test: add histogram (1 000 000 CUID)

Author: thibaultmeyer

src/test/java/io/github/thibaultmeyer/cuid/HistogramTest.java

@@ -0,0 +1,97 @@
+package io.github.thibaultmeyer.cuid;
+
+import org.junit.jupiter.api.MethodOrderer;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.TestMethodOrder;
+
+import java.util.DoubleSummaryStatistics;
+import java.util.List;
+import java.util.Map;
+import java.util.function.Function;
+import java.util.stream.Collectors;
+import java.util.stream.IntStream;
+import java.util.stream.Stream;
+
+@TestMethodOrder(MethodOrderer.MethodName.class)
+final class HistogramTest {
+
+    @Test
+    void histogramCUIDv1() {
+
+        // Arrange
+        final List<Double> data = Stream.generate(CUID::randomCUID1)
+            .limit(1_000_000)
+            .map(Object::hashCode)
+            .map(o -> (double) o)
+            .collect(Collectors.toList());
+
+        // Act
+        final Histogram histogram = new Histogram(data);
+        final Map<Integer, Integer> frequencies = histogram.histogram(20);
+
+        // Assert
+        System.out.println("CUID v1: " + frequencies);
+    }
+
+    @Test
+    void histogramCUIDv2() {
+
+        // Arrange
+        final List<Double> data = Stream.generate(CUID::randomCUID2)
+            .limit(1_000_000)
+            .map(Object::hashCode)
+            .map(o -> (double) o)
+            .collect(Collectors.toList());
+
+        // Act
+        final Histogram histogram = new Histogram(data);
+        final Map<Integer, Integer> frequencies = histogram.histogram(20);
+
+        // Assert
+        System.out.println("CUID v2: " + frequencies);
+    }
+
+    public static final class Histogram {
+
+        private final List<Double> data;
+
+        public Histogram(List<Double> data) {
+
+            this.data = data;
+        }
+
+        private static Integer findBin(Double datum, int bins, double min, double max) {
+
+            final double binWidth = (max - min) / bins;
+            if (datum >= max) {
+                return bins - 1;
+            } else if (datum <= min) {
+                return 0;
+            }
+            return (int) Math.floor((datum - min) / binWidth);
+        }
+
+        public Map<Integer, Integer> histogram(int bins) {
+
+            final DoubleSummaryStatistics statistics = this.data.stream()
+                .mapToDouble(x -> x)
+                .summaryStatistics();
+
+            final double max = statistics.getMax();
+            final double min = statistics.getMin();
+
+            // Make sure that all bins are initialized
+            final Map<Integer, Integer> histogram = IntStream.range(0, bins)
+                .boxed()
+                .collect(Collectors.toMap(Function.identity(), x -> 0));
+
+            histogram.putAll(
+                this.data.stream().collect(
+                    Collectors.groupingBy(
+                        x -> findBin(x, bins, min, max),
+                        Collectors.mapping(x -> 1, Collectors.summingInt(x -> x)))));
+
+            return histogram;
+        }
+    }
+}