Calculate weighted average with Java 8 streams

Question

How do I go about calculating weighted mean of a Map where the Integer value is the weight for the Double value to be averaged. eg: Map h

Answer 1

public static double weightedAvg(Collection data) {
    var sumWeights = data.stream()
        .map(Map.Entry::getKey)
        .mapToDouble(Number::doubleValue)
        .sum();
    var sumData = data.stream()
        .mapToDouble(e -> e.getKey().doubleValue() * e.getValue().doubleValue())
        .sum();
    return sumData / sumWeights;
}