- say "mark all that apply."  In the spreadsheet, we have a list of every choice the person checked.  Our want is to count the number of each type of response.  For example, we might want a bar chart that gives us the number of each response.  The question is how we get there.
End of explanation
"""


url1 = 'http://www.oecd.org/health/health-systems/'
url2 = 'OECD-Health-Statistics-2015-Frequently-Requested-Data.xls'
docs = pd.read_excel(url1+url2, 
                     skiprows=3, 
                     usecols=[0, 51, 52, 53, 54, 55, 57],
                     sheetname='Physicians', 
#                     na_values=['..'],
                     skip_footer=21) 
print('Dimensions:', docs.shape)
print('\nIndex', docs.index.tolist(), sep='')
print('\nVariable dtypes:\n', docs.dtypes.tail(8), sep='')
docs.head()

"""
Explanation: Comment.  Note the commas separating answers with more than one choice.  We want to unpack them somehow.  
Example:  OECD healthcare statistics
The OECD collects healthcare data on lots of (mostly rich) countries, which is helpful in producing comparisons.  Here we use a spreadsheet linked in one of their documents.
End of explanation
"""


names = list(docs)
docs = docs.rename(columns={names[0]: 'Country'})
docs.head(2)

"""
Explanation: Comments.  Here we have a couple issues.  

The first column includes a space and a number:  Australia 1, Chile 3, etc.  We care about this because when we plot the data across countries, the country labels are going to be country names, so we want them in a better form than this.  
The ..'s in the sheet lead us to label any column that includes them as dtype object.  Here we want to label them as missing values.  
If we want to plot each country against time, then we'll need to switch the rows and columns somehow, so that the x axis in the plot (the year) is the index and not the column label.  

One more thing before we proceeed:  change the name of the country variable.
End of explanation
"""


url1 = 'http://www.imf.org/external/pubs/ft/weo/2015/02/weodata/'
url2 = 'WEOOct2015all.xls'
url = url1 + url2 
weo = pd.read_csv(url, sep='\t', 
                  usecols=[1,2,3,4,6,40,41,42,43,44], 
                  thousands=',', 
                  na_values=['n/a', '--']
                 )

print('Variable dtypes:\n', weo.dtypes, sep='')
weo.head()

"""
Explanation: Example:  World Economic Outlook
The IMF's World Economic Outlook database contains a broad range of macroeconomic data for a large number of countries.  It's updated twice a year and is a go-to source for things like current account balances (roughly, the trade balance) and government debt and deficits.  It also has a few quirks, as we'll see.  
Example. Run the following code as is, and with the thousands and na_values parameters commented out.  How do the dtypes differ?
End of explanation
"""


weo.T.head(10)

"""
Explanation: Comment. This has several issues:  

The variables run across rows with observations labeled 1980, 1981, etc across the top.  We saw the same problem in the previous example.    
If we run the first version of the read_csv statement, the data columns (1980, 1981, etc) have dtype object.  A little work suggests that this is because they include commas marking thousands.   
The entries labeled n/a need to be marked as missing values.

We can solve the last two in the read_csv function by deleting the hash -- which is what we see in the second read_csv statement.  The other one takes some work.  
Question.  Can we transpose the whole thing to get the data running down columns?
End of explanation
"""


dollars = '$123.45'
print('Type of variable dollars:', type(dollars))
num = dollars.replace('$', '')
num = float(num)
print('Type of variable num:', type(num))

"""
Explanation: <a id='strings'></a>
String methods
We can treat variables as strings in Pandas in much the same way we dealt with strings in core Python.  Run the code below to remind yourself how this works.
End of explanation
"""


chp.head()

chpnum = chp.copy()
print('Original dtype:', chpnum['item_price'].dtype)
# create a copy of the df to play with 

# delete dollar signs
chpnum['item_price'].str.replace('$', '').head()

# delete dollar signs, convert to float, and assign back to chpnum 
chpnum['item_price'] = chpnum['item_price'].str.replace('$', '').astype(float)
print('New dtype:', chpnum['item_price'].dtype)

# assign back to chp for future use 
chp = chpnum

"""
Explanation: Pandas string methods. We can do the same thing to all the observations of a variable with so-called string methods.  We append .str to a variable in a dataframe and then apply the string method of our choice.  If this is part of converting a number-like entry that has mistakenly been given dtype object, we then convert its dtype with the astype method.  
Example.  Let's use a string method to fix the item_price variable in the Chipotle dataframe.  This has three parts: 

Use the method str to identify this as a string method.
Apply the string method of our choice (here replace) to fix the string.
Use the astype method to convert the fixed-up string to a float. 

