Java count occurrence of each item in an array

Question

Is there any method for counting the occurrence of each item on an array?

Lets say I have:

String[] array = {"name1","name2","name3","name4", "name5"}; 

Here the output will be:

name1 1 name2 1 name3 1 name4 1 name5 1 

and if I have:

String[] array = {"name1","name1","name2","name2", "name2"}; 

The output would be:

name1 2 name2 3 

The output here is just to demonstrate the expected result.

Answer 1

List asList = Arrays.asList(array); Set<String> mySet = new HashSet<String>(asList);  for(String s: mySet){  System.out.println(s + " " + Collections.frequency(asList,s)); } 

Answer 2

With java-8, you can do it like this:

String[] array = {"name1","name2","name3","name4", "name5", "name2"}; Arrays.stream(array)       .collect(Collectors.groupingBy(s -> s))       .forEach((k, v) -> System.out.println(k+" "+v.size())); 

Output:

name5 1 name4 1 name3 1 name2 2 name1 1 

What it does is:

• Create a Stream<String> from the original array
• Group each element by identity, resulting in a Map<String, List<String>>
• For each key value pair, print the key and the size of the list

If you want to get a Map that contains the number of occurences for each word, it can be done doing:

Map<String, Long> map = Arrays.stream(array)     .collect(Collectors.groupingBy(s -> s, Collectors.counting())); 

For more informations:

• Stream
• Collectors

Hope it helps! :)