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BUG: Keep categorical name in groupby #28798

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Merged
merged 6 commits into from
Oct 7, 2019
Merged

BUG: Keep categorical name in groupby #28798

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3a130f4
BUG: Keep categorical name in groupby
Oct 5, 2019
1f133ac
Add assert
Oct 5, 2019
14da79d
Change test
Oct 5, 2019
f1960b4
Update test
Oct 6, 2019
56c5122
Use check_like in test
Oct 6, 2019
1b471b7
Set column order
Oct 7, 2019
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1 change: 1 addition & 0 deletions doc/source/whatsnew/v1.0.0.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -284,6 +284,7 @@ Groupby/resample/rolling
- Bug in :meth:`DataFrame.rolling` not allowing for rolling over datetimes when ``axis=1`` (:issue: `28192`)
- Bug in :meth:`DataFrame.groupby` not offering selection by column name when ``axis=1`` (:issue:`27614`)
- Bug in :meth:`DataFrameGroupby.agg` not able to use lambda function with named aggregation (:issue:`27519`)
- Bug in :meth:`DataFrame.groupby` losing column name information when grouping by a categorical column (:issue:`28787`)

Reshaping
^^^^^^^^^
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3 changes: 2 additions & 1 deletion pandas/core/groupby/grouper.py
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Expand Up @@ -330,7 +330,8 @@ def __init__(
self._group_index = CategoricalIndex(
Categorical.from_codes(
codes=codes, categories=categories, ordered=self.grouper.ordered
)
),
name=self.name,
)

# we are done
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26 changes: 23 additions & 3 deletions pandas/tests/groupby/test_categorical.py
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Expand Up @@ -674,7 +674,7 @@ def test_preserve_categories():

# ordered=True
df = DataFrame({"A": Categorical(list("ba"), categories=categories, ordered=True)})
index = CategoricalIndex(categories, categories, ordered=True)
index = CategoricalIndex(categories, categories, ordered=True, name="A")
tm.assert_index_equal(
df.groupby("A", sort=True, observed=False).first().index, index
)
Expand All @@ -684,8 +684,8 @@ def test_preserve_categories():

# ordered=False
df = DataFrame({"A": Categorical(list("ba"), categories=categories, ordered=False)})
sort_index = CategoricalIndex(categories, categories, ordered=False)
nosort_index = CategoricalIndex(list("bac"), list("bac"), ordered=False)
sort_index = CategoricalIndex(categories, categories, ordered=False, name="A")
nosort_index = CategoricalIndex(list("bac"), list("bac"), ordered=False, name="A")
tm.assert_index_equal(
df.groupby("A", sort=True, observed=False).first().index, sort_index
)
Expand Down Expand Up @@ -1193,3 +1193,23 @@ def test_groupby_categorical_axis_1(code):
result = df.groupby(cat, axis=1).mean()
expected = df.T.groupby(cat, axis=0).mean().T
assert_frame_equal(result, expected)


def test_groupby_cat_preserves_structure():
# GH 28787
df = DataFrame({"Name": ["Bob", "Greg"], "Item": [1, 2]})
expected = (
df.groupby("Name", observed=True)
.agg(pd.DataFrame.sum, skipna=True)
.reset_index()
)
expected["Name"] = expected["Name"].astype("category")

df["Name"] = df["Name"].astype("category")
result = (
df.groupby("Name", observed=True)
.agg(pd.DataFrame.sum, skipna=True)
.reset_index()
)

assert_frame_equal(result, expected)