[SPARK-24324][PYTHON] Pandas Grouped Map UDF should assign result columns by name

docs/sql-programming-guide.md

@@ -1752,14 +1752,10 @@ To use `groupBy().apply()`, the user needs to define the following:
 * A Python function that defines the computation for each group.
 * A `StructType` object or a string that defines the schema of the output `DataFrame`.
 
-The output schema will be applied to the columns of the returned `pandas.DataFrame` in order by position,
-not by name. This means that the columns in the `pandas.DataFrame` must be indexed so that their
-position matches the corresponding field in the schema.
-
-Note that when creating a new `pandas.DataFrame` using a dictionary, the actual position of the column
-can differ from the order that it was placed in the dictionary. It is recommended in this case to
-explicitly define the column order using the `columns` keyword, e.g.
-`pandas.DataFrame({'id': ids, 'a': data}, columns=['id', 'a'])`, or alternatively use an `OrderedDict`.
+The column labels of the returned `pandas.DataFrame` must either match the field names in the
+defined output schema if specified as strings, or match the field data types by position if not
+strings, e.g. integer indices. See [pandas.DataFrame](https://pandas.pydata.org/pandas-docs/stable/generated/pandas.DataFrame.html#pandas.DataFrame)
+on how to label columns when constructing a `pandas.DataFrame`.
 
 Note that all data for a group will be loaded into memory before the function is applied. This can
 lead to out of memory exceptons, especially if the group sizes are skewed. The configuration for

python/pyspark/sql/functions.py

@@ -2550,9 +2550,10 @@ def pandas_udf(f=None, returnType=None, functionType=None):
 
        A grouped map UDF defines transformation: A `pandas.DataFrame` -> A `pandas.DataFrame`
        The returnType should be a :class:`StructType` describing the schema of the returned
-       `pandas.DataFrame`.
-       The length of the returned `pandas.DataFrame` can be arbitrary and the columns must be
-       indexed so that their position matches the corresponding field in the schema.
+       `pandas.DataFrame`. The column labels of the returned `pandas.DataFrame` must either match
+       the field names in the defined returnType schema if specified as strings, or match the
+       field data types by position if not strings, e.g. integer indices.
+       The length of the returned `pandas.DataFrame` can be arbitrary.
 
        Grouped map UDFs are used with :meth:`pyspark.sql.GroupedData.apply`.
 

python/pyspark/sql/tests.py

@@ -4449,7 +4449,6 @@ def test_vectorized_udf_chained(self):
 
     def test_vectorized_udf_wrong_return_type(self):
         from pyspark.sql.functions import pandas_udf, col
-        df = self.spark.range(10)
         with QuietTest(self.sc):
             with self.assertRaisesRegexp(
                     NotImplementedError,
@@ -5034,6 +5033,109 @@ def foo3(key, pdf):
         expected4 = udf3.func((), pdf)
         self.assertPandasEqual(expected4, result4)
 
