Github user tillrohrmann commented on a diff in the pull request:
https://github.com/apache/flink/pull/832#discussion_r32414522
--- 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 --
Well, moving it to `DataSet` means to change the API of Flink and that's
something we first have to decide. Therefore, we first wanted to provide this
functionality as part of a utils class. Since `zipWithIndex` is stateless with
respect to the utils class, it should be `static`. For the Scala API you can,
though, use the pimp my library pattern to allow a syntax `ds.zipWithIndex()`,
with `ds` being some `DataSet`, without having to change the Scala API.
Once we have decided whether these methods shall become part of the API, we
can simply add them to the Java and Scala `DataSet` classes.
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