I have two integer arrays e.g. -
int[] a = {2, 7, 9}
int[] b = {4, 2, 8}
I want to compare it element by element i.e. 2 to 4 then 7 to 2 and finally 9 to 8. Each comparison result will be stored in a list.
This is pretty easy to do in the traditional Java ways. But I want to use Stream here. Any pointers?
You may do it like so,
List<Boolean> equalityResult = IntStream.range(0, a.length).mapToObj(i -> a[i] == b[i])
.collect(Collectors.toList());
Precondition: both the arrays are of same size.
Assuming the length of both the input arrays are same
List<Integer> list = IntStream.range(0, a.length).mapToObj(i -> Integer.compare(a[i], b[i]))
.collect(Collectors.toCollection(() -> new ArrayList<>(a.length)));
toList() instead of toCollection(...)
() -> new ArrayList<>(a.length) can be of any good than Supplier<List<T>>) ArrayList::new (default capacity maybe!) with this Collectors implementation?
ArrayList with the number of expected elements might be good for a sequential stream, but cause oversized temporary arrays with a parallel stream. Today, the best solution would be List<Integer> list = Arrays.asList( /* your stream operation */ .toArray(Integer[]::new));, as this will utilize the known number of elements, even in the parallel case, letting all threads write into the one final array, when the sizes are predictable, like in this specific case. But don’t try to optimize when there is no performance problem.Same as other answers with a bit difference
List<Integer> result = IntStream.rangeClosed(0,a.length-1)
.boxed()
.map(i->Integer.compare(a[i],b[i]))
.collect(Collectors.toList());
.mapToObj instead of .boxed().maprange(0, a.length) instead of rangeClosed(0, a.length-1)You're essentially looking for the functionality of a Zip operation (which is not available in Java yet).
To get a set of booleans, as a result, I would recommend:
boolean[] accumulator = new boolean[a.length];
IntStream.range(0, a.length)
.forEachOrdered(i -> accumulator[i] = a[i] == b[i]);
and respectively to get the result as an int between corresponding elements in both arrays:
int[] ints = IntStream.range(0, a.length)
.map(i -> Integer.compare(a[i], b[i]))
.toArray();
