How can I efficiently count word frequency in a list using Java 8?

Counting Word Frequency with Java 8

In web development and data analysis, understanding the frequency of words is crucial. To achieve this, we'll delve into how to count the frequency of words in a list using Java 8.

Java 8 Solution

The Stream API in Java 8 provides an elegant solution for word frequency counting. To begin, create a list of words:

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

The core logic involves grouping the words by their identity and counting the occurrences:

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

This produces a map where each key is a unique word, and the corresponding value is its frequency. The output should resemble:

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

Counting Integer Values

If you require integer values instead of long values, use:

Map<String, Integer> collect = wordsList.stream()
     .collect(Collectors.groupingBy(Function.identity(), Collectors.summingInt(e -> 1)));

Sorting the Map by Value

To sort the map based on values in descending order, use:

LinkedHashMap<String, Long> countByWordSorted = collect.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 step returns a sorted LinkedHashMap where the keys represent the words, and the values represent their sorted frequencies.

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