BUG: reindex using wrong fill value when indexing cols and index for uint dtypes (#48185)

Author: phofl

doc/source/whatsnew/v1.6.0.rst

@@ -151,7 +151,7 @@ Interval
 
 Indexing
 ^^^^^^^^
--
+- Bug in :meth:`DataFrame.reindex` filling with wrong values when indexing columns and index for ``uint`` dtypes (:issue:`48184`)
 -
 
 Missing

pandas/core/array_algos/take.py

@@ -546,9 +546,13 @@ def _take_2d_multi_object(
             out[:, col_mask] = fill_value
     for i in range(len(row_idx)):
         u_ = row_idx[i]
-        for j in range(len(col_idx)):
-            v = col_idx[j]
-            out[i, j] = arr[u_, v]
+
+        if u_ != -1:
+            for j in range(len(col_idx)):
+                v = col_idx[j]
+
+                if v != -1:
+                    out[i, j] = arr[u_, v]
 
 
 def _take_preprocess_indexer_and_fill_value(

pandas/tests/frame/methods/test_reindex.py

@@ -772,6 +772,16 @@ def test_reindex_fill_value(self):
         expected = df.reindex(range(15)).fillna(0)
         tm.assert_frame_equal(result, expected)
 
+    def test_reindex_uint_dtypes_fill_value(self, any_unsigned_int_numpy_dtype):
+        # GH#48184
+        df = DataFrame({"a": [1, 2], "b": [1, 2]}, dtype=any_unsigned_int_numpy_dtype)
+        result = df.reindex(columns=list("abcd"), index=[0, 1, 2, 3], fill_value=10)
+        expected = DataFrame(
+            {"a": [1, 2, 10, 10], "b": [1, 2, 10, 10], "c": 10, "d": 10},
+            dtype=any_unsigned_int_numpy_dtype,
+        )
+        tm.assert_frame_equal(result, expected)
+
     def test_reindex_dups(self):
 
         # GH4746, reindex on duplicate index error messages