CalculateAverage_javamak (#360)

1 files changed, 158 insertions, 0 deletions

diff --git a/src/main/java/dev/morling/onebrc/CalculateAverage_javamak.java b/src/main/java/dev/morling/onebrc/CalculateAverage_javamak.java
new file mode 100644
index 0000000..84c0714
--- /dev/null
+++ b/src/main/java/dev/morling/onebrc/CalculateAverage_javamak.java
@@ -0,0 +1,158 @@
+/*
+ *  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.ByteBuffer;
+import java.nio.channels.FileChannel;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.nio.file.StandardOpenOption;
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.TreeMap;
+import java.util.stream.Collector;
+import java.util.stream.Stream;
+
+public class CalculateAverage_javamak {
+
+    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 -> new ResultRow(agg.min, agg.sum / agg.count, agg.max));
+
+        var path = Paths.get(FILE);
+
+        var a = calcChunks(path).entrySet().parallelStream()
+                .flatMap(entry -> getLinesFromFile(path, entry)) // read file for each chunk and get the lines
+                .map(l -> new Measurement(l.split(";")))// convert each line to measurement object
+                .collect(groupingBy(Measurement::station, collector));
+        Map<String, ResultRow> measurements = new TreeMap<>(a);
+
+        System.out.println(measurements);
+    }
+
+    private static Stream<String> getLinesFromFile(Path path, Map.Entry<Long, Long> entry) {
+        try (FileChannel channel = FileChannel.open(path, StandardOpenOption.READ)) {
+            channel.position(entry.getKey());
+            ByteBuffer buffer = ByteBuffer.allocate((int) (entry.getValue() - entry.getKey() + 1));
+            channel.read(buffer);
+            String chunk = new String(buffer.array());
+            return Arrays.stream(chunk.split("\n"));
+        }
+        catch (IOException e) {
+            throw new RuntimeException(e);
+        }
+    }
+
+    private static Map<Long, Long> calcChunks(Path path) throws IOException {
+        long startPos = 0;
+        Map<Long, Long> retMap = new HashMap<>();
+        while (true) {
+            long endPos = calculateEndPosition(path, startPos, 1000 * 5000);
+            if (endPos == -1) {
+                break;
+            }
+            long finalStartPos = startPos;
+            retMap.put(finalStartPos, endPos);
+            startPos = endPos + 1;
+        }
+        return retMap;
+    }
+
+    private static long calculateEndPosition(Path path, long startPos, long chunkSize) throws IOException {
+        try (FileChannel channel = FileChannel.open(path, StandardOpenOption.READ)) {
+            if (startPos >= channel.size()) {
+                return -1;
+            }
+
+            long currentPos = startPos + chunkSize;
+            if (currentPos >= channel.size()) {
+                currentPos = channel.size() - 1;
+            }
+
+            channel.position(currentPos);
+            ByteBuffer buffer = ByteBuffer.allocate(1024);
+            int readBytes = channel.read(buffer);
+
+            if (readBytes > 0) {
+                for (int i = 0; i < readBytes; i++) {
+                    if (buffer.get(i) == '\n') {
+                        break;
+                    }
+                    currentPos++;
+                }
+            }
+
+            return currentPos;
+        }
+    }
+}