ENH: Fix output of assert_frame_equal if indexes differ and check_like=True

doc/source/whatsnew/v1.2.0.rst

@@ -228,6 +228,7 @@ Other enhancements
 - :class:`Rolling` now supports the ``closed`` argument for fixed windows (:issue:`34315`)
 - :class:`DatetimeIndex` and :class:`Series` with ``datetime64`` or ``datetime64tz`` dtypes now support ``std`` (:issue:`37436`)
 - :class:`Window` now supports all Scipy window types in ``win_type`` with flexible keyword argument support (:issue:`34556`)
+- :meth:`testing.assert_index_equal` now has a ``check_order`` parameter that allows indexes to be checked in an order-insensitive manner (:issue:`37478`)
 
 .. _whatsnew_120.api_breaking.python:
 

pandas/_testing.py

@@ -667,6 +667,7 @@ def assert_index_equal(
     check_less_precise: Union[bool, int] = no_default,
     check_exact: bool = True,
     check_categorical: bool = True,
+    check_order: bool = True,
     rtol: float = 1.0e-5,
     atol: float = 1.0e-8,
     obj: str = "Index",
@@ -696,6 +697,12 @@ def assert_index_equal(
         Whether to compare number exactly.
     check_categorical : bool, default True
         Whether to compare internal Categorical exactly.
+    check_order : bool, default True
+        Whether to compare the order of index entries as well as their values.
+        If True, both indexes must contain the same elements, in the same order.
+        If False, both indexes must contain the same elements, but in any order.
+
+        .. versionadded:: 1.2.0
     rtol : float, default 1e-5
         Relative tolerance. Only used when check_exact is False.
 
@@ -762,6 +769,11 @@ def _get_ilevel_values(index, level):
         msg3 = f"{len(right)}, {right}"
         raise_assert_detail(obj, msg1, msg2, msg3)
 
+    # If order doesn't matter then sort the index entries
+    if not check_order:
+        left = left.sort_values()
+        right = right.sort_values()
+
     # MultiIndex special comparison for little-friendly error messages
     if left.nlevels > 1:
         left = cast(MultiIndex, left)
@@ -1582,9 +1594,6 @@ def assert_frame_equal(
             obj, f"{obj} shape mismatch", f"{repr(left.shape)}", f"{repr(right.shape)}"
         )
 
-    if check_like:
-        left, right = left.reindex_like(right), right
-
     if check_flags:
         assert left.flags == right.flags, f"{repr(left.flags)} != {repr(right.flags)}"
 
@@ -1596,6 +1605,7 @@ def assert_frame_equal(
         check_names=check_names,
         check_exact=check_exact,
         check_categorical=check_categorical,
+        check_order=not check_like,
         rtol=rtol,
         atol=atol,
         obj=f"{obj}.index",
@@ -1609,11 +1619,15 @@ def assert_frame_equal(
         check_names=check_names,
         check_exact=check_exact,
         check_categorical=check_categorical,
+        check_order=not check_like,
         rtol=rtol,
         atol=atol,
         obj=f"{obj}.columns",
     )
 
+    if check_like:
+        left, right = left.reindex_like(right), right
+
     # compare by blocks
     if by_blocks:
         rblocks = right._to_dict_of_blocks()

pandas/tests/util/test_assert_frame_equal.py

@@ -145,7 +145,8 @@ def test_empty_dtypes(check_dtype):
         tm.assert_frame_equal(df1, df2, **kwargs)
 
 
-def test_frame_equal_index_mismatch(obj_fixture):
+@pytest.mark.parametrize("check_like", [True, False])
+def test_frame_equal_index_mismatch(check_like, obj_fixture):
     msg = f"""{obj_fixture}\\.index are different
 
 {obj_fixture}\\.index values are different \\(33\\.33333 %\\)
@@ -156,10 +157,11 @@ def test_frame_equal_index_mismatch(obj_fixture):
     df2 = DataFrame({"A": [1, 2, 3], "B": [4, 5, 6]}, index=["a", "b", "d"])
 
     with pytest.raises(AssertionError, match=msg):
-        tm.assert_frame_equal(df1, df2, obj=obj_fixture)
+        tm.assert_frame_equal(df1, df2, check_like=check_like, obj=obj_fixture)
 
 
-def test_frame_equal_columns_mismatch(obj_fixture):
+@pytest.mark.parametrize("check_like", [True, False])
+def test_frame_equal_columns_mismatch(check_like, obj_fixture):
     msg = f"""{obj_fixture}\\.columns are different
 
 {obj_fixture}\\.columns values are different \\(50\\.0 %\\)
@@ -170,7 +172,7 @@ def test_frame_equal_columns_mismatch(obj_fixture):
     df2 = DataFrame({"A": [1, 2, 3], "b": [4, 5, 6]}, index=["a", "b", "c"])
 
     with pytest.raises(AssertionError, match=msg):
-        tm.assert_frame_equal(df1, df2, obj=obj_fixture)
+        tm.assert_frame_equal(df1, df2, check_like=check_like, obj=obj_fixture)
 
 
 def test_frame_equal_block_mismatch(by_blocks_fixture, obj_fixture):

pandas/tests/util/test_assert_index_equal.py

@@ -115,6 +115,28 @@ def test_index_equal_values_too_far(check_exact, rtol):
         tm.assert_index_equal(idx1, idx2, **kwargs)
 
 
+@pytest.mark.parametrize("check_order", [True, False])
+def test_index_equal_value_oder_mismatch(check_exact, rtol, check_order):
+    idx1 = Index([1, 2, 3])
+    idx2 = Index([3, 2, 1])
+
+    msg = """Index are different
+
+Index values are different \\(66\\.66667 %\\)
+\\[left\\]:  Int64Index\\(\\[1, 2, 3\\], dtype='int64'\\)
+\\[right\\]: Int64Index\\(\\[3, 2, 1\\], dtype='int64'\\)"""
+
+    if check_order:
+        with pytest.raises(AssertionError, match=msg):
+            tm.assert_index_equal(
+                idx1, idx2, check_exact=check_exact, rtol=rtol, check_order=True
+            )
+    else:
+        tm.assert_index_equal(
+            idx1, idx2, check_exact=check_exact, rtol=rtol, check_order=False
+        )
+
+
 def test_index_equal_level_values_mismatch(check_exact, rtol):
     idx1 = MultiIndex.from_tuples([("A", 2), ("A", 2), ("B", 3), ("B", 4)])
     idx2 = MultiIndex.from_tuples([("A", 1), ("A", 2), ("B", 3), ("B", 4)])