Swift running sum

Question

I\'d like a function runningSum on an array of numbers a (or any ordered collection of addable things) that returns an array of the same length where each eleme

Answer 1

If you just want it to work for Int, you can use this:

func runningSum(array: [Int]) -> [Int] {
    return array.reduce([], combine: { (sums, element) in
        return sums + [element + (sums.last ?? 0)]
    })
}

If you want it to be generic over the element type, you have to do a lot of extra work declaring the various number types to conform to a custom protocol that provides a zero element, and (if you want it generic over both floating point and integer types) an addition operation, because Swift doesn't do that already. (A future version of Swift may fix this problem.)