Tag: map-reduce

Following code snippet shows how you can write a word count program using Java 8 Stream API.

public class WordCountExample {

    public static void main(String[] args) throws IOException {
        Path path = Paths.get("src/main/resources/book.txt");
        Map<String, Integer> wordCount = Files.lines(path)
           .flatMap(line -> Arrays.stream(line.trim().split(" ")))
           .map(word -> word.replaceAll("[^a-zA-Z]", "").toLowerCase().trim())
           .filter(word -> word.length() > 0)
           .map(word -> new SimpleEntry<>(word, 1))
           .sorted((e1, e2) -> e1.getKey().compareTo(e2.getKey()))
            .reduce(new LinkedHashMap<>(), (acc, entry) -> {
               acc.put(entry.getKey(), acc.compute(entry.getKey(), (k, v) -> v == null ? 1 : v + 1));
               return acc;
            }, (m1, m2) -> m1);

        wordCount.forEach((k, v) -> System.out.println(String.format("%s ==>> %d", k, v)));
    }
}

The better solution is using toMap collector as shown below.

public static void main(String[] args) throws IOException {
   Path path = Paths.get("src/main/resources/book.txt");
   Map<String, Integer> wordCount = Files.lines(path).flatMap(line -> Arrays.stream(line.trim().split("s")))
           .map(word -> word.replaceAll("[^a-zA-Z]", "").toLowerCase().trim())
           .filter(word -> word.length() > 0)
           .map(word -> new SimpleEntry<>(word, 1))
           .collect(toMap(e -> e.getKey(), e -> e.getValue(), (v1, v2) -> v1 + v2));

   wordCount.forEach((k, v) -> System.out.println(String.format("%s ==>> %d", k, v)));
}

Even better version can be written using grouping and counting collector as shown below.

public static void main(String[] args) throws IOException {
    Path path = Paths.get("src/main/resources/book.txt");
    Map<String, Long> wordCount = Files.lines(path).flatMap(line -> Arrays.stream(line.trim().split("\s")))
            .map(word -> word.replaceAll("[^a-zA-Z]", "").toLowerCase().trim())
            .filter(word -> word.length() > 0)
            .map(word -> new SimpleEntry<>(word, 1))
            .collect(groupingBy(SimpleEntry::getKey, counting()));

    wordCount.forEach((k, v) -> System.out.println(String.format("%s ==>> %d", k, v)));

}