Java reduce a collection of string to a map of occurence

Java reduce a collection of string to a map of occurence

Consider the a list as id1_f, id2_d, id3_f, id1_g, how can I use stream to get a reduced map in format of <String, Integer>of statistics like:

id1_f, id2_d, id3_f, id1_g

<String, Integer>

id1 2 id2 1 id3 1

Note: the key is part before _. Is reduce function can help here?

_

reduce

1 Answer
1

This will get the job done:

Map<String, Long> map = Stream.of("id1_f", "id2_d", "id3_f", "id1_g") .collect( Collectors.groupingBy(v -> v.substring(0, v.indexOf("_")), Collectors.counting()) );

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