Github user fhueske commented on a diff in the pull request:
https://github.com/apache/flink/pull/1255#discussion_r43951890
--- Diff:
flink-java/src/main/java/org/apache/flink/api/java/functions/RangeBoundaryBuilder.java
---
@@ -0,0 +1,71 @@
+/*
+ * 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.flink.api.java.functions;
+
+import org.apache.flink.api.common.distributions.CommonRangeBoundaries;
+import org.apache.flink.api.common.distributions.RangeBoundaries;
+import org.apache.flink.api.common.functions.RichMapPartitionFunction;
+import org.apache.flink.api.common.typeutils.TypeComparator;
+import org.apache.flink.api.common.typeutils.TypeComparatorFactory;
+import org.apache.flink.util.Collector;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.Comparator;
+import java.util.List;
+
+/**
+ * Build RangeBoundaries with input records. First, sort the input
records, and then select
+ * the boundaries with same interval.
+ *
+ * @param <T>
+ */
+public class RangeBoundaryBuilder<T> extends RichMapPartitionFunction<T,
RangeBoundaries<T>> {
+
+ private int parallelism;
+ private final TypeComparatorFactory<T> comparatorFactory;
+
+ public RangeBoundaryBuilder(TypeComparatorFactory<T> comparator, int
parallelism) {
+ this.comparatorFactory = comparator;
+ this.parallelism = parallelism;
+ }
+
+ @Override
+ public void mapPartition(Iterable<T> values,
Collector<RangeBoundaries<T>> out) throws Exception {
+ final TypeComparator<T> comparator =
this.comparatorFactory.createComparator();
+ List<T> sampledData = new ArrayList<>();
+ for (T value : values) {
+ sampledData.add(value);
+ }
+ Collections.sort(sampledData, new Comparator<T>() {
+ @Override
+ public int compare(T first, T second) {
+ return comparator.compare(first, second);
+ }
+ });
+
+ List<T> boundaries = new ArrayList<>();
+ double avgRange = sampledData.size() / (double) parallelism;
+ for (int i = 1; i < parallelism; i++) {
+ boundaries.add(sampledData.get((int) (i * avgRange)));
+ }
+
+ RangeBoundaries<T> rangeBoundaries = new
CommonRangeBoundaries<>(boundaries);
--- End diff --
It might be better to send the boundaries as individual records instead of
a single big record.
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