How to find index of list item in Swift?

Question

I am trying to find an item index by searching a list. Does anybody know how to do that?

I see there is list.StartIndex and <

Answer 1

You can filter an array with a closure:

var myList = [1, 2, 3, 4]
var filtered = myList.filter { $0 == 3 }  // <= returns [3]

And you can count an array:

filtered.count // <= returns 1

So you can determine if an array includes your element by combining these:

myList.filter { $0 == 3 }.count > 0  // <= returns true if the array includes 3

If you want to find the position, I don't see fancy way, but you can certainly do it like this:

var found: Int?  // <= will hold the index if it was found, or else will be nil
for i in (0..x.count) {
    if x[i] == 3 {
        found = i
    }
}

EDIT

While we're at it, for a fun exercise let's extend Array to have a find method:

extension Array {
    func find(includedElement: T -> Bool) -> Int? {
        for (idx, element) in enumerate(self) {
            if includedElement(element) {
                return idx
            }
        }
        return nil
    }
}

Now we can do this:

myList.find { $0 == 3 }
// returns the index position of 3 or nil if not found

Answer 2

Swift 5

func firstIndex(of element: Element) -> Int?

var alphabets = ["A", "B", "E", "D"]

Example1

let index = alphabets.firstIndex(where: {$0 == "A"})

Example2

if let i = alphabets.firstIndex(of: "E") {
    alphabets[i] = "C" // i is the index
}
print(alphabets)
// Prints "["A", "B", "C", "D"]"

Answer 3

In Swift 4, if you are traversing through your DataModel array, make sure your data model conforms to Equatable Protocol , implement the lhs=rhs method , and only then you can use ".index(of" . For example

class Photo : Equatable{
    var imageURL: URL?
    init(imageURL: URL){
        self.imageURL = imageURL
    }

    static func == (lhs: Photo, rhs: Photo) -> Bool{
        return lhs.imageURL == rhs.imageURL
    }
}

And then,

let index = self.photos.index(of: aPhoto)

Answer 4

SWIFT 4

Let's say you want to store a number from the array called cardButtons into cardNumber, you can do it this way:

let cardNumber = cardButtons.index(of: sender)

sender is the name of your button