ENH: support .strftime for datetimelikes (closes #10086) #10110

mortada · 2015-05-12T06:42:39Z

jreback · 2015-05-12T10:46:56Z

this works for DatetimeIndex, something broken for PeriodIndex. And should not work for TimedeltaIndex (as I don't think the strftime codes are meaningful). Further want to actually define .strftime on the index itself as well (maybe def strftime(self, format):).

needs tests for the same

mortada · 2015-05-13T00:55:42Z

that makes sense

I've added to both DatetimeIndex and PeriodIndex. Also added a few tests.

jreback · 2015-05-13T01:00:30Z

pls add strftime to API.rst
also I think a mini section in time series.rst would be ok too

jreback · 2015-05-13T11:39:22Z

pandas/tseries/index.py

@@ -694,6 +694,21 @@ def astype(self, dtype):
        else:  # pragma: no cover
            raise ValueError('Cannot cast DatetimeIndex to dtype %s' % dtype)

+    def strftime(self, date_format):


hmm, not to make this more complicated, but maybe move to tseries/base/DatelikeOps (new mixin), that both DatetimeIndex/PeriodIndex, but NOT TimedeltaIndex inherit from.

I thought about something like that too, good idea for code reuse! Will update shortly

mortada · 2015-05-14T00:18:31Z

@jreback it's updated

mortada · 2015-06-01T02:58:23Z

@jreback I added a mini section to basics.rst instead, but otherwise this is ready for review

jreback · 2015-06-01T10:48:09Z

doc/source/basics.rst

@@ -1164,12 +1164,28 @@ You can also chain these types of operations:

   s.dt.tz_localize('UTC').dt.tz_convert('US/Eastern')

+You can also format the datetime values with ``Series.dt.strftime``:
+


maybe be explict and say that this is a string

jreback · 2015-06-26T23:42:21Z

can you update for comments. also related to #10442. I want this method to be the 'primary' date-string formatting (though .astype(str) will be supported by calling what this calls, namely .format), but this should be the goto method

copy your example that you added to basics.rst and put in 0.17.0 (in a separate section, maybe datetime-string formatting or somesuch)

mortada · 2015-06-27T02:50:53Z

@jreback updated according to your comments except for one thing: I couldn't actually find an invalid formatting string that would cause strftime to raise an exception

jreback · 2015-06-27T12:14:02Z

doc/source/basics.rst

@@ -1238,12 +1238,28 @@ You can also chain these types of operations:

   s.dt.tz_localize('UTC').dt.tz_convert('US/Eastern')

+You can also format datetime values as strings with ``Series.dt.strftime``:
+
+.. ipython:: python


can u add a reference to the standard library docs for the strftime format here

jreback · 2015-06-27T14:36:55Z

doc/source/whatsnew/v0.17.0.txt

@@ -32,6 +32,23 @@ Other enhancements
 ^^^^^^^^^^^^^^^^^^

 - ``.as_blocks`` will now take a ``copy`` optional argument to return a copy of the data, default is to copy (no change in behavior from prior versions), (:issue:`9607`)
+- Support ``.strftime`` for datetime-likes (:issue:`10110`)
+
+For example:


I think this all needs to be indented 2 spaces (to form a sub-block)

jorisvandenbossche · 2015-07-29T20:13:31Z

We also have a tslib.format_array_from_datetime function. Can you check if this is faster? (also uses strftime, but the loop is cythonized)

mortada · 2015-07-30T13:44:25Z

@jorisvandenbossche sure I'll check

jreback · 2015-07-30T14:44:33Z

pandas/tseries/period.py

        imask = ~mask
-        values[imask] = np.array([u('%s') % dt for dt in values[imask]])
+
+        formatter = lambda dt: dt.strftime(date_format) if date_format else u('%s') % dt


put the if on the outside (and lambdas on the inside), then check is only done once

jreback · 2015-07-30T14:45:58Z

@jorisvandenbossche this calls .format(date_format=...) which ultimately calls the cython tslib.format_array_from_datetime, so this is just syntatic sugar.

