BUG: GH15429 transform result of timedelta from datetime #15430

stephenrauch · 2017-02-16T22:13:26Z

The transform() operation needs to return a like-indexed. To facilitate this, transform starts with a copy of the original series. Then, after the computation for each group, sets the appropriate elements of the copied series equal to the result. At that point is does a type comparison, and discovers that the timedelta is not cast-able to a datetime.

closes BUG: output of a transform is cast to dtype of input #10972
tests added / passed
passes git diff upstream/master | flake8 --diff
whatsnew entry

codecov-io · 2017-02-17T05:56:58Z

Codecov Report

Merging #15430 into master will decrease coverage by -0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master   #15430      +/-   ##
==========================================
- Coverage   90.36%   90.36%   -0.01%     
==========================================
  Files         136      136              
  Lines       49553    49555       +2     
==========================================
+ Hits        44780    44781       +1     
- Misses       4773     4774       +1

Impacted Files	Coverage Δ
pandas/core/groupby.py	`94.99% <100%> (ø)`	✅
pandas/util/testing.py	`81.91% <0%> (-0.19%)`	❌
pandas/types/cast.py	`85.65% <0%> (+0.23%)`	✅

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jreback · 2017-02-17T14:30:18Z

instead of this, use pandas.type.cast._find_common_type rather than np.common_type; that is some old code.

jreback · 2017-02-17T14:32:14Z

your bug report is the same as this: #10972

so please add these as tests cases.

jreback · 2017-02-17T14:33:29Z

doc/source/whatsnew/v0.20.0.txt

@@ -579,6 +579,8 @@ Bug Fixes



+- Bug in ``groupby.transform`` where calculating a ``timedelta`` from a ``datetime`` caused a ``ValueError`` (:issue:`15429`)


add 10972 as well (you can leave the other issue as well)

jreback · 2017-02-23T13:27:15Z

can you update

stephenrauch · 2017-02-27T08:09:27Z

I tried to use pandas.type.cast._find_common_type rather than np.common_type in the function where this work was done, but one of the other test cases broke. I looked at it, but didn't undertsand it well enough to know how to fix.

jreback · 2017-02-27T13:22:02Z

doc/source/whatsnew/v0.20.0.txt

@@ -624,7 +624,8 @@ Bug Fixes
 - Bug in ``pd.concat()`` in which concatting with an empty dataframe with ``join='inner'`` was being improperly handled (:issue:`15328`)


-
+- Bug in ``groupby.transform`` where calculating a ``timedelta`` from a ``datetime`` caused a ``ValueError`` (:issue:`15429`)


just do a single note with the issue number. make this simpler, something like: .transform incorrectly changing the dtype of the output.

jreback · 2017-02-27T13:23:00Z

pandas/core/groupby.py

@@ -2906,8 +2906,15 @@ def transform(self, func, *args, **kwargs):
                common_type = np.common_type(np.array(res), result)
                if common_type != result.dtype:
                    result = result.astype(common_type)
-            except:
-                pass
+            except Exception as exc:


huh? this is way complicated

Sorry, this was a line I put into to see why the change to _find_common_type was causing problems.

jorisvandenbossche · 2017-02-27T13:38:05Z

I looked at it, but didn't undertsand it well enough to know how to fix.

@stephenrauch Which test broke when you used _find_common_type? Can you try to describe the problem a bit more in detail?
(also, if you add new commits to a PR instead of amending it to the first, it is easier to see what you changed and to comment on those steps)

jreback · 2017-02-27T13:43:59Z

@stephenrauch I have a fix for this which avoids all of this complication. I will push soon.

jreback · 2017-02-27T14:32:50Z

@stephenrauch ok (aside from a flake issue) I think this should work. But if you'd run the perf suite for groupby to see that wasn't changed too much. IIRC that's the reason we did the inplace indexing; and I think that was before we did the fast_transform anyhow (which is now a different path), so this maybe be ok.

