Map Swift array with specific format

Question

Given an array that contains elements like this:

let array = [[a], [b, c], [d, e, f]]

Is there an elegant way to convert this array to an array which returns a tuple with the index of the outer array:

let result = [(a, 0), (b, 1), (c, 1), (d, 2), (e, 2), (f, 2)]

Answer 1

let array = [["a"], ["b", "c"], ["d", "e", "f"]]
let result = zip(array, array.indices).flatMap { subarray, index in
    subarray.map { ($0, index) }
}

result is:

[("a", 0), ("b", 1), ("c", 1), ("d", 2), ("e", 2), ("f", 2)]

I used zip(array, array.indices) instead of array.enumerated() because you specifically asked for a tuple with the array index — enumerated() produces tuples with zero-based integer offsets. If your source collection is an array, it doesn't make a difference, but other collections (like ArraySlice) would behave differently.