Don't sort columns for DataFrame init from list of Series (#14136)

closes #14132

This PR removes the re-sorting of dataframe columns when initialized by a series list.

Authors:
  - Matthew Roeschke (https://github.com/mroeschke)

Approvers:
  - GALI PREM SAGAR (https://github.com/galipremsagar)
  - Bradley Dice (https://github.com/bdice)

URL: #14136

python/cudf/cudf/core/dataframe.py

@@ -7885,9 +7885,7 @@ def _get_union_of_indices(indexes):
         return indexes[0]
     else:
         merged_index = cudf.core.index.GenericIndex._concat(indexes)
-        merged_index = merged_index.drop_duplicates()
-        inds = merged_index._values.argsort()
-        return merged_index.take(inds)
+        return merged_index.drop_duplicates()
 
 
 def _get_union_of_series_names(series_list):

python/cudf/cudf/tests/test_dataframe.py

@@ -221,6 +221,18 @@ def test_init_unaligned_with_index():
     assert_eq(pdf, gdf, check_dtype=False)
 
 
+def test_init_series_list_columns_unsort():
+    pseries = [
+        pd.Series(i, index=["b", "a", "c"], name=str(i)) for i in range(3)
+    ]
+    gseries = [
+        cudf.Series(i, index=["b", "a", "c"], name=str(i)) for i in range(3)
+    ]
+    pdf = pd.DataFrame(pseries)
+    gdf = cudf.DataFrame(gseries)
+    assert_eq(pdf, gdf)
+
+
 def test_series_basic():
     # Make series from buffer
     a1 = np.arange(10, dtype=np.float64)