Backport PR pandas-dev#57058: BUG: Series.pct_change with empty Series

meeseeksmachine · Jan 24, 2024 · ba44ed5 · ba44ed5
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diff --git a/doc/source/whatsnew/v2.2.1.rst b/doc/source/whatsnew/v2.2.1.rst
@@ -14,6 +14,7 @@ including other versions of pandas.
 Fixed regressions
 ~~~~~~~~~~~~~~~~~
 - Fixed regression in :func:`merge_ordered` raising ``TypeError`` for ``fill_method="ffill"`` and ``how="left"`` (:issue:`57010`)
+- Fixed regression in :meth:`Series.pct_change` raising a ``ValueError`` for an empty :class:`Series` (:issue:`57056`)
 
 .. ---------------------------------------------------------------------------
 .. _whatsnew_221.bug_fixes:

diff --git a/pandas/core/generic.py b/pandas/core/generic.py
@@ -12126,19 +12126,20 @@ def pct_change(
             if limit is lib.no_default:
                 cols = self.items() if self.ndim == 2 else [(None, self)]
                 for _, col in cols:
-                    mask = col.isna().values
-                    mask = mask[np.argmax(~mask) :]
-                    if mask.any():
-                        warnings.warn(
-                            "The default fill_method='pad' in "
-                            f"{type(self).__name__}.pct_change is deprecated and will "
-                            "be removed in a future version. Either fill in any "
-                            "non-leading NA values prior to calling pct_change or "
-                            "specify 'fill_method=None' to not fill NA values.",
-                            FutureWarning,
-                            stacklevel=find_stack_level(),
-                        )
-                        break
+                    if len(col) > 0:
+                        mask = col.isna().values
+                        mask = mask[np.argmax(~mask) :]
+                        if mask.any():
+                            warnings.warn(
+                                "The default fill_method='pad' in "
+                                f"{type(self).__name__}.pct_change is deprecated and "
+                                "will be removed in a future version. Either fill in "
+                                "any non-leading NA values prior to calling pct_change "
+                                "or specify 'fill_method=None' to not fill NA values.",
+                                FutureWarning,
+                                stacklevel=find_stack_level(),
+                            )
+                            break
             fill_method = "pad"
         if limit is lib.no_default:
             limit = None

diff --git a/pandas/tests/series/methods/test_pct_change.py b/pandas/tests/series/methods/test_pct_change.py
@@ -118,3 +118,11 @@ def test_pct_change_no_warning_na_beginning():
     result = ser.pct_change()
     expected = Series([np.nan, np.nan, np.nan, 1, 0.5])
     tm.assert_series_equal(result, expected)
+
+
+def test_pct_change_empty():
+    # GH 57056
+    ser = Series([], dtype="float64")
+    expected = ser.copy()
+    result = ser.pct_change(periods=0)
+    tm.assert_series_equal(expected, result)