[SPARK-25351][SQL][Python] Handle Pandas category type when converting from Python with Arrow

python/pyspark/sql/pandas/serializers.py

@@ -154,6 +154,9 @@ def create_array(s, t):
             # Ensure timestamp series are in expected form for Spark internal representation
             if t is not None and pa.types.is_timestamp(t):
                 s = _check_series_convert_timestamps_internal(s, self._timezone)
+            elif type(s.dtype) == pd.CategoricalDtype:
+                # Note: This can be removed once minimum pyarrow version is >= 0.16.1
+                s = s.astype(s.dtypes.categories.dtype)
             try:
                 array = pa.Array.from_pandas(s, mask=mask, type=t, safe=self._safecheck)
             except pa.ArrowException as e:

python/pyspark/sql/pandas/types.py

@@ -114,6 +114,8 @@ def from_arrow_type(at):
         return StructType(
             [StructField(field.name, from_arrow_type(field.type), nullable=field.nullable)
              for field in at])
+    elif types.is_dictionary(at):
+        spark_type = from_arrow_type(at.value_type)
     else:
         raise TypeError("Unsupported type in conversion from Arrow: " + str(at))
     return spark_type

python/pyspark/sql/tests/test_arrow.py

@@ -415,6 +415,32 @@ def run_test(num_records, num_parts, max_records, use_delay=False):
         for case in cases:
             run_test(*case)
 
+    def test_createDateFrame_with_category_type(self):
+        pdf = pd.DataFrame({"A": [u"a", u"b", u"c", u"a"]})
+        pdf["B"] = pdf["A"].astype('category')
+        category_first_element = dict(enumerate(pdf['B'].cat.categories))[0]
+
+        with self.sql_conf({"spark.sql.execution.arrow.pyspark.enabled": True}):
+            arrow_df = self.spark.createDataFrame(pdf)
+            arrow_type = arrow_df.dtypes[1][1]
+            result_arrow = arrow_df.toPandas()
+            arrow_first_category_element = result_arrow["B"][0]
+
+        with self.sql_conf({"spark.sql.execution.arrow.pyspark.enabled": False}):
+            df = self.spark.createDataFrame(pdf)
+            spark_type = df.dtypes[1][1]
+            result_spark = df.toPandas()
+            spark_first_category_element = result_spark["B"][0]
+
+        assert_frame_equal(result_spark, result_arrow)
+
+        # ensure original category elements are string
+        assert isinstance(category_first_element, str)
+        # spark data frame and arrow execution mode enabled data frame type must match pandas
+        assert spark_type == arrow_type == 'string'
+        assert isinstance(arrow_first_category_element, str)
+        assert isinstance(spark_first_category_element, str)
+
 
 @unittest.skipIf(
     not have_pandas or not have_pyarrow,

python/pyspark/sql/tests/test_pandas_udf_scalar.py

@@ -897,6 +897,27 @@ def test_timestamp_dst(self):
             result = df.withColumn('time', foo_udf(df.time))
             self.assertEquals(df.collect(), result.collect())
 
+    def test_udf_category_type(self):
+
+        @pandas_udf('string')
+        def to_category_func(x):
+            return x.astype('category')
+
+        pdf = pd.DataFrame({"A": [u"a", u"b", u"c", u"a"]})
+        df = self.spark.createDataFrame(pdf)
+        df = df.withColumn("B", to_category_func(df['A']))
+        result_spark = df.toPandas()
+
+        spark_type = df.dtypes[1][1]
+        # spark data frame and arrow execution mode enabled data frame type must match pandas
+        assert spark_type == 'string'
+
+        # Check result value of column 'B' must be equal to column 'A'
+        for i in range(0, len(result_spark["A"])):
+            assert result_spark["A"][i] == result_spark["B"][i]
+            assert isinstance(result_spark["A"][i], str)
+            assert isinstance(result_spark["B"][i], str)
+
     @unittest.skipIf(sys.version_info[:2] < (3, 5), "Type hints are supported from Python 3.5.")
     def test_type_annotation(self):
         # Regression test to check if type hints can be used. See SPARK-23569.