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From: tillrohrmann <git@git.apache.org>
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Subject: [GitHub] flink pull request: [FLINK-2152] Added zipWithIndex 
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Message-Id: <20150615123257.76AD9E04D7@git1-us-west.apache.org>
Date: Mon, 15 Jun 2015 12:32:57 +0000 (UTC)

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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