How to reverse array in Swift without using “.reverse()”?

Question

I have array and need to reverse it without Array.reverse method, only with a for loop.

var names:[String] = [\"Apple\", \"Microsof         


        

Answer 1

Only need to make (names.count/2) passes through the array. No need to declare temporary variable, when doing the swap...it's implicit.

var names:[String] = ["Apple", "Microsoft", "Sony", "Lenovo", "Asus"]
let count = names.count
for i in 0..<count/2 {
   (names[i],names[count - i - 1])  = (names[count - i - 1],names[i])
}
// Yields: ["Asus", "Lenovo", "Sony", "Microsoft", "Apple"]

Answer 2

Swift 3:

var names:[String] = ["Apple", "Microsoft", "Sony", "Lenovo", "Asus"]

var reversedNames : [String] = Array(names.reversed())

print(reversedNames)  // ["Asus", "Lenovo", "Sony", "Microsoft", "Apple"]

Answer 3

var arr = [1, 2, 3, 4, 5]   // Array we want to reverse
var reverse: [Int]!      // Array where we store reversed values

reverse = arr

for i in 0...(arr.count - 1) {

    reverse[i] = arr.last!  // Adding last value of original array at reverse[0]
    arr.removeLast()        // removing last value & repeating above step.
}

print("Reverse : \(reverse!)")

A more simple way :)

Answer 4

There's also stride to generate a reversed index:

let names = ["Apple", "Microsoft", "Sony", "Lenovo", "Asus"]

var reversed = [String]()

for index in (names.count - 1).stride(to: -1, by: -1) {
    reversed.append(names[index])
}

It also works well with map:

let reversed = (names.count - 1).stride(to: -1, by: -1).map { names[$0] }

Note: stride starts its index at 1, not at 0, contrary to other Swift sequences.

However, to anyone reading this in the future: use .reverse() instead to actually reverse an array, it's the intended way.

Answer 5

Do it like this for reversed sorting.

 let unsortedArray: [String] = ["X", "B", "M", "P", "Z"]
        // reverse sorting
        let reversedArray = unsortedArray.sorted() {$0 > $1}

        print(reversedArray) // ["Z", "X", "P", "M", "B"]

Answer 6

Here is @Abhinav 's answer translated to Swift 2.2 :

var names: [String] = ["Apple", "Microsoft", "Sony", "Lenovo", "Asus"]

var reversedNames = [String]()

for arrayIndex in (names.count - 1).stride(through: 0, by: -1) {
    reversedNames.append(names[arrayIndex])
}

Using this code shouldn't give you any errors or warnings about the use deprecated of C-style for-loops or the use of --.

Swift 3 - Current:

let names: [String] = ["Apple", "Microsoft", "Sony", "Lenovo", "Asus"]

var reversedNames = [String]()

for arrayIndex in stride(from: names.count - 1, through: 0, by: -1) {
    reversedNames.append(names[arrayIndex])
}

Alternatively, you could loop through normally and subtract each time:

let names = ["Apple", "Microsoft", "Sony", "Lenovo", "Asus"]

let totalIndices = names.count - 1 // We get this value one time instead of once per iteration.

var reversedNames = [String]()

for arrayIndex in 0...totalIndices {
    reversedNames.append(names[totalIndices - arrayIndex])
}