BUG: groupby shift fill_value, freq followup (#54133)

Author: mroeschke

doc/source/whatsnew/v2.1.0.rst

@@ -618,7 +618,7 @@ Other
 - Bug in :func:`assert_almost_equal` now throwing assertion error for two unequal sets (:issue:`51727`)
 - Bug in :func:`assert_frame_equal` checks category dtypes even when asked not to check index type (:issue:`52126`)
 - Bug in :meth:`DataFrame.reindex` with a ``fill_value`` that should be inferred with a :class:`ExtensionDtype` incorrectly inferring ``object`` dtype (:issue:`52586`)
-- Bug in :meth:`DataFrame.shift` and :meth:`Series.shift` when passing both "freq" and "fill_value" silently ignoring "fill_value" instead of raising ``ValueError`` (:issue:`53832`)
+- Bug in :meth:`DataFrame.shift` and :meth:`Series.shift` and :meth:`DataFrameGroupBy.shift` when passing both "freq" and "fill_value" silently ignoring "fill_value" instead of raising ``ValueError`` (:issue:`53832`)
 - Bug in :meth:`DataFrame.shift` with ``axis=1`` on a :class:`DataFrame` with a single :class:`ExtensionDtype` column giving incorrect results (:issue:`53832`)
 - Bug in :meth:`Series.align`, :meth:`DataFrame.align`, :meth:`Series.reindex`, :meth:`DataFrame.reindex`, :meth:`Series.interpolate`, :meth:`DataFrame.interpolate`, incorrectly failing to raise with method="asfreq" (:issue:`53620`)
 - Bug in :meth:`Series.map` when giving a callable to an empty series, the returned series had ``object`` dtype. It now keeps the original dtype (:issue:`52384`)

pandas/core/groupby/groupby.py

@@ -4911,7 +4911,7 @@ def shift(
         periods: int = 1,
         freq=None,
         axis: Axis | lib.NoDefault = lib.no_default,
-        fill_value=None,
+        fill_value=lib.no_default,
     ):
         """
         Shift each group by periods observations.
@@ -4934,6 +4934,9 @@ def shift(
         fill_value : optional
             The scalar value to use for newly introduced missing values.
 
+            .. versionchanged:: 2.1.0
+                Will raise a ``ValueError`` if ``freq`` is provided too.
+
         Returns
         -------
         Series or DataFrame
@@ -4991,6 +4994,8 @@ def shift(
             f = lambda x: x.shift(periods, freq, axis, fill_value)
             return self._python_apply_general(f, self._selected_obj, is_transform=True)
 
+        if fill_value is lib.no_default:
+            fill_value = None
         ids, _, ngroups = self.grouper.group_info
         res_indexer = np.zeros(len(ids), dtype=np.int64)
 

pandas/tests/groupby/test_groupby_shift_diff.py

@@ -7,6 +7,7 @@
     Series,
     Timedelta,
     Timestamp,
+    date_range,
 )
 import pandas._testing as tm
 
@@ -154,3 +155,21 @@ def test_multindex_empty_shift_with_fill():
     shifted_with_fill = df.groupby(["a", "b"]).shift(1, fill_value=0)
     tm.assert_frame_equal(shifted, shifted_with_fill)
     tm.assert_index_equal(shifted.index, shifted_with_fill.index)
+
+
+def test_shift_periods_freq():
+    # GH 54093
+    data = {"a": [1, 2, 3, 4, 5, 6], "b": [0, 0, 0, 1, 1, 1]}
+    df = DataFrame(data, index=date_range(start="20100101", periods=6))
+    result = df.groupby(df.index).shift(periods=-2, freq="D")
+    expected = DataFrame(data, index=date_range(start="2009-12-30", periods=6))
+    tm.assert_frame_equal(result, expected)
+
+
+def test_shift_disallow_freq_and_fill_value():
+    # GH 53832
+    data = {"a": [1, 2, 3, 4, 5, 6], "b": [0, 0, 0, 1, 1, 1]}
+    df = DataFrame(data, index=date_range(start="20100101", periods=6))
+    msg = "Cannot pass both 'freq' and 'fill_value' to (Series|DataFrame).shift"
+    with pytest.raises(ValueError, match=msg):
+        df.groupby(df.index).shift(periods=-2, freq="D", fill_value="1")