Java reduces the collection of strings to the mapping that occurs

Treat list as Id1_ f,id2_ d,id3_ f,id1_ g. How do I use streams to obtain simplified mappings of statistics in the format < string, integer >

id1 2
id2 1
id3 1

Note: the key is_ It was part of the Can reduced functionality help?

Solution

This will complete the work:

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