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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 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;
}
}
}
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