The transform() operation needs to return a like-indexed. To facilitate this, transform starts with a copy of the original series. Then, after the computation for each group, sets the appropriate elements of the copied series equal to the result. At that point is does a type comparison, and discovers that the timedelta is not cast-able to a datetime.

The transform() operation needs to return a like-indexed. To facilitate this, transform starts with a copy of the original series. Then, after the computation for each group, sets the appropriate elements of the copied series equal to the result. At that point is does a type comparison, and discovers that the timedelta is not cast- able to a datetime. closes pandas-dev#10972 Author: Jeff Reback <[email protected]> Author: Stephen Rauch <[email protected]> Closes pandas-dev#15430 from stephenrauch/group-by-transform-timedelta-from-datetime and squashes the following commits: c3b0dd0 [Jeff Reback] PEP fix 2f48549 [Jeff Reback] fixup slow transforms cc43503 [Stephen Rauch] BUG: GH15429 transform result of timedelta from datetime

jreback · 2017-02-27T21:38:46Z

thanks @stephenrauch I merged this (I actually needed some more fixes for making sure .agg didn't do the same thing). And perf testing was about the same.

The transform() operation needs to return a like-indexed. To facilitate this, transform starts with a copy of the original series. Then, after the computation for each group, sets the appropriate elements of the copied series equal to the result. At that point is does a type comparison, and discovers that the timedelta is not cast- able to a datetime. closes pandas-dev#10972 Author: Jeff Reback <[email protected]> Author: Stephen Rauch <[email protected]> Closes pandas-dev#15430 from stephenrauch/group-by-transform-timedelta-from-datetime and squashes the following commits: c3b0dd0 [Jeff Reback] PEP fix 2f48549 [Jeff Reback] fixup slow transforms cc43503 [Stephen Rauch] BUG: GH15429 transform result of timedelta from datetime

jreback added Bug Groupby Dtype Conversions Unexpected or buggy dtype conversions labels Feb 17, 2017

jreback reviewed Feb 17, 2017

View reviewed changes

stephenrauch force-pushed the group-by-transform-timedelta-from-datetime branch from 4e790f6 to e0004e7 Compare February 27, 2017 08:06

stephenrauch force-pushed the group-by-transform-timedelta-from-datetime branch from e0004e7 to eb0f498 Compare February 27, 2017 08:13

jreback reviewed Feb 27, 2017

View reviewed changes

stephenrauch and others added 3 commits February 27, 2017 10:39

fixup slow transforms

2f48549

PEP fix

c3b0dd0

jreback force-pushed the group-by-transform-timedelta-from-datetime branch from 05d573e to c3b0dd0 Compare February 27, 2017 15:39

jreback added this to the 0.20.0 milestone Feb 27, 2017

jreback closed this in 251826f Feb 27, 2017

chris-b1 mentioned this pull request Jul 10, 2017

BUG: coercing of bools in groupby transform #16875

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BUG: GH15429 transform result of timedelta from datetime #15430

BUG: GH15429 transform result of timedelta from datetime #15430

stephenrauch commented Feb 16, 2017 •

edited by jreback

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codecov-io commented Feb 17, 2017 •

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jorisvandenbossche commented Feb 27, 2017

jreback commented Feb 27, 2017

jreback commented Feb 27, 2017

jreback commented Feb 27, 2017

		@@ -579,6 +579,8 @@ Bug Fixes



		- Bug in ``groupby.transform`` where calculating a ``timedelta`` from a ``datetime`` caused a ``ValueError`` (:issue:`15429`)

		@@ -624,7 +624,8 @@ Bug Fixes
		- Bug in ``pd.concat()`` in which concatting with an empty dataframe with ``join='inner'`` was being improperly handled (:issue:`15328`)



		- Bug in ``groupby.transform`` where calculating a ``timedelta`` from a ``datetime`` caused a ``ValueError`` (:issue:`15429`)

BUG: GH15429 transform result of timedelta from datetime #15430

BUG: GH15429 transform result of timedelta from datetime #15430

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