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Java example source code file (FoldWithinPartitionFunction.java)

This example Java source code file (FoldWithinPartitionFunction.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

accumulator, arraylist, atomiclong, counter, exception, foldwithinpartitionfunction, function2, iterator, list, override, util

The FoldWithinPartitionFunction.java Java example source code

package org.deeplearning4j.spark.text.functions;

import org.apache.spark.Accumulator;
import org.apache.spark.api.java.function.Function2;
import org.deeplearning4j.berkeley.Counter;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.concurrent.atomic.AtomicLong;

/**
 * @author jeffreytang
 */
public class FoldWithinPartitionFunction implements Function2<Integer, Iterator> {

    public FoldWithinPartitionFunction(Accumulator<Counter maxPartitionAcc) {
        this.maxPerPartitionAcc = maxPartitionAcc;
    }

    private Accumulator<Counter maxPerPartitionAcc;


    @Override
    public Iterator<AtomicLong> call(Integer ind, Iterator partition) throws Exception {

        List<AtomicLong> foldedItemList = new ArrayList() {{ add(new AtomicLong(0L)); }};

        // Recurrent state implementation of cum sum
        int foldedItemListSize = 1;
        while (partition.hasNext()) {
            long curPartitionItem = partition.next().get();
            int lastFoldedIndex = foldedItemListSize - 1;
            long lastFoldedItem = foldedItemList.get(lastFoldedIndex).get();
            AtomicLong sumLastCurrent = new AtomicLong(curPartitionItem + lastFoldedItem);

            foldedItemList.set(lastFoldedIndex, sumLastCurrent);
            foldedItemList.add(sumLastCurrent);
            foldedItemListSize += 1;
        }

        // Update Accumulator
        long maxFoldedItem = foldedItemList.remove(foldedItemListSize - 1).get();
        Counter<Integer> partitionIndex2maxItemCounter = new Counter<>();
        partitionIndex2maxItemCounter.incrementCount(ind, maxFoldedItem);
        maxPerPartitionAcc.add(partitionIndex2maxItemCounter);

        return foldedItemList.iterator();
    }
}

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