Is there any possibility to convert a List of Set to Set using java 8 streams. Here my List :
// Get Header Columns to display in EXCEL FILE
List<Set<String>> keysQuery = listExtractQglobal.parallelStream()
.map(m -> m.keySet()).distinct().collect(Collectors.toList());
Thanks
Just use a flatMap
Set<String> a = keysQuery.stream().flatMap(s -> s.stream()).collect(Collectors.toSet());
As the comment indicated you can also replace the lambda function with lambda reference
Set<String> a = keysQuery.stream().flatMap(Set::stream).collect(Collectors.toSet());
.flatMap(Set::stream).Assuming this is how you create your list:
List<Set<String>> keysQuery = listExtractQglobal.parallelStream()
.map(m -> m.keySet()).distinct().collect(Collectors.toList());
you can actually avoid unnecessary collecting to a list and collect to a set instead:
Set<String> keysQuery = listExtractQglobal.parallelStream()
.map(Map::keySet)
.distinct()
.flatMap(Collection::stream)
.collect(Collectors.toSet());
Btw, I'm not sure why do you need the distinct here. Are you looking for distinct sets or distinct keys among all key sets? In latter case you could simply omit the distinct(), since the resulting Set contains distinct values by definition:
Set<String> keysQuery = listExtractQglobal.parallelStream()
.map(Map::keySet)
.flatMap(Collection::stream)
.collect(Collectors.toSet());
I would use Stream#mapMulti from java-16 instead of Stream#flatMap as it has an overhead of possibly creating empty or very small streams
Set<String> keysQuery = listExtractQglobal.parallelStream()
.map(Map::keySet)
.mapMulti((Set<String> set, Consumer<String> consumer) -> {
set.forEach(consumer::accept);
})
.collect(Collectors.toSet());
listExtractQglobalvariable?