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GH24241 make Categorical.map transform nans #24275

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Merged
merged 5 commits into from
Dec 20, 2018
Merged

GH24241 make Categorical.map transform nans #24275

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d765dc3
BUG-24241 make Categorical.map transform nans
JustinZhengBC Dec 13, 2018
628bfac
BUG-24241 make requested changes
JustinZhengBC Dec 15, 2018
2011996
BUG-24241 update documentation instead
JustinZhengBC Dec 19, 2018
e5b5415
BUG-24241 add comment
JustinZhengBC Dec 19, 2018
82859d9
BUG-24241 use np.any instead of any
JustinZhengBC Dec 20, 2018
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1 change: 1 addition & 0 deletions doc/source/whatsnew/v0.24.0.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -1273,6 +1273,7 @@ Categorical
- Bug when resampling :meth:`Dataframe.resample()` and aggregating on categorical data, the categorical dtype was getting lost. (:issue:`23227`)
- Bug in many methods of the ``.str``-accessor, which always failed on calling the ``CategoricalIndex.str`` constructor (:issue:`23555`, :issue:`23556`)
- Bug in :meth:`Series.where` losing the categorical dtype for categorical data (:issue:`24077`)
- Bug in :meth:`Categorical.apply` where the given function would not be applied to ``NaN`` values (:issue:`24241`)

Datetimelike
^^^^^^^^^^^^
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21 changes: 18 additions & 3 deletions pandas/core/arrays/categorical.py
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Expand Up @@ -1229,11 +1229,26 @@ def map(self, mapper):
Index(['first', 'second', nan], dtype='object')
"""
new_categories = self.categories.map(mapper)

try:
return self.from_codes(self._codes.copy(),
categories=new_categories,
ordered=self.ordered)
if is_dict_like(mapper):
new_value = mapper[np.nan]
else:
new_value = mapper(np.nan)
except (AttributeError, KeyError, TypeError, ValueError):
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I'm not really comfortable with this. mapper is a user-defined function. Consider

def f(x):
    if isnan(x):
        raise TypeError
    ...

that TypeError would be swallowed by pandas.

new_value = np.nan

try:
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why are you try/except here?

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how / why can this fail

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@JustinZhengBC JustinZhengBC Dec 15, 2018 •
edited
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AttributeError: if mapper calls a method of the element (e.g. lambda x: x.lower())
KeyError: if mapper is a dict without a key for NaN
TypeError: if mapper expects some type other than a float
ValueError: if mapper tries converting float values to ints (e.g. lambda x: int(x))

if you mean the try/except below that, that was already there. from_codes raises a ValueError if the mapping isn't one-to-one

ret = self.from_codes(self._codes.copy(),
categories=new_categories,
ordered=self.ordered)
if new_value not in ret.categories and any(self._codes == -1):
ret.add_categories(new_value, inplace=True)
ret = ret.fillna(new_value)
return ret
except ValueError:
new_categories = new_categories.insert(len(new_categories),
new_value)
return np.take(new_categories, self._codes)

__eq__ = _cat_compare_op('__eq__')
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38 changes: 38 additions & 0 deletions pandas/tests/indexes/test_category.py
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Expand Up @@ -311,6 +311,44 @@ def test_map_with_categorical_series(self):
exp = pd.Index(["odd", "even", "odd", np.nan])
tm.assert_index_equal(a.map(c), exp)

@pytest.mark.parametrize(
(
'data',
'f'
),
(
([1, 1, np.nan], pd.isna),
([1, 2, np.nan], pd.isna),
([1, 1, np.nan], {1: False, np.nan: True}),
([1, 2, np.nan], {1: False, 2: False, np.nan: True})
))
def test_map_fill_nan(self, data, f): # GH 24241
values = pd.Categorical(data)
result = values.map(f)
if data[1] == 1:
expected = pd.Categorical([False, False, True])
tm.assert_categorical_equal(result, expected)
else:
expected = pd.Index([False, False, True])
tm.assert_index_equal(result, expected)

@pytest.mark.parametrize(
(
'data',
'f'
),
(
([1, 1, np.nan], {1: False}),
([1, 2, np.nan], {1: False, 2: False}),
([1, 1, np.nan], pd.Series([False, False])),
([1, 2, np.nan], pd.Series([False, False, False]))
))
def test_map_dont_fill_nan(self, data, f): # GH 24241
values = pd.Categorical(data)
result = values.map(f)
expected = pd.Index([False, False, np.nan])
tm.assert_index_equal(result, expected)

@pytest.mark.parametrize('klass', [list, tuple, np.array, pd.Series])
def test_where(self, klass):
i = self.create_index()
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