REGR: Resampler.aggregate fails when used with column selection

doc/source/whatsnew/v1.3.3.rst

@@ -22,6 +22,7 @@ Fixed regressions
 - Fixed regression in :meth:`RangeIndex.where` and :meth:`RangeIndex.putmask` raising ``AssertionError`` when result did not represent a :class:`RangeIndex` (:issue:`43240`)
 - Fixed regression in :meth:`read_parquet` where the ``fastparquet`` engine would not work properly with fastparquet 0.7.0 (:issue:`43075`)
 - Fixed regression in :func:`is_list_like` where objects with ``__iter__`` set to ``None`` would be identified as iterable (:issue:`43373`)
+- Fixed regression in :meth:`.Resampler.aggregate` when used after column selection would raise if ``func`` is a list of aggregation functions (:issue:`42905`)
 
 .. ---------------------------------------------------------------------------
 

pandas/core/resample.py

@@ -1043,6 +1043,7 @@ def __init__(self, obj, parent=None, groupby=None, **kwargs):
         # the resampler attributes
         for attr in self._attributes:
             setattr(self, attr, kwargs.get(attr, getattr(parent, attr)))
+        self._selection = kwargs.get("selection")
 
         self.binner = parent.binner
 

pandas/tests/resample/test_resampler_grouper.py

@@ -406,6 +406,21 @@ def test_resample_groupby_agg():
     tm.assert_frame_equal(result, expected)
 
 
+def test_resample_groupby_agg_listlike():
+    # GH 42905
+    ts = Timestamp("2021-02-28 00:00:00")
+    df = DataFrame({"class": ["beta"], "value": [69], "date": [ts]})
+    result = (
+        df.set_index("date")
+        .groupby("class")
+        .resample("M")["value"]
+        .agg(["sum", "size"])
+    )
+    index = pd.MultiIndex.from_tuples([("beta", ts)], names=["class", "date"])
+    expected = DataFrame([[69, 1]], index=index, columns=["sum", "size"])
+    tm.assert_frame_equal(result, expected)
+
+
 @pytest.mark.parametrize("keys", [["a"], ["a", "b"]])
 def test_empty(keys):
     # GH 26411