Github user fhueske commented on a diff in the pull request:
https://github.com/apache/flink/pull/832#discussion_r32415043
--- Diff:
flink-java/src/main/java/org/apache/flink/api/java/utils/DataSetUtils.java ---
@@ -0,0 +1,106 @@
+/*
+ * 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.utils;
+
+import org.apache.flink.api.common.functions.RichMapPartitionFunction;
+import org.apache.flink.api.java.DataSet;
+import org.apache.flink.api.java.tuple.Tuple2;
+import org.apache.flink.configuration.Configuration;
+import org.apache.flink.util.Collector;
+
+import java.util.Collections;
+import java.util.Comparator;
+import java.util.List;
+
+/**
+ * This class provides simple utility methods for zipping elements in a
file with an index.
+ *
+ * @param <T> The type of the DataSet, i.e., the type of the elements of
the DataSet.
+ */
+public class DataSetUtils<T> {
+
+ /**
+ * Method that goes over all the elements in each partition in order to
retireve
+ * the total number of elements.
+ *
+ * @param input the DataSet received as input
+ * @return a data set containing tuples of subtask index, number of
elements mappings.
+ */
+ public DataSet<Tuple2<Integer, Long>> countElements(DataSet<T> input) {
+ return input.mapPartition(new RichMapPartitionFunction<T,
Tuple2<Integer,Long>>() {
+ @Override
+ public void mapPartition(Iterable<T> values,
Collector<Tuple2<Integer, Long>> out) throws Exception {
+ long counter = 0;
+ for(T value: values) {
+ counter ++;
+ }
+
+ out.collect(new Tuple2<Integer,
Long>(getRuntimeContext().getIndexOfThisSubtask(), counter));
+ }
+ });
+ }
+
+ /**
+ * Method that takes a set of subtask index, total number of elements
mappings
+ * and assigns ids to all the elements from the input data set.
+ *
+ * @param input the input data set
+ * @return a data set of tuple 2 consisting of consecutive ids and
initial values.
+ */
+ public DataSet<Tuple2<Long, T>> zipWithIndex(DataSet<T> input) {
--- End diff --
The reason for not having it in the core API is to keep that API slim and
not to overload it with functionality that is not very often used (which is not
always easy to decide). The pimp-my-lib pattern is useful if you cannot change
the API directly (which we could). If we pimp the API, we could also move it
directly to DataSet.
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