Counting word occurrences in a text file. - Java Lambda Stream

Java examples for Lambda Stream:Collector

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Description

Counting word occurrences in a text file.

Demo Code

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.regex.Pattern;
import java.util.stream.Collectors;

public class Main
{
   public static void main(String[] args) throws IOException
   {/*from   w ww .  j av a 2s.co m*/
      // Regex that matches one or more consecutive whitespace characters
      Pattern pattern = Pattern.compile("\\s+"); 

      // count occurrences of each word in a Stream<String> sorted by word
      Map<String, Long> wordCounts = 
         Files.lines(Paths.get("Chapter2Paragraph.txt"))
              .map(line -> line.replaceAll("(?!')\\p{P}", ""))
              .flatMap(line -> pattern.splitAsStream(line))
              .collect(Collectors.groupingBy(String::toLowerCase,
                 TreeMap::new, Collectors.counting()));
      
      // display the words grouped by starting letter
      wordCounts.entrySet()
         .stream()
         .collect(
            Collectors.groupingBy(entry -> entry.getKey().charAt(0), 
               TreeMap::new, Collectors.toList()))
         .forEach((letter, wordList) -> 
            { 
               System.out.printf("%n%C%n", letter);
               wordList.stream().forEach(word -> System.out.printf(
                  "%13s: %d%n", word.getKey(), word.getValue()));
            });
   }
}

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