We start by making a copy of the chp dataframe that we can experiment with.
End of explanation
"""


# try this with an example first 
country = 'United States 1'

# get documentation for the rsplit method
#country.rsplit?

# an example 
country.rsplit()

"""
Explanation: Comment. We did everything here in one line:  replace the dollar sign with a string method, then converted to float using astype.  If you think this is too dense, you might break it into two steps.  
Example. Here we strip off the numbers at the end of the indexes in the OECD docs dataframe.  This involves some experimentation:  

Play with the rsplit method to see how it works.  
Apply rsplit to the example country = 'United States 1'.  
Use a string method to do this to all the entries of the variable Country.
End of explanation
"""


# what about this?
country.rsplit(maxsplit=1)

# one more step, we want the first component of the list
country.rsplit(maxsplit=1)[0]

docs["Country"].head()

# now do this for the variable Country 
#docs['Country'].str.rsplit(maxsplit=1).str[0].head()   # explain why this doesn't work 
docs['Country'].str.rsplit(n=1).str[0].head() 

# some people prefer the get method to slicing 
docs['Country'].str.rsplit(n=1).str.get(0).head()

# now assign it to newdocs and see what we have 
newdocs = docs.copy()
newdocs['Country'] = newdocs['Country'].str.rsplit(n=1).str.get(0)
newdocs.head()

# assign it back to docs for future use 
docs = newdocs 

"""
Explanation: Comment. Not quite, we only want to split once.
End of explanation
"""


docs = newdocs
docs.head()

"""
Explanation: Comments. 

Note that we need two str's here:  one to do the split, the other to extract the first element.  
For reasons that mystify us, we ran into problems when we used maxsplit=1, but it works with n=1. 
This is probably more than you want to know, but file away the possibilities in case you need them.  

<a id='missing'></a>
Missing values
It's important to label missing values, so that Pandas doesn't interpret entries as strings.  Pandas is also smart enough to ignore things labeled missing when it does calculations or graphs.  If we compute, for example, the mean of a variable, the default is to ignore missing values.  
We've seen that we can label certain entries as missing values in read statements:  read_csv, read_excel, and so on.  Here we do it directly, mostly to remind ourselves what's involved.  
Marking missing values
Example. The docs dataframe contains a number of instances of .. (double period).  How can we mark them as missing values?
End of explanation
"""


docs.replace(to_replace=['..'], value=[None]).head()

"""
Explanation: What to do.  We use the replace method on the whole dataframe.  To mark something as missing, we replace it as None, which Pandas interprets as missing and labels NaN.
End of explanation
"""


docs.dtypes.head()

docsna = docs.replace(to_replace=['..'], value=[None])
docsna.dtypes.head()

"""
Explanation: Comment.  Replace automatically updates the dtypes.  Here the double dots led us to label the variables as objects.  After the replace, they're now floats, as they should be.
End of explanation
"""


docs.replace(to_replace=['..'], value=[np.nan]).head()

# assign back to docs 
docs = docs.replace(to_replace=['..'], value=[np.nan])

"""
Explanation: Comment.  Some people prefer to use the numpy nan.  Here's an example.  The only advantage is that we avoid possible conflicts with other uses of the value None.
End of explanation
"""


docs.replace(to_replace=['.'], value=['*']).head()

"""
Explanation: Comment. Unlike the string methods we described earlier, this use of replace affects complete entries, not elements of string entries.  For example, suppose we tried to replace the periods in decimal numbers with an asterisk.  We could try the following, but it doesn't work:  the decimal numbers  don't change.
End of explanation
"""


# grab a variable to play with
var = docsna[2013].head(10)
var

# which ones are missing ("null")?
var.isnull()

# which ones are not missing ("not null")?
var.notnull()

# drop the missing 
var.dropna()

"""
Explanation: Working with missing values
End of explanation
"""


docs[2013].plot.barh(figsize=(4, 12)) 

"""
Explanation: Comment. We usually don't have to worry about this, Pandas takes care of missing values automatically.  
Comment. Let's try a picture to give us a feeling of accomplishment. What else would you say we need?  How would we get it?
End of explanation
"""


