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BUG: Fixed NDFrame.transform('abs') #20800

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Merged
merged 3 commits into from
Apr 25, 2018
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BUG: Fixed NDFrame.transform('abs') #20800

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6f05eba
BUG: Fixed NDFrame.transform('abs')
TomAugspurger Apr 23, 2018
b26e5b2
REF: inspect function signature
TomAugspurger Apr 24, 2018
715ac25
parametrized test
TomAugspurger Apr 25, 2018
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3 changes: 3 additions & 0 deletions pandas/core/apply.py
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Original file line number Diff line number Diff line change
Expand Up @@ -111,6 +111,9 @@ def get_result(self):

# string dispatch
if isinstance(self.f, compat.string_types):
# Support for `frame.transform('method')`
# Some methods (shift, etc.) require the axis argument, others
# don't, so inspect and insert if nescessary.
func = getattr(self.obj, self.f)
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much better, and now IIRC we actually do something like this in groupby apply (for the same reason). can you add some comments here on what is going on

sig = compat.signature(func)
if 'axis' in sig.args:
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10 changes: 7 additions & 3 deletions pandas/tests/frame/test_apply.py
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Expand Up @@ -4,6 +4,7 @@

import pytest

import operator
from datetime import datetime

import warnings
Expand Down Expand Up @@ -880,11 +881,14 @@ def f():
with np.errstate(all='ignore'):
df.agg({'A': ['abs', 'sum'], 'B': ['mean', 'max']})

def test_transform_abs_name(self):
@pytest.mark.parametrize('method', [
'abs', 'shift', 'pct_change', 'cumsum', 'rank',
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Could also add ffill and bfill

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Splitting to #20821

])
def test_transform_method_name(self, method):
# https://github.com/pandas-dev/pandas/issues/19760
df = pd.DataFrame({"A": [-1, 2]})
result = df.transform('abs')
expected = pd.DataFrame({"A": [1, 2]})
result = df.transform(method)
expected = operator.methodcaller(method)(df)
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Learned something new today. Just out of curiosity, is this any different from doing getattr(df, method)()?

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in this case, no. methodcaller is nicer though when you need to bind parameters, but don't have the object yet (common in pytest fixtures).

tm.assert_frame_equal(result, expected)

def test_demo(self):
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