How can I flatten an array swiftily in Swift?

Question

I want to turn this:

let x = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]

into this:

[1, 2, 3, 4, 5, 6, 7, 8, 9]

ver

Answer 1

There's a built-in function for this called joined:

[[1, 2, 3], [4, 5, 6], [7, 8, 9]].joined()

(Note that this doesn't actually return another Array, it returns a FlattenSequence, but that usually doesn't matter because it's still a sequence that you can use with for loops and whatnot. If you really care, you can use Array(arrayOfArrays.joined()).)

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The flatMap function can also help you out. Its signature is, roughly,

flatMap(fn: (Generator.Element) -> S) -> [S.Generator.Element]

This means that you can pass a fn which for any element returns a sequence, and it'll combine/concatenate those sequences.

Since your array's elements are themselves sequences, you can use a function which just returns the element itself ({ x in return x } or equivalently just {$0}):

[[1, 2, 3], [4, 5, 6], [7, 8, 9]].flatMap{ $0 }