Is there a zip function to create tuples with more than 2 elements?

Question

I just discovered the Swift zip function recently. It seems quite useful.

It takes 2 input arrays and creates an array of tuples out of pairs of values from each array.

Is there a variant of zip that takes an arbitrary number of arrays and outputs tuples with that same number of elements? It seems like there should be a way to do this.

I'm no expert at Swift but while you can create a function that takes a variable number of sequence parameters, how would you declare the return type to be a tuple of unknown size? — rmaddy, Nov 09 '16 at 23:45
Good point. You can use generics to define the function to create tuples who's elements are the types of the input array elements, but I don't know of a way in Swift to define a tuple of variable size. — Duncan C, Nov 09 '16 at 23:49

score 19 · Answer 1 · answered Nov 11 '16 at 03:31

19

Bear in mind, you can nest one zip inside another, and then unpack it with a nested tuple:

let integers = [1, 2, 3, 4, 5]
let strings = ["a", "b", "c", "d", "e"]
let doubles = [1.0, 2.0, 3.0, 4.0, 5.0]

for (integer, (string, double)) in zip(integers, zip(strings, doubles)) {
    print("\(integer) \(string) \(double)")
}

Not quite as elegant as having a zip for arbitrary n-tuples, but it gets the job done.

answered Nov 11 '16 at 03:31

Airspeed Velocity

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You are a genius. – DawnSong May 09 '17 at 03:32
i am getting error of `extra argument in call` i am doing exactly what you are doing, whats error in my code? – iOS Developer Aug 07 '18 at 07:05
Much better than the accepted answer - no need to fight Swift's standard library for only one nested tuple. – Pranav Kasetti Mar 11 '21 at 02:07

score 11 · Accepted Answer · edited Jun 20 '20 at 09:12

11

No, zip for an arbitrary number of sequences isn't currently possible due to Swift's lack of variadic generics. This is discussed in the Generics Manifesto.

In the meanwhile, I wrote a gyb template for generating ZipSequences of custom arity. I've also pre-generated ZipSequences of arity 3...10 for your convenience. It's available here.

In action:

let integers = [1, 2, 3, 4, 5]
let strings = ["a", "b", "c", "d", "e"]
let doubles = [1.0, 2.0, 3.0, 4.0, 5.0]

for (integer, string, double) in zip(integers, strings, doubles) {
    print("\(integer) \(string) \(double)")
}

Prints:

1 a 1.0

2 b 2.0

3 c 3.0

4 d 4.0

5 e 5.0

edited Jun 20 '20 at 09:12

Community

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answered Nov 10 '16 at 01:07

Alexander

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Thanks for the conclusive answer and the link to the Generics Manifesto. – Duncan C Nov 10 '16 at 01:18
You can write your own zip3 or such, based off the source: https://github.com/apple/swift/blob/master/stdlib/public/core/Zip.swift – Alexander Nov 10 '16 at 01:21
@Alexander i am getting error of `extra argument in call` i am doing exactly what you are doing, whats error in my code? – iOS Developer Aug 07 '18 at 07:05
should i import something or just add the sequecs – iOS Developer Aug 07 '18 at 07:31
1

@iOSDeveloper You just copy the source file into your project. I haven't bothered to make it into a standalone library or framework, or anything like that – Alexander Aug 07 '18 at 16:08

score 0 · Answer 3 · answered Nov 14 '19 at 09:44

You can use the nested zip approach as in some of the previous answers, and use map to flatten the result:

let combined = zip(integers, zip(strings, doubles)).map { ( $0.0, $0.1.0, $0.1.1 ) }

It yields an array of tuples, each with three elements. Looks a bit ugly but as long as it works… It does work as long as the number of arrays to zip is fixed.

Is there a zip function to create tuples with more than 2 elements?

3 Answers3

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