BUG: add reset logic for Grouper if new obj is passed in (#26564)

pandas/core/groupby/grouper.py

@@ -107,7 +107,6 @@ def __init__(self, key=None, level=None, freq=None, axis=0, sort=False):
         self.freq = freq
         self.axis = axis
         self.sort = sort
-
         self.grouper = None
         self.obj = None
         self.indexer = None

pandas/tests/resample/test_resampler_grouper.py

@@ -1,6 +1,7 @@
 from textwrap import dedent
 
 import numpy as np
+import pytest
 
 from pandas.util._test_decorators import async_mark
 
@@ -295,3 +296,35 @@ def test_median_duplicate_columns():
     result = df.resample("5s").median()
     expected.columns = result.columns
     tm.assert_frame_equal(result, expected)
+
+
+@pytest.mark.xfail(reason="marked as xfail for: #26564")
+def test_same_grouper_on_different_frames():
+
+    df1 = pd.DataFrame(
+        [["a", 1, 2], ["a", 4, 5], ["b", 2, 3]], columns=["type", "num1", "num2"],
+    )
+    df1["date"] = pd.to_datetime(["05/29/2019", "05/28/2019", "05/27/2019"])
+
+    df2 = pd.DataFrame([["c", 6, 7], ["d", 8, 9]], columns=["type", "num1", "num2"],)
+    df2["date"] = pd.to_datetime(["02/12/2018", "03/13/2018"])
+
+    groupbys = ["type", pd.Grouper(key="date", freq="1D")]
+
+    df1.groupby(groupbys).sum()
+    result = df2.groupby(groupbys).count()
+
+    expected = pd.DataFrame(
+        {
+            "num1": {
+                ("c", Timestamp("2018-02-12 00:00:00", freq="D")): 1,
+                ("d", Timestamp("2018-03-13 00:00:00", freq="D")): 1,
+            },
+            "num2": {
+                ("c", Timestamp("2018-02-12 00:00:00", freq="D")): 1,
+                ("d", Timestamp("2018-03-13 00:00:00", freq="D")): 1,
+            },
+        }
+    )
+    expected.index.set_names(["type", "date"], inplace=True)
+    tm.assert_frame_equal(result, expected)