ENH: Allow to reset tz from DatetimeIndex holding time representation

[sinhrks]

There looks no easy way to remove tz from tz-aware DatetimeIndex holding the timestamp represented. What required is inverse operation of tz_localize.

idx = pd.date_range('2014-01-01 09:00', '2014-01-01 20:00', freq='H', tz='Asia/Tokyo')
idx
# <class 'pandas.tseries.index.DatetimeIndex'>
# [2014-01-01 09:00:00+09:00, ..., 2014-01-01 20:00:00+09:00]
# Length: 12, Freq: H, Timezone: Asia/Tokyo

# What I want to do is:
idx.tz_reset()
# <class 'pandas.tseries.index.DatetimeIndex'>
# [2014-01-01 09:00:00, ..., 2014-01-01 20:00:00]
# Length: 12, Freq: H, Timezone: None

# This raises TypeError
idx.tz_localize(None)
# TypeError: Already tz-aware, use tz_convert to convert.

# This change the timestamp to UTC
idx.tz_convert(None)
# <class 'pandas.tseries.index.DatetimeIndex'>
# [2014-01-01 00:00:00, ..., 2014-01-01 11:00:00]
# Length: 12, Freq: H, Timezone: None

In my case, there are some globally distributed data sources which holds local timezones. And want to merge them and analyze based on local subjective times (business hours, etc).

[rockg]

+1. What if we support idx.tzinfo=None and that operates appropriately on the underlying data?

[jreback]

I agree with @rockg (maybe idx.tz = None though).

I don't think this very common, so full function I don't think is necessary (though I guess can't hurt).

[nehalecky]

+1 : I suspect this is more common than imagined. :)

[jreback]

@nehalecky hahh!

ok, so method and setter?

how do you do this now?

DatetimeIndex(idx_with_tz.tz_convert('UTC'),tz=None) ?

[sinhrks]

Initial idea may be generalized by adding force option to tz_localize.

idx = pd.date_range('2014-01-01 09:00', '2014-01-01 20:00', freq='H', tz='Asia/Tokyo')
idx
# <class 'pandas.tseries.index.DatetimeIndex'>
# [2014-01-01 09:00:00+09:00, ..., 2014-01-01 20:00:00+09:00]
# Length: 12, Freq: H, Timezone: Asia/Tokyo

# TypeError by default
idx.tz_localize(None)
# TypeError: Already tz-aware, use tz_convert to convert.

idx.tz_localize(None, force=True)
# <class 'pandas.tseries.index.DatetimeIndex'>
# [2014-01-01 09:00:00, ..., 2014-01-01 20:00:00]
# Length: 12, Freq: H, Timezone: None

# can be used to set different timezones with same representation
idx.tz_localize('US/Eastern', force=True)
# <class 'pandas.tseries.index.DatetimeIndex'>
# [2014-01-01 09:00:00-05:00, ..., 2014-01-01 20:00:00-05:00]
# Length: 12, Freq: H, Timezone: US/Eastern

[jreback]

what about just allowing tz_localize(None) as a valid argument and/or (tz_convert(None))

though this may be more confusing

[rockg]

I think None is a great idea and I don't think it's too confusing.

[jreback]

should this work only on one if tz_convert/tz_localize?

side issue do we support setting directly of a tz? (which would convert/localize as appropriate)

[rockg]

I was going to say just tz_localize before but it probably does make more sense with tz_convert (converting a tz to a non-tz). I think supporting both is okay. I don't think we support directly setting tz except through tz_localize.

[jreback]

ok, so:

• need to figure out what cases the currently raised error is actually useful (e.g. wesm must have put it their for some reason - maybe just to remind the user)?
• raise NotImplementedError on directly setting tz if we are not going to allow it (I actually think its ok, maybe just a call to tz_convert(tz)