BUG: Add test for pandas-dev#28641 to ensure that error does not occu…

…r again
phofl · Mar 28, 2020 · 35a4dd6 · 35a4dd6
1 parent e88c392
commit 35a4dd6
Show file tree

Hide file tree

Showing 2 changed files with 15 additions and 0 deletions.
diff --git a/pandas/tests/groupby/aggregate/test_aggregate.py b/pandas/tests/groupby/aggregate/test_aggregate.py
@@ -773,6 +773,13 @@ def test_aggregate_mixed_types():
     tm.assert_frame_equal(result, expected)
 
 
+def test_aggregate_categorical_lost_index():
+    # GH: 28641
+    result = pd.DataFrame({"A": [1997], "B": pd.Series(["b"], dtype="category").cat.as_ordered()}).groupby("A").agg({"B": "min"})
+    expected = pd.DataFrame({"B": ["b"]}, index=pd.Index([1997], name="A"))
+    tm.assert_frame_equal(result, expected)
+
+
 @pytest.mark.xfail(reason="Not implemented.")
 def test_aggregate_udf_na_extension_type():
     # https://github.com/pandas-dev/pandas/pull/31359

diff --git a/pandas/tests/groupby/test_categorical.py b/pandas/tests/groupby/test_categorical.py
@@ -1380,3 +1380,11 @@ def test_groupby_agg_non_numeric():
 
     result = df.groupby([1, 2, 1]).nunique()
     tm.assert_frame_equal(result, expected)
+
+
+def test_groupy_first_returns_categorical():
+    # GH 28641: Issue mentioned in first comment.
+    df = pd.DataFrame({"A": [1997], "B": pd.Series(["b"], dtype="category").cat.as_ordered()})
+    result = df.groupby("A")["B"].first()
+    expected = pd.Series(["b"], index=pd.Index([1997], name="A"), name="B")
+    tm.assert_series_equal(result, expected)