Create a histogram of people's balances using Spark

Histogram.java

class CDA {
	String creditor;
	String debtor;
	int amount;
}

public List<Tuple2<Integer, Integer>> createHistogram(JavaRDD<CDA> inputRDD) {
	return inputRDD
		.flatMapToPair(cda -> Arrays.asList(
			new Tuple2<>(cda.creditor, cda.amount),
			new Tuple2<>(cda.debtor, -cda.amount)))
		.reduceByKey(Integer::sum)
		.mapToPair(pa -> new Tuple2<>(pa._2 / 1000, 1))
		.reduceByKey(Integer::sum)
		.sortByKey(true, 1)
		.collect();
}