# we create a small dataframe to experiment with 
small = weo.head()
small

"""
Explanation: <a id='selection'></a>
Selecting variables and observations
The word selection refers to choosing a subset of variables or observations using their labels or index.  Similar methods are sometimes referred to as slicing, subsetting, indexing, or filtering.  We'll treat the terms as synonymous.  
There are lots of ways to do this.  Mostly we do "Boolean" selection, which we address in the next section.  We review more direct options here, mostly at high speed because they're not things we use much.  
In the outline below, df is a dataframe, var and varn are variable names, vlist = ['var1', 'var2'] is a list of variable names, and nlist = [0, 3, 4] is a list of numerical variable or observation indexes, and n1 and n2 are integers.  Some of the basic selection/indexing/slicing methods have the form:  

df[var] extracts a variable -- a series, in other words.
df[var][3] extracts observation 3 (starting at zero) from the series df[var]. 
df[vlist] extracts a new dataframe consisting of the variables in vlist.  
df[nlist] does the same thing.  
df[n1:n2] extracts observations n1 to n2-1, the traditional slicing syntax.  

We find the last one confusing:  it extracts rows, not columns.  Pandas guru Wes McKinney notes: "This might seem inconsistent to some readers."  Yup!  We don't do it much, partly for that reason.  
<!-- page 127 top -->

The Pandas docs push the loc and iloc methods.  We'll ignore them -- we don't use them much -- but if you're interested, see the docs.
End of explanation
"""


weo.head()

"""
Explanation: Exercise. Try each of these in a different cell and explain what they do:  

small[['ISO', 'Units']]
small[[0, 4]]
small['2011']
small['2011'][3]
small[1:3]

<a id='boolean'></a>
<a id='boolean'></a>
Boolean selection
This is mostly what we do:  we choose observations that satisfy one or more conditions.  We work through this one step at a time:  

Example:  apply the want operator  
Comparisons for dataframes 
Boolean selection:  select observations for which the comparison is True
The isin method

This is easier to describe with an example.  
Example:  Apply the want operator to WEO
Our want here is to take the weo dataframe and extract government debt and deficits for a given set of countries.  Putting this to work involves several steps.  
Here's the head of the dataframe to give us a sense of what we're dealing with.
End of explanation
"""


variable_list = weo[['WEO Subject Code', 'Subject Descriptor', 'Units']].drop_duplicates()
print('Number of variables: ', variable_list.shape[0])
variable_list.head()

country_list = weo[['ISO', 'Country']].drop_duplicates()
print('Number of countries: ', country_list.shape[0])
country_list.head()

"""
Explanation: Find variable and country codes. Which ones do we want?  Let's start by seeing that's available.  Here we create special dataframes that include all the variables and their definitions and all the countries.  
Note the use of the drop_duplicates method, which does what it sounds like.
End of explanation
"""


ncunits = small['Units'] == 'National currency'
small[ncunits]

small[small['Units'] == 'National currency']

"""
Explanation: Exercise. 

Construct a list of countries with countries = weo[['ISO', 'Country']]; that is, without applying the drop_duplicates method.  How large is it?  How many duplicates have we dropped?  
What are the country codes (ISO) for Argentina, Germany, and Greece?  
What are the variable codes (WEO Subject Code) for government debt (gross debt, percent of GDP) and net lending/borrowing (also percent of GDP)?  

Comment. Now that we have the country and variable codes, we can be more explicit about what we want.  We want observations with those country and variable codes.  
We work up to the solution one step at a time.  
Comparisons for series
We can construct comparisons for dataframe columns much as we did with simple variables.  The difference is that we get a complete column or True/False responses, not just one.  
Mutiple comparisons have a different syntax than we saw earlier.  and is replaced by &amp;, and or is replaced by |.  And when we have more than comparison, we need to enclose them in parentheses.  
Here's an example.  
Exercise.  Compute and explain the comparisons:  

small['Units'] == 'National currency'
small['2011'] &gt;= 100
(small['Units'] == 'National currency') &amp; (small['2011'] &gt;= 100)
(small['Units'] == 'National currency') | (small['2011'] &gt;= 100)

Boolean selection
Boolean selection simply chooses those observations for which a condition is True.  Some people refer to this as filtering.  
Example.  We choose obervations for which the units are 'National currency'.  We do this first in two steps, then in one.
End of explanation
"""


vlist = ['GGXWDG_NGDP', 'GGXCNL_NGDP']
weo['WEO Subject Code'].isin(vlist).head(45)

"""
Explanation: Exercise. Construct dataframes for which 

small['Units'] does not equal 'National currency'.
small['Units'] equals 'National currency' and small['2011'] is greater than 100.  