+    def test_column_order(self):
+        from collections import OrderedDict
+        import pandas as pd
+        from pyspark.sql.functions import pandas_udf, PandasUDFType
+
+        # Helper function to set column names from a list
+        def rename_pdf(pdf, names):
+            pdf.rename(columns={old: new for old, new in
+                                zip(pd_result.columns, names)}, inplace=True)
+
+        df = self.data
+        grouped_df = df.groupby('id')
+        grouped_pdf = df.toPandas().groupby('id')
+
+        # Function returns a pdf with required column names, but order could be arbitrary using dict
+        def change_col_order(pdf):
+            # Constructing a DataFrame from a dict should result in the same order,
+            # but use from_items to ensure the pdf column order is different than schema
+            return pd.DataFrame.from_items([
+                ('id', pdf.id),
+                ('u', pdf.v * 2),
+                ('v', pdf.v)])
+
+        ordered_udf = pandas_udf(
+            change_col_order,
+            'id long, v int, u int',
+            PandasUDFType.GROUPED_MAP
+        )
+
+        # The UDF result should assign columns by name from the pdf
+        result = grouped_df.apply(ordered_udf).sort('id', 'v')\
+            .select('id', 'u', 'v').toPandas()
+        pd_result = grouped_pdf.apply(change_col_order)
+        expected = pd_result.sort_values(['id', 'v']).reset_index(drop=True)
+        self.assertPandasEqual(expected, result)
+
+        # Function returns a pdf with positional columns, indexed by range
+        def range_col_order(pdf):
+            # Create a DataFrame with positional columns, fix types to long
+            return pd.DataFrame(list(zip(pdf.id, pdf.v * 3, pdf.v)), dtype='int64')
+
+        range_udf = pandas_udf(
+            range_col_order,
+            'id long, u long, v long',
+            PandasUDFType.GROUPED_MAP
+        )
+
+        # The UDF result uses positional columns from the pdf
+        result = grouped_df.apply(range_udf).sort('id', 'v') \
+            .select('id', 'u', 'v').toPandas()
+        pd_result = grouped_pdf.apply(range_col_order)
+        rename_pdf(pd_result, ['id', 'u', 'v'])
+        expected = pd_result.sort_values(['id', 'v']).reset_index(drop=True)
+        self.assertPandasEqual(expected, result)
+
+        # Function returns a pdf with columns indexed with integers
+        def int_index(pdf):
+            return pd.DataFrame(OrderedDict([(0, pdf.id), (1, pdf.v * 4), (2, pdf.v)]))
+
+        int_index_udf = pandas_udf(
+            int_index,
+            'id long, u int, v int',
+            PandasUDFType.GROUPED_MAP
+        )
+
+        # The UDF result should assign columns by position of integer index
+        result = grouped_df.apply(int_index_udf).sort('id', 'v') \
+            .select('id', 'u', 'v').toPandas()
+        pd_result = grouped_pdf.apply(int_index)
+        rename_pdf(pd_result, ['id', 'u', 'v'])
+        expected = pd_result.sort_values(['id', 'v']).reset_index(drop=True)
+        self.assertPandasEqual(expected, result)
+
+        @pandas_udf('id long, v int', PandasUDFType.GROUPED_MAP)
+        def column_name_typo(pdf):
+            return pd.DataFrame({'iid': pdf.id, 'v': pdf.v})
+
+        @pandas_udf('id long, v int', PandasUDFType.GROUPED_MAP)
+        def invalid_positional_types(pdf):
+            return pd.DataFrame([(u'a', 1.2)])
+
+        with QuietTest(self.sc):
+            with self.assertRaisesRegexp(Exception, "KeyError: 'id'"):
+                grouped_df.apply(column_name_typo).collect()
+            with self.assertRaisesRegexp(Exception, "No cast implemented"):
+                grouped_df.apply(invalid_positional_types).collect()
+
+    def test_positional_assignment_conf(self):
+        import pandas as pd
+        from pyspark.sql.functions import pandas_udf, PandasUDFType
+
+        with self.sql_conf({"spark.sql.execution.pandas.groupedMap.assignColumnsByPosition": True}):
+
+            @pandas_udf("a string, b float", PandasUDFType.GROUPED_MAP)
+            def foo(_):
+                return pd.DataFrame([('hi', 1)], columns=['x', 'y'])
+
+            df = self.data
+            result = df.groupBy('id').apply(foo).select('a', 'b').collect()
+            for r in result:
+                self.assertEqual(r.a, 'hi')
+                self.assertEqual(r.b, 1)
+
 
 @unittest.skipIf(
     not _have_pandas or not _have_pyarrow,

python/pyspark/worker.py

@@ -38,6 +38,9 @@
 from pyspark.util import _get_argspec, fail_on_stopiteration
 from pyspark import shuffle
 
+if sys.version >= '3':
+    basestring = str
+
 pickleSer = PickleSerializer()
 utf8_deserializer = UTF8Deserializer()
 
@@ -92,7 +95,10 @@ def verify_result_length(*a):
     return lambda *a: (verify_result_length(*a), arrow_return_type)
 
 
-def wrap_grouped_map_pandas_udf(f, return_type, argspec):
+def wrap_grouped_map_pandas_udf(f, return_type, argspec, runner_conf):
+    assign_cols_by_pos = runner_conf.get(
+        "spark.sql.execution.pandas.groupedMap.assignColumnsByPosition", False)
+
     def wrapped(key_series, value_series):
         import pandas as pd
 
@@ -110,9 +116,20 @@ def wrapped(key_series, value_series):
                 "Number of columns of the returned pandas.DataFrame "
                 "doesn't match specified schema. "
                 "Expected: {} Actual: {}".format(len(return_type), len(result.columns)))
-        arrow_return_types = (to_arrow_type(field.dataType) for field in return_type)
-        return [(result[result.columns[i]], arrow_type)
-                for i, arrow_type in enumerate(arrow_return_types)]
+
+        if not assign_cols_by_pos:
+            try:
+                # Assign result columns by schema name
+                return [(result[field.name], to_arrow_type(field.dataType))
+                        for field in return_type]
+            except KeyError:
+                # Raise error if columns are labeled with strings, else allow positional assignment
+                if any(isinstance(name, basestring) for name in result.columns):
+                    raise
+
+        # Assign result columns by position
+        return [(result[result.columns[i]], to_arrow_type(field.dataType))
+                for i, field in enumerate(return_type)]
 
     return wrapped
 
@@ -143,7 +160,7 @@ def wrapped(*series):
     return lambda *a: (wrapped(*a), arrow_return_type)
 
