How to sum an array of numbers using reduce()

Swift version: 5.1

Paul Hudson    @twostraws    May 28th 2019

The reduce() method is designed to convert a sequence into a single value, which makes it perfect for calculating the total of an array of numbers.

For example, given the following number array:

let numbers = [1, 12, 2, 9, 27]

We could calculate the total of all those numbers like this:

let total = numbers.reduce(0, +)

The first parameter passed to reduce() is the value it should start with, in this case 0. The second parameter is how it should combine that 0 with each item in your array, which means it will do 0 + 1 to make 1, then 1 + 12 to make 13, and so on.

Available from iOS 8.0

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