Alexander Momchliov Alexander Momchliov - 5 days ago 6
Swift Question

Swift: What's the best way to pair up elements of an Array

I came across a problem that required iterating over an array in pairs. What's the best way to do this? Or, as an alternative, what's the best way of transforming an Array into an Array of pairs (which could then be iterated normally)?

Here's the best I got. It requires

output
to be a
var
, and it's not really pretty. Is there a better way?

let input = [1, 2, 3, 4, 5, 6]

var output = [(Int, Int)]()

for i in stride(from: 0, to: input.count - 1, by: 2) {
output.append((input[i], input[i+1]))
}


print(output) // [(1, 2), (3, 4), (5, 6)]

// let desiredOutput = [(1, 2), (3, 4), (5, 6)]
// print(desiredOutput)

Answer

You can map the stride instead of iterating it, that allows to get the result as a constant:

let input = [1, 2, 3, 4, 5, 6]

let output = stride(from: 0, to: input.count - 1, by: 2).map {
    (input[$0], input[$0+1])
}

print(output) // [(1, 2), (3, 4), (5, 6)]

If you only need to iterate over the pairs and the given array is large then it may be advantageous to avoid the creation of an intermediate array with a lazy mapping:

for (left, right) in stride(from: 0, to: input.count - 1, by: 2)
    .lazy
    .map( { (input[$0], input[$0+1]) } ) {

    print(left, right)

}
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