<a id='isin'></a>
The isin method
Pay attention now, this is really useful.  Suppose we want to extract the data for which weo['ISO'] == 'ARG' (Argentina) or weo['ISO'] == 'GRC' (Greece).  We could do that by combining the comparisons:  
python
(weo['ISO'] == 'ARG') | (weo['ISO'] == 'GRC')
Remind youself that | stands for "or."  (What do we use for "and"?) 
A simpler approach is to apply the isin method to a variable.  This sets the comparison equal to True if the value of the observation is of weo['ISO'] equals any element in a list.  We could do the same thing using mulitple comparisons, but this is a lot easier.  
Let's see how this works.  
Example.  Let's apply the same logic to variable codes.  If we want to extract the observations with codes 
vlist = ['GGXWDG_NGDP', 'GGXCNL_NGDP']
we would use
End of explanation
"""


# this time let's use the result of isin for selection 
vlist = ['GGXWDG_NGDP', 'GGXCNL_NGDP']
weo[weo['WEO Subject Code'].isin(vlist)].head(6)

"""
Explanation: Comment. We're choosing 2 variables from 45, so there are lots of Falses.
End of explanation
"""


variables = ['GGXWDG_NGDP', 'GGXCNL_NGDP']
countries = ['ARG', 'DEU', 'GRC']
weo_sub = weo[weo['WEO Subject Code'].isin(variables) & weo['ISO'].isin(countries)]
weo_sub

"""
Explanation: Comment. We can do the same thing with countries.  If we want to choose two variables and three countries, the code looks like:
End of explanation
"""


# recall
ep['Media'].head(10)

# the contains method
ep['Media'].str.contains('Twitter').head(10)

"""
Explanation: Comments.

We've now done what we described when we applied the want operator. 
This is a go-to method.  Circle it for later reference.  
This is a go-to method.  Circle it for later reference.  

Exercise. Use the isin method to extract Gross domestic product in US dollars for China, India, and the United States.  Assign the result to the dataframe gdp.   
Exercise (challenging). Plot the variable gdp['2015'] as a bar chart.  What would you say it needs?  
<a id='contains'></a>
The contains method
Another useful one.  The contains string method for series identifies observations that contain a specific string.  If yes, the observation is labelled True, if no, False.  A little trick converts the True/False outcomes to ones and zeros.  
We apply it to the Media variable of the Entry Poll dataframe ep.  You may recall that this variable could have more than one response.  We tease them apart with the contains method.  Our want is to have a yes/no variable for each response.
End of explanation
"""


ep['Media'].str.contains('Twitter').head(10)*1

"""
Explanation: Comment. That's pretty good, we now know which students mentioned Twitter and which did not.  It's more useful, though, to convert this to zeros (False) and ones (True), which we do with this trick:  we multiply by 1.
End of explanation
"""


media = ['None', 'Twitter', 'Facebook', 'Blog'] 
oldep = ep.copy()

vnames = []
for x in media:
    newname = 'Media' + ':' + x 
    vnames.append(newname)
    ep[newname] = ep['Media'].str.contains(x)*1
    
vnames    

media = ep[vnames]
media.head()

media_counts = media.sum()
media_counts

media_counts.plot.barh()

"""
Explanation: Comment. Now let's do the same for some of the other entries and save them in new variables.
End of explanation
"""


data = {'Size': ['a) 1 to 4', 'b) 5 to 9', 'c) 10 to 19', 'd) 20 to 49', 'e) 50 to 99',
                 'f) 100 to 249', 'g) 250 to 499', 'h) 500 to 999', 'i) 1000 to 2499',
                 'j) 2500 to 4999', 'k) 5000 to 9999', 'l) 10000+'], 
        'Firms': [2846416, 1020772, 598153, 373345, 115544, 63845,
                  19389, 9588, 6088, 2287, 1250, 1357], 
        'Emp': [5998912, 6714924, 8151891, 11425545, 8055535, 9788341, 
                6611734, 6340775, 8321486, 6738218, 6559020, 32556671]}
bds = pd.DataFrame(data) 
bds .head(3) 

"""
Explanation: Exercise. What would you change in this graph?  How would you do it?  (Words are enough.) 
Review
Exercise. We explore the Census's Business Dynamics Statistics, a huge collection of data about firms. We've extracted a small piece of one of their databases that includes these variables for 2013:

Size: size category of firms based on number of employees
Firms: number of firms in each size category
Emp: number of employees in each size category

Run the code cell below to load the data.
End of explanation
"""


