Swift: reference to array element by key

Question

I have written my own small function to find an element in an array using a key. But I'm sure there is a ready to use implementation in Swift to get it in one line. Any hint?

func objectAtKey(array: [T], key: String) -> T? {
    for element in array {
        if element.name == key {
            return element
        }
    }
    return nil
}

I also know function indexOf, but this return an index, I have to use for further access. I think this is slower:

let index = array.indexOf({$0.name == key})

Martin R · Accepted Answer · 2016-08-30 20:30:14Z

4

In Swift 3 (Xcode 8, currently beta 6) you can do

if let el = array.first(where: { $0.name == key }) {
    // `el` is the first array element satisfying the condition.
    // ...
} else {
    // No array element satisfies the condition.
}

using the first(where:) method of the Sequence protocol:

/// Returns the first element of the sequence that satisfies the given
/// predicate or nil if no such element is found.
///
/// - Parameter predicate: A closure that takes an element of the
///   sequence as its argument and returns a Boolean value indicating
///   whether the element is a match.
/// - Returns: The first match or `nil` if there was no match.
public func first(where predicate: (Element) throws -> Bool) rethrows -> Element?

answered Aug 30, 2016 at 20:30

Martin R

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Comments

Rashwan L · Accepted Answer · 2016-08-30 20:19:47Z

1

I think the best solution for you here is to use the indexOf with a Predicate that you have written. I would have written it like this though:

let array = ["Foo", "Bar", "Test"]
if let i = array.indexOf({$0 == "Foo"}) {
     print(array[i])
}

To handle if the value does not exists if you need that.

answered Aug 30, 2016 at 20:19

Rashwan L

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Comments

Marco Santarossa · Accepted Answer · 2016-08-30 20:14:26Z

0

Try this:

let element = array.filter{ $0.name == key }.first

answered Aug 30, 2016 at 20:14

Marco Santarossa

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3 Comments

Peter71 Over a year ago

Yes, but this handles the entire array and takes the first element after doing all the work. I simply need the first (and only) matching element.

Hamish Over a year ago

This unnecessarily iterates through every element – a better (pre Swift 3) solution would be to take advantage of a lazy collection instead, e.g let element = array.lazy.filter{ $0.name == key }.first – allowing it to stop iterating upon finding a match.

Peter71 Over a year ago

That sounds perfect. Thank you.

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