ARROW-1132: [Python] Unable to write pandas DataFrame w/MultiIndex containing duplicate values to parquet

python/pyarrow/table.pxi

@@ -320,12 +320,15 @@ cdef tuple _dataframe_to_arrays(
     cdef:
         list names = []
         list arrays = []
-        list index_levels = []
+        list index_columns = []
         DataType type = None
         dict metadata
+        Py_ssize_t i
+        Py_ssize_t n
 
     if preserve_index:
-        index_levels.extend(getattr(df.index, 'levels', [df.index]))
+        n = len(getattr(df.index, 'levels', [df.index]))
+        index_columns.extend(df.index.get_level_values(i) for i in range(n))
 
     for name in df.columns:
         col = df[name]
@@ -339,13 +342,13 @@ cdef tuple _dataframe_to_arrays(
         )
         names.append(name)
 
-    for i, level in enumerate(index_levels):
+    for i, column in enumerate(index_columns):
         arrays.append(
-            Array.from_pandas(level, timestamps_to_ms=timestamps_to_ms)
+            Array.from_pandas(column, timestamps_to_ms=timestamps_to_ms)
         )
-        names.append(pdcompat.index_level_name(level, i))
+        names.append(pdcompat.index_level_name(column, i))
 
-    metadata = pdcompat.construct_metadata(df, index_levels, preserve_index)
+    metadata = pdcompat.construct_metadata(df, index_columns, preserve_index)
     return names, arrays, metadata
 
 

python/pyarrow/tests/test_convert_pandas.py

@@ -640,3 +640,17 @@ def _check_series(s):
         _check_series(pd.Series([None] * 3, dtype=object))
         _check_series(pd.Series([np.nan] * 3, dtype=object))
         _check_series(pd.Series([np.sqrt(-1)] * 3, dtype=object))
+
+    def test_multiindex_duplicate_values(self):
+        num_rows = 3
+        numbers = list(range(num_rows))
+        index = pd.MultiIndex.from_arrays(
+            [['foo', 'foo', 'bar'], numbers],
+            names=['foobar', 'some_numbers'],
+        )
+
+        df = pd.DataFrame({'numbers': numbers}, index=index)
+
+        table = pa.Table.from_pandas(df)
+        result_df = table.to_pandas()
+        tm.assert_frame_equal(result_df, df)

python/pyarrow/tests/test_parquet.py

@@ -847,3 +847,24 @@ def read_multiple_files(paths, columns=None, nthreads=None, **kwargs):
 
     with pytest.raises(ValueError):
         read_multiple_files(mixed_paths)
+
+
+def test_multiindex_duplicate_values(tmpdir):
+    num_rows = 3
+    numbers = list(range(num_rows))
+    index = pd.MultiIndex.from_arrays(
+        [['foo', 'foo', 'bar'], numbers],
+        names=['foobar', 'some_numbers'],
+    )
+
+    df = pd.DataFrame({'numbers': numbers}, index=index)
+    table = pa.Table.from_pandas(df)
+
+    filename = tmpdir.join('dup_multi_index_levels.parquet').strpath
+
+    _write_table(table, filename)
+    result_table = _read_table(filename)
+    assert table.equals(result_table)
+
+    result_df = result_table.to_pandas()
+    tm.assert_frame_equal(result_df, df)