fix bug #GH23020

Author: makbigc

doc/source/whatsnew/v0.24.0.txt

@@ -1360,6 +1360,12 @@ Sparse
 - Bug in unary inversion operator (``~``) on a ``SparseSeries`` with boolean values. The performance of this has also been improved (:issue:`22835`)
 - Bug in :meth:`SparseArary.unique` not returning the unique values (:issue:`19595`)
 
+IntegerArray
+^^^^^^^^^^^^
+
+- Bug in :func:`pandas.merge` when merging on an Integer extension array (:issue:`23020`)
+
+
 Build Changes
 ^^^^^^^^^^^^^
 

pandas/core/reshape/merge.py

@@ -8,10 +8,43 @@
 
 import numpy as np
 
+<<<<<<< HEAD
 from pandas._libs import hashtable as libhashtable, join as libjoin, lib
 import pandas.compat as compat
 from pandas.compat import filter, lzip, map, range, zip
 from pandas.errors import MergeError
+=======
+from pandas import (Categorical, DataFrame,
+                    Index, MultiIndex, Timedelta, Series)
+from pandas.core.arrays.categorical import _recode_for_categories
+from pandas.core.frame import _merge_doc
+from pandas.core.dtypes.common import (
+    is_datetime64tz_dtype,
+    is_datetime64_dtype,
+    needs_i8_conversion,
+    is_int64_dtype,
+    is_array_like,
+    is_categorical_dtype,
+    is_integer_dtype,
+    is_float_dtype,
+    is_number,
+    is_numeric_dtype,
+    is_integer,
+    is_extension_array_dtype,
+    is_int_or_datetime_dtype,
+    is_dtype_equal,
+    is_bool,
+    is_bool_dtype,
+    is_list_like,
+    is_datetimelike,
+    ensure_int64,
+    ensure_float64,
+    ensure_object,
+    _get_dtype)
+from pandas.core.dtypes.missing import na_value_for_dtype
+from pandas.core.internals import (items_overlap_with_suffix,
+                                   concatenate_block_managers)
+>>>>>>> fix bug #GH23020
 from pandas.util._decorators import Appender, Substitution
 
 from pandas.core.dtypes.common import (
@@ -1518,6 +1551,10 @@ def _factorize_keys(lk, rk, sort=True):
 
         lk = ensure_int64(lk.codes)
         rk = ensure_int64(rk)
+    elif is_extension_array_dtype(lk) and is_extension_array_dtype(rk):
+        klass = libhashtable.Factorizer
+        lk = ensure_object(lk)
+        rk = ensure_object(rk)
     elif is_int_or_datetime_dtype(lk) and is_int_or_datetime_dtype(rk):
         klass = libhashtable.Int64Factorizer
         lk = ensure_int64(com.values_from_object(lk))

pandas/tests/reshape/merge/test_merge.py

@@ -1842,6 +1842,16 @@ def test_merging_with_bool_or_int_cateorical_column(self, category_column,
             CDT(categories, ordered=ordered))
         assert_frame_equal(expected, result)
 
+    def test_merge_on_int_array(self):
+        # GH  23020
+        df = pd.DataFrame({'A': pd.Series([1, 2, np.nan], dtype='Int64'),
+                           'B': 1})
+        result = pd.merge(df, df, on='A')
+        expected = pd.DataFrame({'A': pd.Series([1, 2, np.nan], dtype='Int64'),
+                                 'B_x': 1,
+                                 'B_y': 1})
+        assert_frame_equal(result, expected, check_dtype=True)
+
 
 @pytest.fixture
 def left_df():