Swift sum numbers in array adding from specific element

Question

Let's say I have some numbers in an array like below

let numberArray = [1, 3, 4, 6, 9, 14, 16]

I know how to sum them all up by using reduce method but how can I start adding numbers from specific element. For example:

//Sum all up by reduce
let sumAll = numberArray.reduce(0, +)
//sumAll = 53 

//I want to start counting from the fourth element in the array which is 6
//so the total should be 45. [6 + 9 + 14 + 16]

What method should I use to achieve this?
Thanks in advance.

vacawama · Accepted Answer · 2018-11-27 04:24:59Z

8

You can either use dropFirst(_:) or use a range as the index.

If it's not a fixed number, you could first use firstIndex(of:) to determine the index where you want to start.

numberArray.dropFirst(3).reduce(0, +)
numberArray[3...].reduce(0, +)

edited Nov 27, 2018 at 4:24

vacawama

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answered Nov 27, 2018 at 3:04

EmilioPelaez

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1 Comment

vacawama Over a year ago

dropFirst(3) is safer; it doesn't crash if numberArray has fewer than 3 elements.

rmaddy · Accepted Answer · 2018-11-27 03:04:12Z

4

Run reduce on the desired subarray:

let numberArray = [1, 3, 4, 6, 9, 14, 16]
let sum = numberArray[3...].reduce(0, +)

answered Nov 27, 2018 at 3:04

rmaddy

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