#49 Fixing rounding behavior of baseline implementation

src/main/java/dev/morling/onebrc/CalculateAverage_baseline.java

@@ -35,6 +35,7 @@ public class CalculateAverage_baseline {
     }
 
     private static record ResultRow(double min, double mean, double max) {
+
         public String toString() {
             return round(min) + "/" + round(mean) + "/" + round(max);
         }
@@ -79,7 +80,7 @@ public class CalculateAverage_baseline {
                     return res;
                 },
                 agg -> {
-                    return new ResultRow(agg.min, agg.sum / agg.count, agg.max);
+                    return new ResultRow(agg.min, (Math.round(agg.sum * 10.0) / 10.0) / agg.count, agg.max);
                 });
 
         Map<String, ResultRow> measurements = new TreeMap<>(Files.lines(Paths.get(FILE))

src/main/java/dev/morling/onebrc/CalculateAverage_baseline_original_rounding.java

@@ -0,0 +1,100 @@
+/*
+ *  Copyright 2023 The original authors
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+package dev.morling.onebrc;
+
+import static java.util.stream.Collectors.*;
+
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Paths;
+import java.util.Map;
+import java.util.TreeMap;
+import java.util.stream.Collector;
+
+/**
+ * This is the original version of the baseline implementation. It contains a
+ * rounding bug, which can cause calculated mean values to be off by 0.1. See
+ * {@link CalculateAverage_baseline} for the correct behavior. This version here
+ * is only kept for reference, in particular for determining whether an
+ * implementation is valid with the old behavior. Any new or updated entries to
+ * the challenge must conform to the correct behavior as implemented by
+ * {@code CalculateAverage_baseline}.
+ */
+public class CalculateAverage_baseline_original_rounding {
+
+    private static final String FILE = "./measurements.txt";
+
+    private static record Measurement(String station, double value) {
+        private Measurement(String[] parts) {
+            this(parts[0], Double.parseDouble(parts[1]));
+        }
+    }
+
+    private static record ResultRow(double min, double mean, double max) {
+        public String toString() {
+            return round(min) + "/" + round(mean) + "/" + round(max);
+        }
+
+        private double round(double value) {
+            return Math.round(value * 10.0) / 10.0;
+        }
+    };
+
+    private static class MeasurementAggregator {
+        private double min = Double.POSITIVE_INFINITY;
+        private double max = Double.NEGATIVE_INFINITY;
+        private double sum;
+        private long count;
+    }
+
+    public static void main(String[] args) throws IOException {
+        // Map<String, Double> measurements1 = Files.lines(Paths.get(FILE))
+        // .map(l -> l.split(";"))
+        // .collect(groupingBy(m -> m[0], averagingDouble(m -> Double.parseDouble(m[1]))));
+        //
+        // measurements1 = new TreeMap<>(measurements1.entrySet()
+        // .stream()
+        // .collect(toMap(e -> e.getKey(), e -> Math.round(e.getValue() * 10.0) / 10.0)));
+        // System.out.println(measurements1);
+
+        Collector<Measurement, MeasurementAggregator, ResultRow> collector = Collector.of(
+                MeasurementAggregator::new,
+                (a, m) -> {
+                    a.min = Math.min(a.min, m.value);
+                    a.max = Math.max(a.max, m.value);
+                    a.sum += m.value;
+                    a.count++;
+                },
+                (agg1, agg2) -> {
+                    var res = new MeasurementAggregator();
+                    res.min = Math.min(agg1.min, agg2.min);
+                    res.max = Math.max(agg1.max, agg2.max);
+                    res.sum = agg1.sum + agg2.sum;
+                    res.count = agg1.count + agg2.count;
+
+                    return res;
+                },
+                agg -> {
+                    return new ResultRow(agg.min, agg.sum / agg.count, agg.max);
+                });
+
+        Map<String, ResultRow> measurements = new TreeMap<>(Files.lines(Paths.get(FILE))
+                .map(l -> new Measurement(l.split(";")))
+                .collect(groupingBy(m -> m.station(), collector)));
+
+        System.out.println(measurements);
+    }
+}