熊猫TimeGrouper按列

Question

I have a csv file with dates as columns headers and binary a matrix of 1, 0 or np.nan .

I'd like to take the mean of each index, grouped by month. I am running into a problem because my columns are not a datetimeindex, which I try to convert to with pd.to_datetime() with no luck.

binary.csv:

2016-01-01 00:00:00,2016-01-02 00:00:00,2016-02-01 00:00:00,2016-02-02 00:00:00
1,,0,1
0,1,,1

My Code:

import pandas as pd
import numpy as np

df = pd.read_csv('binary.csv')
df.columns = pd.to_datetime(df.columns, format='%Y-%m-%d %H:%M:%S')
df = df.groupby(pd.TimeGrouper(freq='M'), axis=0)
print df

Error:

TypeError: axis must be a DatetimeIndex, but got an instance of 'Int64Index'

Desired Output:

   2016-01-01 00:00:00  2016-02-01 00:00:00
0                  1.0                  0.5
1                  0.5                  1.0

Updated question:

Based on best answer:

If I wanted to a single value for each month, is there a more efficient way to do that than this?

pd.DataFrame(data=df.resample('MS', axis=1).mean().mean()).transpose()

Answer 1

By default, pd.TimeGrouper works on the index (axis=0) so you need to tell it that it should group the columns instead:

df.groupby(pd.TimeGrouper(freq='MS', axis=1), axis=1).mean()
Out: 
   2016-01-01  2016-02-01
0         1.0         0.5
1         0.5         1.0

You can directly use resample, too:

df.resample('MS', axis=1).mean()
Out: 
   2016-01-01  2016-02-01
0         1.0         0.5
1         0.5         1.0