How to return first 5 objects of Array in Swift?

Question

In Swift, is there a clever way of using the higher order methods on Array to return the 5 first objects? The obj-c way of doing it was saving an index, and for-loop throug

Answer 1

SWIFT 4

A different solution:

An easy inline solution that wont crash if your array is too short

[0,1,2,3,4,5].enumerated().compactMap{ $0.offset < 3 ? $0.element : nil }

But works fine with this.

[0,1,2,3,4,5].enumerated().compactMap{ $0.offset < 1000 ? $0.element : nil }

Usually this would crash if you did this:

[0,1,2,3,4,5].prefix(upTo: 1000) // THIS CRASHES

[0,1,2,3,4,5].prefix(1000) // THIS DOESNT

Answer 2

I slightly changed Markus' answer to update it for the latest Swift version, as var inside your method declaration is no longer supported:

extension Array {
    func takeElements(elementCount: Int) -> Array {
        if (elementCount > count) {
            return Array(self[0..<count])
        }
        return Array(self[0..<elementCount])
    }
}

Answer 3

Update: There is now the possibility to use prefix to get the first n elements of an array. Check @mluisbrown's answer for an explanation how to use prefix.

Original Answer: You can do it really easy without filter, map or reduce by just returning a range of your array:

var wholeArray = [1, 2, 3, 4, 5, 6]
var n = 5

var firstFive = wholeArray[0..<n] // 1,2,3,4,5

Answer 4

For getting the first 5 elements of an array, all you need to do is slice the array in question. In Swift, you do it like this: array[0..<5].

To make picking the N first elements of an array a bit more functional and generalizable, you could create an extension method for doing it. For instance:

extension Array {
    func takeElements(var elementCount: Int) -> Array {
        if (elementCount > count) {
            elementCount = count
        }
        return Array(self[0..<elementCount])
    }
}

Answer 5

For an array of objects you can create an extension from Sequence.

extension Sequence {
    func limit(_ max: Int) -> [Element] {
        return self.enumerated()
            .filter { $0.offset < max }
            .map { $0.element }
    }
}

Usage:

struct Apple {}

let apples: [Apple] = [Apple(), Apple(), Apple()]
let limitTwoApples = apples.limit(2)

// limitTwoApples: [Apple(), Apple()]

Answer 6

By far the neatest way to get the first N elements of a Swift array is using prefix(_ maxLength: Int):

let someArray = [1, 2, 3, 4, 5, 6, 7]
let first5 = someArray.prefix(5) // 1, 2, 3, 4, 5

This has the benefit of being bounds safe. If the count you pass to prefix is larger than the array count then it just returns the whole array.

NOTE: as pointed out in the comments, Array.prefix actually returns an ArraySlice, not an Array. In most cases this shouldn't make a difference but if you need to assign the result to an Array type or pass it to a method that's expecting an Array param you will need to force the result into an Array type: let first5 = Array(someArray.prefix(5))