Swift: what is the right way to split up a [String] resulting in a [[String]] with a given subarray size?

Question

Starting with a large [String] and a given subarray size, what is the best way I could go about splitting up this array into smaller arrays? (The last array will be smaller than the given subarray size).

Concrete example:

Split up ["1","2","3","4","5","6","7"] with max split size 2

The code would produce [["1","2"],["3","4"],["5","6"],["7"]]

Obviously I could do this a little more manually, but I feel like in swift something like map() or reduce() may do what I want really beautifully.

Answer 1

In Swift 3/4 this would look like the following:

let numbers = ["1","2","3","4","5","6","7"] let chunkSize = 2 let chunks = stride(from: 0, to: numbers.count, by: chunkSize).map {     Array(numbers[$0..<min($0 + chunkSize, numbers.count)]) } // prints as [["1", "2"], ["3", "4"], ["5", "6"], ["7"]] 

As an extension to Array:

extension Array {     func chunked(by chunkSize: Int) -> [[Element]] {         return stride(from: 0, to: self.count, by: chunkSize).map {             Array(self[$0..<Swift.min($0 + chunkSize, self.count)])         }     } } 

Or the slightly more verbose, yet more general:

let numbers = ["1","2","3","4","5","6","7"] let chunkSize = 2 let chunks: [[String]] = stride(from: 0, to: numbers.count, by: chunkSize).map {     let end = numbers.endIndex     let chunkEnd = numbers.index($0, offsetBy: chunkSize, limitedBy: end) ?? end     return Array(numbers[$0..<chunkEnd]) } 

This is more general because I am making fewer assumptions about the type of the index into the collection. In the previous implementation I assumed that they could be could be compared and added.

Note that in Swift 3 the functionality of advancing indices has been transferred from the indices themselves to the collection.