Spark Combinebykey Espressione lambda JAVA

Question

Desidero utilizzare la funzione lambda per calcolare la media mediante una chiave (JavaPairRDD<Integer, Double> pairs). Per questo motivo, ho sviluppato il codice seguente:

java.util.function.Function<Double, Tuple2<Double, Integer>> createAcc = x -> new Tuple2<Double, Integer>(x, 1); 

BiFunction<Tuple2<Double, Integer>, Double, Tuple2<Double, Integer>> addAndCount = (Tuple2<Double, Integer> x, Double y) -> { return new Tuple2(x._1()+y, x._2()+1); }; 

BiFunction<Tuple2<Double, Integer>, Tuple2<Double, Integer>, Tuple2<Double, Integer>> combine = (Tuple2<Double, Integer> x, Tuple2<Double, Integer> y) -> { return new Tuple2(x._1()+y._1(), x._2()+y._2()); }; 

JavaPairRDD<Integer, Tuple2<Double, Integer>> avgCounts = pairs.combineByKey(createAcc, addAndCount, combine); 

Tuttavia, eclisse diplays questo errore:

The method combineByKey(Function<Double,C>, Function2<C,Double,C>, Function2<C,C,C>) in the type JavaPairRDD<Integer,Double> is not applicable for the arguments (Function<Double,Tuple2<Double,Integer>>, 
BiFunction<Tuple2<Double,Integer>,Double,Tuple2<Double,Integer>>, BiFunction<Tuple2<Double,Integer>,Tuple2<Double,Integer>,Tuple2<Double,Integer>>) 

Answer 1

Procedimento combineByKey aspetta org.apache.spark.api.java.function.Function2 anziché java.util.function.BiFunction. Quindi, o si scrive:

java.util.function.Function<Double, Tuple2<Double, Integer>> createAcc = 
    x -> new Tuple2<Double, Integer>(x, 1); 

Function2<Tuple2<Double, Integer>, Double, Tuple2<Double, Integer>> addAndCount = 
    (Tuple2<Double, Integer> x, Double y) -> { return new Tuple2(x._1()+y, x._2()+1); }; 

Function2<Tuple2<Double, Integer>, Tuple2<Double, Integer>, Tuple2<Double, Integer>> combine = 
    (Tuple2<Double, Integer> x, Tuple2<Double, Integer> y) -> { return new Tuple2(x._1()+y._1(), x._2()+y._2()); }; 

JavaPairRDD<Integer, Tuple2<Double, Integer>> avgCounts = 
    pairs.combineByKey(createAcc, addAndCount, combine);