ANDROID how to filter a list base on another list in kotlin/java?

You can do something like this following by using union operator

fun temp()
{
    val firstList = arrayListOf(1,2,3,4,5)
    val secondList = arrayListOf(1,3,5,6,7)
    val finalList = firstList.union(secondList)
    println("First list : ${firstList}")
    println("Second list : ${secondList}")
    println("Final list : ${finalList}")
}

InsecondList contains common elements 1,3 and 5 as the firstList, It was removed in the finalList. You can also use distinct operator according to your needs.

If I understand correctly, you want entries from both lists, but they must appear only once. I assume from your last statement that the order does not matter. In that case this would be perfect for a Set. A Set is a Collection, so you can iterate through all the elements just as, for example, with a List.

EDIT

Code snippets:

Integer[] a = {1,2,3};
Integer[] b = {2,3,4};

Set<Integer> s = new HashSet<>();

s.addAll(Arrays.asList(a));
s.addAll(Arrays.asList(b));

for (int i : s) {
    System.out.print(i + ", ");
}
System.out.println();

If your integers are already in a primitive array:

int[] c = {1,2,3};
int[] d = {2,3,4};

Set<Integer> S = new HashSet<>();

S.addAll(Arrays.asList(Arrays.stream(c).boxed().toArray(Integer[]::new)));
S.addAll(Arrays.asList(Arrays.stream(d).boxed().toArray(Integer[]::new)));

for (int i : S) {
    System.out.print(i + ", ");
}
System.out.println();

For both of these the output is:

1, 2, 3, 4,