mortada · 2015-07-30T16:30:25Z

@jreback reordered the lambdas and the if/else as you suggested, also added more unit tests

jreback · 2015-07-30T16:44:03Z

ok, lgtm. ping when green.

mortada · 2015-07-30T16:46:43Z

sure will do

jorisvandenbossche · 2015-07-30T17:15:07Z

doc/source/basics.rst

@@ -1280,12 +1280,29 @@ You can also chain these types of operations:

   s.dt.tz_localize('UTC').dt.tz_convert('US/Eastern')

+You can also format datetime values as strings with ``Series.dt.strftime`` which


you can use :meth:Series.dt.strftime`` here as well, then it makes the link to the doc page

although that is maybe not that important here as it is exactly the same as standard library

sure will do

mortada · 2015-07-31T13:27:57Z

@jorisvandenbossche @jreback updated to return ndarray instead of list

mortada · 2015-08-02T05:02:19Z

@jorisvandenbossche @jreback it's green now, please take a look

jreback · 2015-08-02T14:57:29Z

pandas/tseries/tests/test_timeseries.py

@@ -2362,7 +2362,7 @@ def test_map(self):
        f = lambda x: x.strftime('%Y%m%d')
        result = rng.map(f)
        exp = [f(x) for x in rng]
-        self.assert_numpy_array_equal(result, exp)
+        np.testing.assert_array_equal(result, exp)


change back. we don't use np.testing.* directly

@jreback I changed it because assert_numpy_array_equal() actually would fail in some of the testing environments. It seems like a problem with the older numpy version (1.8.x)

what should I change it to instead?

ahh, you are not comparing numpy arrays (they are actually a list and an array), use exp = np.asarray(....) and I think it will work, you can also try tm.assert_almost_equal(...)

scratch that first part, use tm.assert_almost_equal; I though you were comparing the output of .strftime which was an np.array

ah cool I think tm.assert_almost_equal works, thanks! will update shortly

jreback · 2015-08-02T14:58:33Z

@mortada couple of comments. ping when green.

mortada · 2015-08-03T03:15:34Z

@jreback updated, please take a look

jreback · 2015-08-03T12:42:46Z

thanks!

jreback added Enhancement Output-Formatting __repr__ of pandas objects, to_string labels May 12, 2015

jreback added this to the 0.17.0 milestone May 12, 2015

jreback added Datetime Datetime data dtype Strings String extension data type and string data labels May 12, 2015

mortada force-pushed the dt_strftime branch from 1c5e466 to e27b9cb Compare May 13, 2015 00:47

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jorisvandenbossche mentioned this pull request Jun 26, 2015

ENH: Convert datetimelike index to strings with astype(str) #10442

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ENH: support .strftime for datetimelikes (closes pandas-dev#10086)

4348781

mortada force-pushed the dt_strftime branch from a5625b0 to 4348781 Compare August 2, 2015 16:29

jreback merged commit 4348781 into pandas-dev:master Aug 3, 2015

mortada deleted the dt_strftime branch August 3, 2015 12:45

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ENH: support .strftime for datetimelikes (closes #10086) #10110

ENH: support .strftime for datetimelikes (closes #10086) #10110

mortada commented May 12, 2015

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jreback commented Aug 3, 2015

		@@ -1164,12 +1164,28 @@ You can also chain these types of operations:

		s.dt.tz_localize('UTC').dt.tz_convert('US/Eastern')

		You can also format the datetime values with ``Series.dt.strftime``:

		@@ -1280,12 +1280,29 @@ You can also chain these types of operations:

		s.dt.tz_localize('UTC').dt.tz_convert('US/Eastern')

		You can also format datetime values as strings with ``Series.dt.strftime`` which

ENH: support .strftime for datetimelikes (closes #10086) #10110

ENH: support .strftime for datetimelikes (closes #10086) #10110

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