Combine two Java 8 threads

Question

Is there a way to combine the following 2 statements?

    Map<Integer,Double> collX = listeAllerPunkte.stream().collect(groupingBy(DataPoint::getId,
                                averagingDouble(DataPoint::getX)));
    Map<Integer,Double> collY = listeAllerPunkte.stream().collect(groupingBy(DataPoint::getId,
                                averagingDouble(DataPoint::getY)));

I have a class DataPointsas follows:

public class DataPoint {

    public final double x;
    public final double y;
    private int Id;

    public DataPoint(double x, double y) {
        this.x = x;
        this.y = y;
    }

    public double getX() {
        return x;
    }

    public double getY() {
        return y;
    }

    public int getId() {
        return Id;
    }
}

Idcontains a random value between 0-5.

listeAllerPunkteis Listwith a lot ofDataPoints

Now I want to create DataPointfor everyone DataPointsin the List with the same Id. DataPointshould have a mean value of x and y valuesdatapoints with the same Id.

With two Statemantes from the Beginning, I have to create DataPointsmanually from two Maps. Is there a way to create them directly in the stream?

Answer 1

, . , API, .

, , .

static class DataPointSummary {
    long count;
    double sumX, sumY;

    public double getAverageX() {
        return count==0? 0: sumX/count;
    }
    public double getAverageY() {
        return count==0? 0: sumY/count;
    }
    public void add(DataPoint p) {
        count++;
        sumX+=p.getX();
        sumY+=p.getY();
    }
    public DataPointSummary merge(DataPointSummary s) {
        count+=s.count;
        sumX+=s.sumX;
        sumY+=s.sumY;
        return this;
    }
    @Override
    public String toString() {
        return "DataPointSummary["+count+" points"
            +", avg x="+getAverageX()+", avg y="+getAverageY()+']';
    }
}

,

Map<Integer,DataPointSummary> coll = listeAllerPunkte.stream().collect(
    groupingBy(DataPoint::getId, Collector.of(
        DataPointSummary::new, DataPointSummary::add, DataPointSummary::merge)));

, , public double getId() public int getId(), .

, . , , . , , JRE:

static class DataPointSummary {
    final DoubleSummaryStatistics x=new DoubleSummaryStatistics();
    final DoubleSummaryStatistics y=new DoubleSummaryStatistics();

    public double getAverageX() {
        return x.getAverage();
    }
    public double getAverageY() {
        return y.getAverage();
    }
    public void add(DataPoint p) {
        x.accept(p.getX());
        y.accept(p.getY());
    }
    public DataPointSummary merge(DataPointSummary s) {
        x.combine(s.x);
        y.combine(s.y);
        return this;
    }
    @Override
    public String toString() {
        return "DataPointSummary["+x.getCount()+" points"
            +", avg x="+getAverageX()+", avg y="+getAverageY()+']';
    }
}

, .