From 0d5d262cf4cd9143dd275fc6a2d8ea1b8dd79959 Mon Sep 17 00:00:00 2001
From: Daniel Schramm <xschramm@fi.muni.cz>
Date: Mon, 11 Oct 2021 19:08:29 +0200
Subject: [PATCH] Collector for computation of the weighted average implemented
---
.../face/WeightedAverageCollector.java | 135 ++++++++++++++++++
1 file changed, 135 insertions(+)
create mode 100644 Comparison/src/main/java/cz/fidentis/analyst/visitors/face/WeightedAverageCollector.java
diff --git a/Comparison/src/main/java/cz/fidentis/analyst/visitors/face/WeightedAverageCollector.java b/Comparison/src/main/java/cz/fidentis/analyst/visitors/face/WeightedAverageCollector.java
new file mode 100644
index 00000000..2ef46945
--- /dev/null
+++ b/Comparison/src/main/java/cz/fidentis/analyst/visitors/face/WeightedAverageCollector.java
@@ -0,0 +1,135 @@
+package cz.fidentis.analyst.visitors.face;
+
+import java.util.Set;
+import java.util.function.BiConsumer;
+import java.util.function.BinaryOperator;
+import java.util.function.Function;
+import java.util.function.Supplier;
+import java.util.function.ToDoubleFunction;
+import java.util.stream.Collector;
+
+/**
+ * A collector for computing weighted average suitable for use in Java 8 streams.
+ *
+ * <p>
+ * A mutable reduction operation that accumulates input elements into a mutable
+ * result container, optionally transforming the accumulated result into a final
+ * representation after all input elements have been processed.
+ * </p>
+ *
+ * @author Daniel Schramm
+ * @param <T> Data type of the stream elements
+ */
+public class WeightedAverageCollector<T> implements Collector<T, IntemediateResults, Double> {
+
+ private final ToDoubleFunction<? super T> valueFunction, weightFunction;
+
+ /**
+ * Constructor.
+ *
+ * @param valueFunction Function returning the value for a given stream element
+ * @param weightFunction Function returning the weight for a given stream element
+ */
+ public WeightedAverageCollector(
+ ToDoubleFunction<? super T> valueFunction,
+ ToDoubleFunction<? super T> weightFunction) {
+ this.valueFunction = valueFunction;
+ this.weightFunction = weightFunction;
+ }
+
+ /**
+ * Returns a {@link Collector} interface object used to compute the weighted average.
+ *
+ * @param <T> Data type of the stream elements
+ * @param valueFunction Function returning the value for a given stream element
+ * @param weightFunction Function returning the weight for a given stream element
+ * @return A Collector interface object used to compute the weighted average
+ */
+ public static <T> Collector<T, ?, Double> toWeightedAverage(
+ ToDoubleFunction<? super T> valueFunction,
+ ToDoubleFunction<? super T> weightFunction) {
+ return new WeightedAverageCollector(valueFunction, weightFunction);
+ }
+
+ /**
+ * A function that creates and returns a new mutable result container.
+ *
+ * @return A function which returns a new, mutable result container
+ */
+ @Override
+ public Supplier<IntemediateResults> supplier() {
+ return IntemediateResults::new;
+ }
+
+ /**
+ * A function that folds a value into a mutable result container.
+ *
+ * @return A function which folds a value into a mutable result container
+ */
+ @Override
+ public BiConsumer<IntemediateResults, T> accumulator() {
+ return (result, streamElement) -> {
+ result.weightedValSum += valueFunction.applyAsDouble(streamElement)
+ * weightFunction.applyAsDouble(streamElement);
+ result.weightSum += weightFunction.applyAsDouble(streamElement);
+ };
+ }
+
+ /**
+ * A function that accepts two partial results and merges them. The
+ * combiner function may fold state from one argument into the other and
+ * return that, or may return a new result container.
+ *
+ * @return A function which combines two partial results into a combined
+ * result
+ */
+ @Override
+ public BinaryOperator<IntemediateResults> combiner() {
+ return (result1, result2) -> {
+ result1.weightedValSum += result2.weightedValSum;
+ result1.weightSum += result2.weightSum;
+
+ return result1;
+ };
+ }
+
+ /**
+ * Perform the final transformation from the intermediate accumulation type
+ * {@code A} to the final result type {@code R}.
+ *
+ * <p>
+ * If the characteristic {@code IDENTITY_FINISH} is
+ * set, this function may be presumed to be an identity transform with an
+ * unchecked cast from {@code A} to {@code R}.
+ * </p>
+ *
+ * @return A function which transforms the intermediate result to the final
+ * result
+ */
+ @Override
+ public Function<IntemediateResults, Double> finisher() {
+ return result -> result.weightedValSum / result.weightSum;
+ }
+
+ /**
+ * Returns a {@code Set} of {@code Collector.Characteristics} indicating
+ * the characteristics of this Collector.
+ *
+ * @return An immutable set of collector characteristics
+ */
+ @Override
+ public Set<Characteristics> characteristics() {
+ return Set.of(Characteristics.UNORDERED);
+ }
+}
+
+/**
+ * A helper class which stores intermediate results
+ * for the {@link WeightedAverageCollector} class.
+ *
+ * @author Daniel Schramm
+ */
+class IntemediateResults {
+ double weightedValSum = 0;
+ double weightSum = 0;
+}
--
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