DataFrame groupby partially drops timezone info (to_csv, in notebook)
Hi all,

I've encountered a problem with DataFrames, groupby and timezones.

import pandas as pd
import numpy as np

dt_rng = pd.date_range(start='2014-01-01 00:00', periods = 1000, freq='1s', tz='Europe/Berlin')
df = pd.DataFrame({'a':np.random.randn(1000), 'b': np.random.randn(1000)},index = dt_rng)
df['b'] = df['b'].round()
df.to_csv()

--> Timezones are shown in the csv output, for example 2014-01-01 00:00:00+01:00

Now with resampling:

dt_rng = pd.date_range(start='2014-01-01 00:00', periods = 1000, freq='1s', tz='Europe/Berlin')
df = pd.DataFrame({'a':np.random.randn(1000), 'b': np.random.randn(1000)},index = dt_rng)
df['b'] = df['b'].round()
df.groupby(df['b']).resample('1min').to_csv()

--> 2013-12-31 23:01:00 no timezone info, not even UTC.

However:

dt_rng = pd.date_range(start='2014-01-01 00:00', periods = 1000, freq='1s', tz='Europe/Berlin')
df = pd.DataFrame({'a':np.random.randn(1000), 'b': np.random.randn(1000)},index = dt_rng)
df['b'] = df['b'].round()
df.groupby(df['b']).resample('1min').index.levels[1]

shows: Timezone: Europe/Berlin

So the info seems to be there, but is not exported - even if it was exported before without resampling...

Any ideas?

Thanks and best regards
