sirdan sirdan -4 years ago 128
Java Question

Sorting a JavaDStream - Spark Streaming

I have an application which works with

This is a piece of code, where I compute the frequencies the words appear with.

JavaPairDStream<String, Integer> wordCounts = words.mapToPair(
new PairFunction<String, String, Integer>() {
public Tuple2<String, Integer> call(String s) {
return new Tuple2<>(s, 1);
}).reduceByKey(new Function2<Integer, Integer, Integer>() {
public Integer call(Integer i1, Integer i2) {
return i1 + i2;

Now, if I wished to print the top N frequent elements, sorted by the Integer value, how can I do this if there's not methods like sortByKey (for JavaPairRDD)?

Answer Source

As you have JavaPairDStream<String, Integer> and want to sort by Integer value, you have to swap pair first.

JavaPairDStream<Integer,String> swappedPair = wordCounts.mapToPair(x -> x.swap());

Now you can sort by using transformToPair and use sortByKey function.

JavaPairDStream<Integer,String> sortedStream = swappedPair.transformToPair(
     new Function<JavaPairRDD<Integer,String>, JavaPairRDD<Integer,String>>() {
         public JavaPairRDD<Integer,String> call(JavaPairRDD<Integer,String> jPairRDD) throws Exception {
                    return jPairRDD.sortByKey(false);

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