 
-def read_single_udf(pickleSer, infile, eval_type):
+def read_single_udf(pickleSer, infile, eval_type, runner_conf):
     num_arg = read_int(infile)
     arg_offsets = [read_int(infile) for i in range(num_arg)]
     row_func = None
@@ -163,7 +180,7 @@ def read_single_udf(pickleSer, infile, eval_type):
         return arg_offsets, wrap_scalar_pandas_udf(func, return_type)
     elif eval_type == PythonEvalType.SQL_GROUPED_MAP_PANDAS_UDF:
         argspec = _get_argspec(row_func)  # signature was lost when wrapping it
-        return arg_offsets, wrap_grouped_map_pandas_udf(func, return_type, argspec)
+        return arg_offsets, wrap_grouped_map_pandas_udf(func, return_type, argspec, runner_conf)
     elif eval_type == PythonEvalType.SQL_GROUPED_AGG_PANDAS_UDF:
         return arg_offsets, wrap_grouped_agg_pandas_udf(func, return_type)
     elif eval_type == PythonEvalType.SQL_WINDOW_AGG_PANDAS_UDF:
@@ -175,6 +192,26 @@ def read_single_udf(pickleSer, infile, eval_type):
 
 
 def read_udfs(pickleSer, infile, eval_type):
+    runner_conf = {}
+
+    if eval_type in (PythonEvalType.SQL_SCALAR_PANDAS_UDF,
+                     PythonEvalType.SQL_GROUPED_MAP_PANDAS_UDF,
+                     PythonEvalType.SQL_GROUPED_AGG_PANDAS_UDF,
+                     PythonEvalType.SQL_WINDOW_AGG_PANDAS_UDF):
+
+        # Load conf used for pandas_udf evaluation
+        num_conf = read_int(infile)
+        for i in range(num_conf):
+            k = utf8_deserializer.loads(infile)
+            v = utf8_deserializer.loads(infile)
+            runner_conf[k] = v
+
+        # NOTE: if timezone is set here, that implies respectSessionTimeZone is True
+        timezone = runner_conf.get("spark.sql.session.timeZone", None)
+        ser = ArrowStreamPandasSerializer(timezone)
+    else:
+        ser = BatchedSerializer(PickleSerializer(), 100)
+
     num_udfs = read_int(infile)
     udfs = {}
     call_udf = []
@@ -189,7 +226,7 @@ def read_udfs(pickleSer, infile, eval_type):
 
         # See FlatMapGroupsInPandasExec for how arg_offsets are used to
         # distinguish between grouping attributes and data attributes
-        arg_offsets, udf = read_single_udf(pickleSer, infile, eval_type)
+        arg_offsets, udf = read_single_udf(pickleSer, infile, eval_type, runner_conf)
         udfs['f'] = udf
         split_offset = arg_offsets[0] + 1
         arg0 = ["a[%d]" % o for o in arg_offsets[1: split_offset]]
@@ -201,7 +238,7 @@ def read_udfs(pickleSer, infile, eval_type):
         # In the special case of a single UDF this will return a single result rather
         # than a tuple of results; this is the format that the JVM side expects.
         for i in range(num_udfs):
-            arg_offsets, udf = read_single_udf(pickleSer, infile, eval_type)
+            arg_offsets, udf = read_single_udf(pickleSer, infile, eval_type, runner_conf)
             udfs['f%d' % i] = udf
             args = ["a[%d]" % o for o in arg_offsets]
             call_udf.append("f%d(%s)" % (i, ", ".join(args)))
@@ -210,15 +247,6 @@ def read_udfs(pickleSer, infile, eval_type):
     mapper = eval(mapper_str, udfs)
     func = lambda _, it: map(mapper, it)
 
-    if eval_type in (PythonEvalType.SQL_SCALAR_PANDAS_UDF,
-                     PythonEvalType.SQL_GROUPED_MAP_PANDAS_UDF,
-                     PythonEvalType.SQL_GROUPED_AGG_PANDAS_UDF,
-                     PythonEvalType.SQL_WINDOW_AGG_PANDAS_UDF):
-        timezone = utf8_deserializer.loads(infile)
-        ser = ArrowStreamPandasSerializer(timezone)
-    else:
-        ser = BatchedSerializer(PickleSerializer(), 100)
-
     # profiling is not supported for UDF
     return func, None, ser, ser
 

sql/catalyst/src/main/scala/org/apache/spark/sql/internal/SQLConf.scala

@@ -1161,6 +1161,16 @@ object SQLConf {
       .booleanConf
       .createWithDefault(true)
 
