feat: first version of the 1brc solution

calculate_average_anandmattikopp.sh

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+#!/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_anandmattikopp

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

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+/*
+ *  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.Paths;
+import java.util.Map;
+import java.util.TreeMap;
+import java.util.stream.Collectors;
+
+public class CalculateAverage_anandmattikopp {
+    private static final String FILE = "./measurements.txt";
+
+    public static void main(String[] args) throws IOException {
+        Map<String, StationStatistics> stationStatisticsMap = Files.lines(Paths.get(FILE)).parallel()
+                .map(entry -> {
+                    String[] tokens = entry.split(";");
+                    return new Station(tokens[0], Double.parseDouble(tokens[1]));
+                })
+                .collect(
+                        Collectors.toConcurrentMap(
+                                station -> station.stationName,
+                                station -> new StationStatistics(station),
+                                StationStatistics::merge));
+
+        System.out.println(new TreeMap<>(stationStatisticsMap));
+    }
+
+    private record Station(String stationName, double temperature) {
+    }
+
+    private record StationStatistics(String stationName, double minTemp, double meanTemp, double maxTemp,
+                                     long totalCount) {
+        StationStatistics(Station station) {
+            //Calling canonical constructor
+            this(station.stationName, station.temperature, station.temperature, station.temperature, 1);
+        }
+
+        //Merging two stats to create new stats
+        public static StationStatistics merge(StationStatistics stats1, StationStatistics stats2) {
+            assert stats1.stationName.equals(stats2.stationName);
+            return new StationStatistics(
+                    stats1.stationName,
+                    Math.min(stats1.minTemp, stats2.minTemp), // minimum of both the temp
+                    (stats1.meanTemp * stats1.totalCount + stats2.meanTemp * stats2.totalCount) / (stats1.totalCount + stats2.totalCount), // average of both the average temps from stats
+                    Math.max(stats1.maxTemp, stats2.maxTemp), // maximum of both the temp
+                    stats1.totalCount + stats2.totalCount // increment the totalCount
+            );
+        }
+
+        @Override
+        public String toString() {
+            return round(minTemp) + "/" + round(meanTemp) + "/" + round(maxTemp);
+        }
+
+        private double round(double value) {
+            return Math.round(value * 10.0) / 10.0;
+        }
+    }
+}