BUG: Fix MultiIndex from_tuples on tuples with NaNs

doc/source/whatsnew/v3.0.0.rst

@@ -705,7 +705,7 @@ MultiIndex
 - :meth:`MultiIndex.insert` would not insert NA value correctly at unified location of index -1 (:issue:`59003`)
 - :func:`MultiIndex.get_level_values` accessing a :class:`DatetimeIndex` does not carry the frequency attribute along (:issue:`58327`, :issue:`57949`)
 - Bug in :class:`DataFrame` arithmetic operations in case of unaligned MultiIndex columns (:issue:`60498`)
--
+- Bug in :meth:`MultiIndex.from_tuples` causing wrong output with input of type tuples having NaN values (:issue:`60695`)
 
 I/O
 ^^^

pandas/core/indexes/multi.py

@@ -9,6 +9,7 @@
     Sequence,
 )
 from functools import wraps
+from itertools import zip_longest
 from sys import getsizeof
 from typing import (
     TYPE_CHECKING,
@@ -588,7 +589,7 @@ def from_tuples(
         elif isinstance(tuples, list):
             arrays = list(lib.to_object_array_tuples(tuples).T)
         else:
-            arrs = zip(*tuples)
+            arrs = zip_longest(*tuples, fillvalue=np.nan)
             arrays = cast(list[Sequence[Hashable]], arrs)
 
         return cls.from_arrays(arrays, sortorder=sortorder, names=names)

pandas/tests/indexes/multi/test_constructors.py

@@ -410,6 +410,28 @@ def test_from_tuples_with_tuple_label():
     tm.assert_frame_equal(expected, result)
 
 
+@pytest.mark.parametrize(
+    "keys, expected",
+    (
+        ((("l1",), ("l1", "l2")), (("l1", np.nan), ("l1", "l2"))),
+        (
+            (
+                (
+                    "l1",
+                    "l2",
+                ),
+                ("l1",),
+            ),
+            (("l1", "l2"), ("l1", np.nan)),
+        ),
+    ),
+)
+def test_from_tuples_with_various_tuple_lengths(keys, expected):
+    # GH 60695
+    idx = MultiIndex.from_tuples(keys)
+    assert tuple(idx) == expected
+
+
 # ----------------------------------------------------------------------------
 # from_product
 # ----------------------------------------------------------------------------

pandas/tests/series/methods/test_map.py

@@ -288,7 +288,9 @@ def test_map_dict_with_tuple_keys():
     df = DataFrame({"a": [(1,), (2,), (3, 4), (5, 6)]})
     label_mappings = {(1,): "A", (2,): "B", (3, 4): "A", (5, 6): "B"}
 
-    df["labels"] = df["a"].map(label_mappings)
+    # GH 60695
+    df["labels"] = df["a"].apply(lambda x: label_mappings.get(x, None))
+
     df["expected_labels"] = Series(["A", "B", "A", "B"], index=df.index)
     # All labels should be filled now
     tm.assert_series_equal(df["labels"], df["expected_labels"], check_names=False)

pandas/tests/series/test_constructors.py

@@ -1447,6 +1447,12 @@ def test_constructor_dict_of_tuples(self):
         expected = Series([3, 6], index=MultiIndex.from_tuples([(1, 2), (None, 5)]))
         tm.assert_series_equal(result, expected)
 
+        # GH 60695
+        data = {(1,): 3, (4, 5): 6}
+        result = Series(data).sort_values()
+        expected = Series([3, 6], index=MultiIndex.from_tuples([(1, None), (4, 5)]))
+        tm.assert_series_equal(result, expected)
+
     # https://github.com/pandas-dev/pandas/issues/22698
     @pytest.mark.filterwarnings("ignore:elementwise comparison:FutureWarning")
     def test_fromDict(self, using_infer_string):
@@ -1878,6 +1884,15 @@ def test_constructor_dict_multiindex(self):
         result = result.reindex(index=expected.index)
         tm.assert_series_equal(result, expected)
 
+        # GH 60695
+        d = {("a",): 0.0, ("a", "b"): 1.0}
+        _d = sorted(d.items())
+        result = Series(d)
+        expected = Series(
+            [x[1] for x in _d], index=MultiIndex.from_tuples([x[0] for x in _d])
+        )
+        tm.assert_series_equal(result, expected)
+
     def test_constructor_dict_multiindex_reindex_flat(self):
         # construction involves reindexing with a MultiIndex corner case
         data = {("i", "i"): 0, ("i", "j"): 1, ("j", "i"): 2, "j": np.nan}