I have a list of objects. I want to do the following
for (int i = 0; i < sorted.size(); i++) {
map.put(i, sorted.get(i).getName());
}
Is there a straightforward way to do this in Java 8 streams api ?
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2 Answers
You can do the following:
Map<Integer, String> map =
IntStream.range(0, sorted.size())
.boxed()
.collect(toMap(i -> i, i -> sorted.get(i).getName()));
This creates a Stream of int going from 0 to the size of list and collects each value into a Map.
3 Comments
dinesh707
Thank you for the answer, but i was hoping for something more like sorted.stream().blah(....)
Tunaki
You can't stream a list with its indexes, unfortunately, see this: stackoverflow.com/q/28989841/1743880
Tagir Valeev
@dinesh707,
EntryStream.of(sorted).mapValues(s -> s.getName()).toMap() using my free library if you really want not to think about indices. In general Tunaki solution is fine.Since you want to collect the elements into a data structure which intrinsically tracks the position as its size, you can do the operation using a custom collector:
Map<Integer, String> map=sorted.stream()
.map(x -> x.getName())
.collect(HashMap::new, (m,s) -> m.put(m.size(), s),
(a,b) -> { int off=a.size(); b.forEach((i,s) -> a.put(i+off, s));});
The trickiest part is the merge function which will be used in parallel processing only. It adds all elements of a map to its preceding map, but has to offset the keys by the number of preceding elements.
