Github user cloud-fan commented on a diff in the pull request:
https://github.com/apache/spark/pull/9190#discussion_r42977432
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/execution/GroupedIterator.scala ---
@@ -0,0 +1,141 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.sql.execution
+
+import org.apache.spark.sql.catalyst.InternalRow
+import
org.apache.spark.sql.catalyst.expressions.codegen.{GenerateUnsafeProjection,
GenerateOrdering}
+import org.apache.spark.sql.catalyst.expressions.{Attribute, SortOrder,
Ascending, Expression}
+
+object GroupedIterator {
+ def apply(
+ input: Iterator[InternalRow],
+ keyExpressions: Seq[Expression],
+ inputSchema: Seq[Attribute]): Iterator[(InternalRow,
Iterator[InternalRow])] = {
+ if (input.hasNext) {
+ new GroupedIterator(input, keyExpressions, inputSchema)
+ } else {
+ Iterator.empty
+ }
+ }
+}
+
+/**
+ * Iterates over a presorted set of rows, chunking it up by the grouping
expression. Each call to
+ * next will return a pair containing the current group and an iterator
that will return all the
+ * elements of that group. Iterators for each group are lazily
constructed by extracting rows
+ * from the input iterator. As such, full groups are never materialized
by this class.
+ *
+ * Example input:
+ * {{{
+ * Input: [a, 1], [b, 2], [b, 3]
+ * Grouping: x#1
+ * InputSchema: x#1, y#2
+ * }}}
+ *
+ * Result:
+ * {{{
+ * First call to next(): ([a], Iterator([a, 1])
+ * Second call to next(): ([b], Iterator([b, 2], [b, 3])
+ * }}}
+ *
+ * Note, the class does not handle the case of an empty input for
simplicity of implementation.
+ * Use the factory to construct a new instance.
+ *
+ * @param input An iterator of rows. This iterator must be ordered by the
groupingExpressions or
+ * it is possible for the same group to appear more than once.
+ * @param groupingExpressions The set of expressions used to do grouping.
The result of evaluating
+ * these expressions will be returned as the
first part of each call
+ * to `next()`.
+ * @param inputSchema The schema of the rows in the `input` iterator.
+ */
+class GroupedIterator private(
+ input: Iterator[InternalRow],
+ groupingExpressions: Seq[Expression],
+ inputSchema: Seq[Attribute])
+ extends Iterator[(InternalRow, Iterator[InternalRow])] {
+
+ /** Compares two input rows and returns 0 if they are in the same group.
*/
+ val sortOrder = groupingExpressions.map(SortOrder(_, Ascending))
+ val keyOrdering = GenerateOrdering.generate(sortOrder, inputSchema)
+
+ /** Creates a row containing only the key for a given input row. */
+ val keyProjection =
GenerateUnsafeProjection.generate(groupingExpressions, inputSchema)
+
+ /**
+ * Holds null or the row that will be returned on next call to `next()`
in the inner iterator.
+ */
+ var currentRow = input.next()
+
+ /** Holds a copy of an input row that is in the current group. */
+ var currentGroup = currentRow.copy()
+ var currentIterator: Iterator[InternalRow] = null
+ assert(keyOrdering.compare(currentGroup, currentRow) == 0)
+
+ // Return true if we already have the next iterator or fetching a new
iterator is successful.
+ def hasNext: Boolean = currentIterator != null || fetchNextGroupIterator
+
+ def next(): (InternalRow, Iterator[InternalRow]) = {
--- End diff --
What if the user call `next` twice? We will return different result and
break the semantic of `Iterator`
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