Resample discards timezone information

[jeremywhelchel]

It appears that resample is now dropping timezone information on the index. Is this expected?

a = pp.Series(index=pp.DatetimeIndex(['2013-01-01 06:00', '2013-01-01 07:00', '2013-01-02 06:00'],
                                     tz=pytz.timezone('America/Los_Angeles')),
              data=[1, 2, 3])
b = a.resample('D', how='max')
print repr(a.index.tz)
print repr(b.index.tz)
print a.index.tz == b.index.tz

produces the following in 0.16.1. Notably the timezones for the original series and the resampled series are the same.

<DstTzInfo 'America/Los_Angeles' LMT-1 day, 16:07:00 STD>
<DstTzInfo 'America/Los_Angeles' LMT-1 day, 16:07:00 STD>
True

However that's not the case for 0.18.1. Caveat is that we're using the new resample syntax: b = a.resample('D').max()

<DstTzInfo 'America/Los_Angeles' LMT-1 day, 16:07:00 STD>
<DstTzInfo 'America/Los_Angeles' PST-1 day, 16:00:00 STD>
False

[jreback]

rewriting your example like how we test

In [10]: s = pd.Series(index=pd.DatetimeIndex(['2013-01-01 06:00', '2013-01-01 07:00', '2013-01-02 06:00'],
                                     tz='America/Los_Angeles'),
              data=[1, 2, 3])

In [11]: s
Out[11]: 
2013-01-01 06:00:00-08:00    1
2013-01-01 07:00:00-08:00    2
2013-01-02 06:00:00-08:00    3
dtype: int64

In [12]: s.index
Out[12]: DatetimeIndex(['2013-01-01 06:00:00-08:00', '2013-01-01 07:00:00-08:00', '2013-01-02 06:00:00-08:00'], dtype='datetime64[ns, America/Los_Angeles]', freq=None)

In [13]: s.resample('D').max()
Out[13]: 
2013-01-01 00:00:00-08:00    2
2013-01-02 00:00:00-08:00    3
Freq: D, dtype: int64

In [14]: s.resample('D').max().index
Out[14]: DatetimeIndex(['2013-01-01 00:00:00-08:00', '2013-01-02 00:00:00-08:00'], dtype='datetime64[ns, America/Los_Angeles]', freq='D')

datetime w/tz and resampling are not tested very much. pull-requests to do more of this are welcome (the fix is very straightforward).

[jeremywhelchel]

Thanks for the quick look!

Note that your re-written example doesn't display the problem. You need to look at repr(...index.tz) to see the difference (LMT-1 day, 16:07:00 STD vs PST-1 day, 16:00:00 STD)

[jreback]

have a look again at [12] vs [14]. the time changed. (look t the hour). the issue is the re-localization is off. The actual tz is correct.