Re-fetching with "how = count" causes problems

Question

I have a simple pandas framework that has measurements at different times:

                     volume
t
2013-10-13 02:45:00      17
2013-10-13 05:40:00      38
2013-10-13 09:30:00      29
2013-10-13 11:40:00      25
2013-10-13 12:50:00      11
2013-10-13 15:00:00      17
2013-10-13 17:10:00      15
2013-10-13 18:20:00      12
2013-10-13 20:30:00      20
2013-10-14 03:45:00       9
2013-10-14 06:40:00      30
2013-10-14 09:40:00      43
2013-10-14 11:05:00      10

I am doing basic resampling and plotting, for example a daily total, which works fine:

df.resample('D',how='sum').head()   

            volume
t
2013-10-13     184
2013-10-14     209
2013-10-15     197
2013-10-16     309
2013-10-17     317

But for some reason, when I try to make the total number of records per day, it returns a series with multiple indices instead of a data frame:

df.resample('D',how='count').head()

2013-10-13  volume     9
2013-10-14  volume     9
2013-10-15  volume     7
2013-10-16  volume     9
2013-10-17  volume    10

I can correct the data so that it can be easily applied using a simple non-stationary call, i.e. df.resample('D',how='count').unstack()but why does calling with a resample using how='count'have a different behavior than with how='sum'?

Answer 1

, resample count (, , 0,13.1). . , : Count Resampling mutli-ndex

 :

>>> df
                     volume
date                       
2013-10-13 02:45:00      17
2013-10-13 05:40:00      38
2013-10-13 09:30:00      29
2013-10-13 11:40:00      25
2013-10-13 12:50:00      11
2013-10-13 15:00:00      17
2013-10-13 17:10:00      15
2013-10-13 18:20:00      12
2013-10-13 20:30:00      20
2013-10-14 03:45:00       9
2013-10-14 06:40:00      30
2013-10-14 09:40:00      43
2013-10-14 11:05:00      10

, :

>>> df.resample('D',how='count')

2013-10-13  volume    9
2013-10-14  volume    4

, , count volume dict resample:

>>> df.resample('D',how={'volume':'count'})

            volume
date              
2013-10-13       9
2013-10-14       4