amaembo
commented
6 months ago Yes, it's expected. As [javadoc](https://www.javadoc.io/doc/one.util/streamex/latest/one.util.streamex/one/util/streamex/EntryStream.html#collapseKeys()) says, collapse "Merge series of adjacent stream entries with equal keys".
The easiest way to solve your problem is to use grouping():
Map<String, List<Integer>> map =
EntryStream.of("1", 1, "2", 4, "1", 2).grouping();
Map<String,List> map1= EntryStream.of("1", 1,"2",4, "1", 2).sortedBy(Entry::getKey).collapseKeys().toMap();//works fine
System.out.println(map1); // {1=[1, 2], 2=[4]}
//Duplicate entry for key '1' (attempt to merge values '[1]' and '[2]') Map<String,List> map2= EntryStream.of("1", 1,"2",4, "1", 2).collapseKeys().toMap();
System.out.println(map2);
not sure this is feature or bug. thx