🐛 Account for single-row to multi-row axis=0 apply (#23)

Author: ddelange

src/mapply/mapply.py

@@ -117,10 +117,10 @@ def run_apply(func, df_or_series, args=(), **kwargs):
     )
 
     if (
-        not isseries
-        and len(results) > 1
-        and results[0].index.equals(df_or_series.index)
+        isseries
+        or len(results) == 1
+        or len(results[0]) * len(results) in df_or_series.shape
     ):
-        return concat(results, axis=1, copy=False)
+        return concat(results, copy=False)
 
-    return concat(results, copy=False)
+    return concat(results, axis=1, copy=False)

tests/test_mapply.py

@@ -65,6 +65,13 @@ def test_df_mapply():
         df.mapply(sum, axis=1),
     )
 
+    # single row dataframe turns into multi row dataframe with same columns
+    mapply.init(progressbar=False, chunk_size=2, n_workers=2)
+    pd.testing.assert_frame_equal(
+        df.T.apply(lambda y: pd.Series(np.arange(10))),
+        df.T.mapply(lambda y: pd.Series(np.arange(10))),
+    )
+
 
 def test_series_mapply():
     # chunk_size>1