README update

README.md

@@ -1,6 +1,6 @@
 # 1️⃣🐝🏎️ The One Billion Row Challenge
 
-_Note: The challenge will be opened officially on Jan 1 2024!_
+_Status Jan 1: This challenge is open for submissions!_
 
 The One Billion Row Challenge (1BRC) is a fun exploration of how far modern Java can be pushed for aggregating one billion rows from a text file.
 Grab all your (virtual) threads, reach out to SIMD, optimize your GC, or pull any other trick, and create the fastest implementation for solving this task!
@@ -22,10 +22,11 @@ Conakry;31.2
 Istanbul;23.0
 ```
 
-The task is to write a Java program which reads the file, calculates the average temperature value per weather station, and emits the result on stdout like this, sorted alphabetically by station name:
+The task is to write a Java program which reads the file, calculates the min, mean, and max temperature value per weather station, and emits the results on stdout like this
+(i.e. sorted alphabetically by station name, and the result values per station in the format `<min>/<mean>/<max>`, rounded to one fractional digit):
 
 ```
-{Abha=18.0, Abidjan=26.0, Abéché=29.4, Accra=26.4, Addis Ababa=16.0, Adelaide=17.3, ...}
+{Abha=-23.0/18.0/59.2, Abidjan=-16.2/26.0/67.3, Abéché=-10.0/29.4/69.0, Accra=-10.1/26.4/66.4, Addis Ababa=-23.7/16.0/67.0, Adelaide=-27.8/17.3/58.5, ...}
 ```
 
 Submit your implementation by Jan 31 2024 and become part of the leaderboard!

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

@@ -15,28 +15,76 @@
  */
 package dev.morling.onebrc;
 
-import static java.util.stream.Collectors.averagingDouble;
-import static java.util.stream.Collectors.groupingBy;
+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.Collectors;
+import java.util.stream.Collector;
 
 public class CalculateAverage {
 
     private static final String FILE = "./measurements.txt";
 
-    public static void main(String[] args) throws IOException {
-        Map<String, Double> measurements = Files.lines(Paths.get(FILE))
-                .map(l -> l.split(";"))
-                .collect(groupingBy(m -> m[0], averagingDouble(m -> Double.parseDouble(m[1]))));
+    private static record Measurement(String station, double value) {
+        private Measurement(String[] parts) {
+            this(parts[0], Double.parseDouble(parts[1]));
+        }
+    }
 
-        measurements = new TreeMap<>(measurements.entrySet()
-                .stream()
-                .collect(Collectors.toMap(e -> e.getKey(), e -> Math.round(e.getValue() * 10.0) / 10.0)));
+    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);
     }

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

@@ -77,9 +77,9 @@ public class CreateMeasurements {
         // ) TO 'output.csv' (HEADER, DELIMITER ',');
         // @formatter:on
         List<WeatherStation> stations = Arrays.asList(
-                new WeatherStation("Abéché", 29.4),
                 new WeatherStation("Abha", 18.0),
                 new WeatherStation("Abidjan", 26.0),
+                new WeatherStation("Abéché", 29.4),
                 new WeatherStation("Accra", 26.4),
                 new WeatherStation("Addis Ababa", 16.0),
                 new WeatherStation("Adelaide", 17.3),