Swift - How to get indexes of filtered items of array

Question

let items: [String] = [\"A\", \"B\", \"A\", \"C\", \"A\", \"D\"]

items.whatFunction(\"A\") // -> [0, 2, 4]
items.whatFunction(\"B\") // -> [1]

Answer 1

For example finding the indices of p_last values that are in inds1 array: (swift 4+)

let p_last = [51,42]
let inds1 = [1,3,51,42,4]
let idx1 = Array(inds1.filter{ p_last.contains($0) }.indices)

idx1 = [0,1]