Initial implementation, using BufferedReader, parallel processing, combining everything in a single go, sorting afterwards (unoptimized)

calculate_average.sh

@@ -17,4 +17,4 @@
 
 
 JAVA_OPTS=""
-java $JAVA_OPTS --class-path target/average-1.0.0-SNAPSHOT.jar dev.morling.onebrc.CalculateAverage
+time java $JAVA_OPTS --class-path target/average-1.0.0-SNAPSHOT.jar dev.morling.onebrc.CalculateAverage

calculate_average_royvanrijn.sh

@@ -0,0 +1,20 @@
+#!/bin/sh
+#
+#  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.
+#
+
+
+JAVA_OPTS=""
+time java $JAVA_OPTS --class-path target/average-1.0.0-SNAPSHOT.jar dev.morling.onebrc.CalculateAverage_royvanrijn

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

@@ -0,0 +1,79 @@
+/*
+ *  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 java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.AbstractMap;
+import java.util.Map;
+import java.util.stream.Collectors;
+
+public class CalculateAverage_royvanrijn {
+
+    private static final String FILE = "./measurements.txt";
+
+    private record Measurement(double min, double max, double sum, long count) {
+
+        Measurement(double initialMeasurement) {
+            this(initialMeasurement, initialMeasurement, initialMeasurement, 1);
+        }
+
+        public static Measurement combineWith(Measurement m1, Measurement m2) {
+            return new Measurement(
+                    m1.min < m2.min ? m1.min : m2.min,
+                    m1.max > m2.max ? m1.max : m2.max,
+                    m1.sum + m2.sum,
+                    m1.count + m2.count
+            );
+        }
+
+        public String toString() {
+            return round(min) + "/" + round(sum / count) + "/" + round(max);
+        }
+
+        private double round(double value) {
+            return Math.round(value * 10.0) / 10.0;
+        }
+    }
+
+    public static void main(String[] args) throws IOException {
+
+//        long before = System.currentTimeMillis();
+
+        Map<String, Measurement> resultMap = Files.lines(Path.of(FILE)).parallel()
+                .map(record -> {
+                    // Map to <String,double>
+                    int pivot = record.indexOf(";");
+                    String key = record.substring(0, pivot);
+                    double measured = Double.parseDouble(record.substring(pivot + 1));
+                    return new AbstractMap.SimpleEntry<>(key, measured);
+                })
+                .collect(Collectors.toConcurrentMap(
+                        // Combine/reduce:
+                        AbstractMap.SimpleEntry::getKey,
+                        entry -> new Measurement(entry.getValue()),
+                        Measurement::combineWith));
+
+        System.out.print("{");
+        System.out.print(
+                resultMap.entrySet().stream().sorted(Map.Entry.comparingByKey()).map(Object::toString).collect(Collectors.joining(", ")));
+        System.out.println("}");
+
+//        System.out.println("Took: " + (System.currentTimeMillis() - before));
+
+    }
+}