Java reduce a collection of string to a map of occurence

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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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