How to get unique values with frequency from List<String[]> in Java?

Question

I want to get unique values from a List<String[]> and store them in a new list (or HashMap<String, Integer> where String is the unique value and Integer is its number of occurrences in the List<String[]> . How can I extract the unique values?

Answer 1

You can use Collectors.groupingBy

Map<String, Long> map = abc.stream()
                           .flatMap(Arrays::stream)
                           .collect(Collectors.groupingBy(Function.identity(),
                                       Collectors.counting()));

Answer 2

If you are using Java 8 or above it's pretty easy. (Slight correction using the other answer)

List<String[]> abc = new ArrayList<>();
String[] string1 = {"123", "567"};
String[] string2 = {"123", "456"};
abc.add(string1);
abc.add(string2);

List<String> newList = abc.stream()
        .flatMap(Arrays::stream)
        .distinct()
        .collect(Collectors.toList());

Map<String, Long> hashMap = abc.stream()
            .flatMap(Arrays::stream)
            .collect(Collectors.groupingBy(Function.identity(), Collectors.counting()));