Can not put a dataframe into hdfstore *completely*
- I load a dataframe from mysql: 

``` python
df_bugs_activity_4w = psql.read_frame('select * from bugs_activity limit 0, 40000', conn)
```
- and the structure of df_bugs_activity_4w:

``` python
In[19]: df_bugs_activity_4w
Out[19]:
<class 'pandas.core.frame.DataFrame'>
Int64Index: 40000 entries, 0 to 39999
Data columns:
bug_id       40000  non-null values
attach_id    13  non-null values
who          40000  non-null values
bug_when     40000  non-null values
fieldid      40000  non-null values
added        40000  non-null values
removed      40000  non-null values
id           40000  non-null values
dtypes: float64(1), int64(4), object(3)
```
- then, convert the object columns

``` python
In [60]: df_bugs_activity_4w = df_bugs_activity_4w.convert_objects()
In [61]: df_bugs_activity_4w
Out[61]:
<class 'pandas.core.frame.DataFrame'>
Int64Index: 40000 entries, 0 to 39999
Data columns:
bug_id       40000  non-null values
attach_id    13  non-null values
who          40000  non-null values
bug_when     40000  non-null values
fieldid      40000  non-null values
added        40000  non-null values
removed      40000  non-null values
id           40000  non-null values
dtypes: datetime64[ns](1), float64(1), int64(4), object(2)
```
- I put it into a hdfstore, and then get it out, found the number of dataframe entries changed from 40,000 to 13 ! That's weird. It seems that the number of 'attach_id' columns limits the total number of dataframe when putting it into a hdfstore.

```
In [63]: %prun store.put('df_bugs_activity_4w1', df_bugs_activity_4w, table=True)

In [64]: %time store.get('df_bugs_activity_4w1')
CPU times: user 0.00 s, sys: 0.00 s, total: 0.00 s
Wall time: 0.01 s
Out[64]:
bug_id  attach_id   who bug_when    fieldid added   removed id
2012     301879  0   35 1999-04-06 11:22:11  16  dev     bug     2013
2014     301879  0   35 1999-04-06 11:22:12  5   para    us 2015
2835     301879  0   56 1999-05-14 15:56:12  10  clo     op  2836
31244    301879  0   207    2001-07-18 14:11:38  10  op  clo     31245
31252    301879  0   207    2001-07-18 15:40:52  10  ana     op  31253
31283    301879  0   35 2001-07-18 21:21:33  16  lui     dev     31284
31285    301879  0   35 2001-07-18 21:21:34  15  296     10  31286
31287    301879  0   35 2001-07-18 21:21:35  5   unk     para    31288
31393    301879  0   159    2001-07-19 12:41:07  16  prat    lui     31394
31472    301879  0   207    2001-07-19 17:27:31  10  ope     ana     31473
32675    301879  0   207    2001-08-02 10:09:08  10  clos    op   32676
38609    235837  0   201    2001-09-26 20:28:11  15  310-    300-3   38610
38610    235838  0   201    2001-09-26 20:28:11  15  310-    300     38611
```

![2013-03-11 21:43:21 ](https://f.cloud.github.com/assets/1251601/243726/1484600a-8a52-11e2-9885-60a9992ce036.png)

```
In [66]: store
Out[66]:
<class 'pandas.io.pytables.HDFStore'>
File path: sample_no_fill.h5
/df_bugs_4w                      frame_table  (typ->appendable,nrows->40000,ncols->52,indexers->[index])
/df_bugs_4w1                     frame_table  (typ->legacy,nrows->None,ncols->0,indexers->[])           
/df_bugs_activity_4w             frame_table  (typ->appendable,nrows->13,ncols->8,indexers->[index])    
/df_bugs_activity_4w1            frame_table  (typ->appendable,nrows->13,ncols->8,indexers->[index]) 
```
- ps: I have posted this question on [stackoverflow](http://stackoverflow.com/questions/15271389/better-solution-when-dealing-with-the-missing-data-for-those-dataframe-objs-expo)
