Backport PR #42735: REGR: DataFrame.from_records with empty records #…

…42456 (#42740)

Co-authored-by: jbrockmendel <jbrockmendel@gmail.com>

doc/source/whatsnew/v1.3.2.rst

@@ -16,7 +16,7 @@ Fixed regressions
 ~~~~~~~~~~~~~~~~~
 - Performance regression in :meth:`DataFrame.isin` and :meth:`Series.isin` for nullable data types (:issue:`42714`)
 - Regression in updating values of :class:`pandas.Series` using boolean index, created by using :meth:`pandas.DataFrame.pop` (:issue:`42530`)
--
+- Regression in :meth:`DataFrame.from_records` with empty records (:issue:`42456`)
 -
 
 .. ---------------------------------------------------------------------------

pandas/core/internals/construction.py

@@ -761,6 +761,14 @@ def to_arrays(
                 # i.e. numpy structured array
                 columns = ensure_index(data.dtype.names)
                 arrays = [data[name] for name in columns]
+
+                if len(data) == 0:
+                    # GH#42456 the indexing above results in list of 2D ndarrays
+                    # TODO: is that an issue with numpy?
+                    for i, arr in enumerate(arrays):
+                        if arr.ndim == 2:
+                            arrays[i] = arr[:, 0]
+
                 return arrays, columns
         return [], ensure_index([])
 

pandas/tests/frame/constructors/test_from_records.py

@@ -457,3 +457,16 @@ def test_from_records_empty_with_nonempty_fields_gh3682(self):
         b = a[:0]
         df2 = DataFrame.from_records(b, index="id")
         tm.assert_frame_equal(df2, df.iloc[:0])
+
+    def test_from_records_empty2(self):
+        # GH#42456
+        dtype = [("prop", int)]
+        shape = (0, len(dtype))
+        arr = np.empty(shape, dtype=dtype)
+
+        result = DataFrame.from_records(arr)
+        expected = DataFrame({"prop": np.array([], dtype=int)})
+        tm.assert_frame_equal(result, expected)
+
+        alt = DataFrame(arr)
+        tm.assert_frame_equal(alt, expected)