Given a stream such as { 0, 1, 2, 3, 4 },
how can I most elegantly transform it into given form:
{ new Pair(0, 1), new Pair(1, 2), new Pair(2, 3), new Pair(3, 4) }
(assuming, of course, I’ve defined class Pair)?
Edit: This isn’t strictly about ints or primitive streams. The answer should be general for a stream of any type.
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Answer
My StreamEx library which extends standard streams provides a pairMap method for all stream types. For primitive streams it does not change the stream type, but can be used to make some calculations. Most common usage is to calculate differences:
int[] pairwiseDiffs = IntStreamEx.of(input).pairMap((a, b) -> (b-a)).toArray();
For object stream you can create any other object type. My library does not provide any new user-visible data structures like Pair (that’s the part of library concept). However if you have your own Pair class and want to use it, you can do the following:
Stream<Pair> pairs = IntStreamEx.of(input).boxed().pairMap(Pair::new);
Or if you already have some Stream:
Stream<Pair> pairs = StreamEx.of(stream).pairMap(Pair::new);
This functionality is implemented using custom spliterator. It has quite low overhead and can parallelize nicely. Of course it works with any stream source, not just random access list/array like many other solutions. In many tests it performs really well. Here’s a JMH benchmark where we find all input values preceding a larger value using different approaches (see this question).