+  val PANDAS_GROUPED_MAP_ASSIGN_COLUMNS_BY_POSITION =
+    buildConf("spark.sql.execution.pandas.groupedMap.assignColumnsByPosition")
+      .internal()
+      .doc("When true, a grouped map Pandas UDF will assign columns from the returned " +
+        "Pandas DataFrame based on position, regardless of column label type. When false, " +
+        "columns will be looked up by name if labeled with a string and fallback to use" +
+        "position if not.")
+      .booleanConf
+      .createWithDefault(false)
+
   val REPLACE_EXCEPT_WITH_FILTER = buildConf("spark.sql.optimizer.replaceExceptWithFilter")
     .internal()
     .doc("When true, the apply function of the rule verifies whether the right node of the" +
@@ -1647,6 +1657,9 @@ class SQLConf extends Serializable with Logging {
 
   def pandasRespectSessionTimeZone: Boolean = getConf(PANDAS_RESPECT_SESSION_LOCAL_TIMEZONE)
 
+  def pandasGroupedMapAssignColumnssByPosition: Boolean =
+    getConf(SQLConf.PANDAS_GROUPED_MAP_ASSIGN_COLUMNS_BY_POSITION)
+
   def replaceExceptWithFilter: Boolean = getConf(REPLACE_EXCEPT_WITH_FILTER)
 
   def decimalOperationsAllowPrecisionLoss: Boolean = getConf(DECIMAL_OPERATIONS_ALLOW_PREC_LOSS)

sql/core/src/main/scala/org/apache/spark/sql/execution/arrow/ArrowUtils.scala

@@ -23,6 +23,7 @@ import org.apache.arrow.memory.RootAllocator
 import org.apache.arrow.vector.types.{DateUnit, FloatingPointPrecision, TimeUnit}
 import org.apache.arrow.vector.types.pojo.{ArrowType, Field, FieldType, Schema}
 
+import org.apache.spark.sql.internal.SQLConf
 import org.apache.spark.sql.types._
 
 object ArrowUtils {
@@ -120,4 +121,19 @@ object ArrowUtils {
       StructField(field.getName, dt, field.isNullable)
     })
   }
+
+  /** Return Map with conf settings to be used in ArrowPythonRunner */
+  def getPythonRunnerConfMap(conf: SQLConf): Map[String, String] = {
+    val timeZoneConf = if (conf.pandasRespectSessionTimeZone) {
+      Seq(SQLConf.SESSION_LOCAL_TIMEZONE.key -> conf.sessionLocalTimeZone)
+    } else {
+      Nil
+    }
+    val pandasColsByPosition = if (conf.pandasGroupedMapAssignColumnssByPosition) {
+      Seq(SQLConf.PANDAS_GROUPED_MAP_ASSIGN_COLUMNS_BY_POSITION.key -> "true")
+    } else {
+      Nil
+    }
+    Map(timeZoneConf ++ pandasColsByPosition: _*)
+  }
 }

sql/core/src/main/scala/org/apache/spark/sql/execution/python/AggregateInPandasExec.scala

@@ -28,6 +28,7 @@ import org.apache.spark.sql.catalyst.InternalRow
 import org.apache.spark.sql.catalyst.expressions._
 import org.apache.spark.sql.catalyst.plans.physical.{AllTuples, ClusteredDistribution, Distribution, Partitioning}
 import org.apache.spark.sql.execution.{GroupedIterator, SparkPlan, UnaryExecNode}
+import org.apache.spark.sql.execution.arrow.ArrowUtils
 import org.apache.spark.sql.types.{DataType, StructField, StructType}
 import org.apache.spark.util.Utils
 
@@ -81,7 +82,7 @@ case class AggregateInPandasExec(
     val bufferSize = inputRDD.conf.getInt("spark.buffer.size", 65536)
     val reuseWorker = inputRDD.conf.getBoolean("spark.python.worker.reuse", defaultValue = true)
     val sessionLocalTimeZone = conf.sessionLocalTimeZone
-    val pandasRespectSessionTimeZone = conf.pandasRespectSessionTimeZone
+    val runnerConf = ArrowUtils.getPythonRunnerConfMap(conf)
 
     val (pyFuncs, inputs) = udfExpressions.map(collectFunctions).unzip
 
@@ -135,10 +136,14 @@ case class AggregateInPandasExec(
       }
 
       val columnarBatchIter = new ArrowPythonRunner(
-        pyFuncs, bufferSize, reuseWorker,
-        PythonEvalType.SQL_GROUPED_AGG_PANDAS_UDF, argOffsets, aggInputSchema,
-        sessionLocalTimeZone, pandasRespectSessionTimeZone)
-        .compute(projectedRowIter, context.partitionId(), context)
+        pyFuncs,
+        bufferSize,
+        reuseWorker,
+        PythonEvalType.SQL_GROUPED_AGG_PANDAS_UDF,
+        argOffsets,
+        aggInputSchema,
+        sessionLocalTimeZone,
+        runnerConf).compute(projectedRowIter, context.partitionId(), context)
 
       val joinedAttributes =
         groupingExpressions.map(_.toAttribute) ++ udfExpressions.map(_.resultAttribute)