Filter out element one by one using filter()

Joka Lee :

I will kick start with my question:

I have an array:

int[] arr = { 1,2,3,4,5 }; , i want to store values to a List<Integer> li like this : 14,13,12,11,10

How these values came to the List li like this??

Our initial numbers are 1,2 ,3 ,4 , and 5 . We can calculate the following sums using four of the five integers:

• If we sum everything except 1, our sum is 14.
• If we sum everything except 2, our sum is 13.
• If we sum everything except 3, our sum is 12.
• If we sum everything except 4, our sum is 11.
• If we sum everything except 5, our sum is 10.

My approach and thoughts:

I thought i already have an int [] arr , so i will make it to stream , now i will filter out each elements one by one and will sum rest in each iteration and will add this to List li.

List<Integer> li   = IntStream.range(0,1).filter(i-> arr[i] !=i).sum();

^^ This did not worked, I am thinking can i do some this like below?

IntStream.range(0,1).filter(i-> filter(this is anotherfilter)).sum();

I am not able to understand this, i want to do this problem with streams and java-8.

Naman :

You can break it into two steps and perform the operation as:

int[] arr = { 1,2,3,4,5 };
int total = Arrays.stream(arr).sum(); // total of the array
List<Integer> output = Arrays.stream(arr)
        .mapToObj(integer -> total - integer) // (total - current) value as element
        .collect(Collectors.toList());