How to Count Word Frequencies in Java 8 Using Streams?

Word Frequency Count in Java 8 Using Streams

Counting the frequency of words within a list is a common task in text processing. In Java 8, this can be achieved efficiently using the Collectors.groupingBy() and Collectors.counting() methods.

To find the word frequency in a list of strings, you can use the following steps:

1. Call stream() on the list to create a stream.
2. Group the elements in the stream by their values using Collectors.groupingBy(Function.identity()).
3. Count the occurrences of each word using Collectors.counting().

For example, given the following list of words:

List<String> wordsList = Lists.newArrayList("hello", "bye", "ciao", "bye", "ciao");

You can calculate the word frequencies as follows:

Map<String,Long> wordFrequencies = wordsList.stream()
    .collect(Collectors.groupingBy(Function.identity(), Collectors.counting()));

This will produce a map with the word frequencies, where the keys are the words and the values are the number of occurrences. The result for the given list would be:

{ciao=2, hello=1, bye=2}

To sort the map by values, you can use LinkedHashMap and the entrySet() method to collect the map entries into a stream. Then, use sorted() to sort the entries by value in descending order and Collectors.toMap() to collect them into a new LinkedHashMap:

LinkedHashMap<String, Long> countByWordSorted = wordFrequencies.entrySet()
    .stream()
    .sorted(Map.Entry.comparingByValue(Comparator.reverseOrder()))
    .collect(Collectors.toMap(
        Map.Entry::getKey,
        Map.Entry::getValue,
        (v1, v2) -> { throw new IllegalStateException(); },
        LinkedHashMap::new
    ));

This will produce a sorted map where the words are ordered by their frequency.

The above is the detailed content of How to Count Word Frequencies in Java 8 Using Streams?. For more information, please follow other related articles on the PHP Chinese website!