BUG: cast to correct dtype in Index.drop()

closes #18304

Author: toobaz

doc/source/whatsnew/v0.22.0.txt

@@ -103,6 +103,7 @@ Indexing
 
 - Bug in :func:`Series.truncate` which raises ``TypeError`` with a monotonic ``PeriodIndex`` (:issue:`17717`)
 - Bug in :func:`DataFrame.groupby` where tuples were interpreted as lists of keys rather than as keys (:issue:`17979`, :issue:`18249`)
+- Bug in :func:`Index.drop` when passing a list of both tuples and non-tuples (:issue:`18304`)
 -
 -
 

pandas/core/common.py

@@ -404,7 +404,7 @@ def _asarray_tuplesafe(values, dtype=None):
     return result
 
 
-def _index_labels_to_array(labels):
+def _index_labels_to_array(labels, dtype=None):
     if isinstance(labels, (compat.string_types, tuple)):
         labels = [labels]
 
@@ -414,7 +414,7 @@ def _index_labels_to_array(labels):
         except TypeError:  # non-iterable
             labels = [labels]
 
-    labels = _asarray_tuplesafe(labels)
+    labels = _asarray_tuplesafe(labels, dtype=dtype)
 
     return labels
 

pandas/core/indexes/base.py

@@ -3747,7 +3747,8 @@ def drop(self, labels, errors='raise'):
         -------
         dropped : Index
         """
-        labels = _index_labels_to_array(labels)
+        arr_dtype = 'object' if self.dtype == 'object' else None
+        labels = _index_labels_to_array(labels, dtype=arr_dtype)
         indexer = self.get_indexer(labels)
         mask = indexer == -1
         if mask.any():

pandas/tests/indexes/test_base.py

@@ -1341,6 +1341,27 @@ def test_drop(self):
         expected = Index([1, 2])
         tm.assert_index_equal(dropped, expected)
 
+    @pytest.mark.parametrize("values", [['a', 'b', ('c', 'd')],
+                                        ['a', ('c', 'd'), 'b'],
+                                        [('c', 'd'), 'a', 'b']])
+    @pytest.mark.parametrize("to_drop", [[('c', 'd'), 'a'], ['a', ('c', 'd')]])
+    def test_drop_tuple(self, values, to_drop):
+        # GH 18304
+        index = pd.Index(values)
+        expected = pd.Index(['b'])
+
+        result = index.drop(to_drop)
+        tm.assert_index_equal(result, expected)
+
+        removed = index.drop(to_drop[0])
+        for drop_me in to_drop[1], [to_drop[1]]:
+            result = removed.drop(drop_me)
+            tm.assert_index_equal(result, expected)
+
+        removed = index.drop(to_drop[1])
+        for drop_me in to_drop[1], [to_drop[1]]:
+            pytest.raises(ValueError, removed.drop, drop_me)
+
     def test_tuple_union_bug(self):
         import pandas
         import numpy as np