Check if an array contains elements of another array in swift

Question

I need to check if an array contains at least one or more elements of another array and print them out in swift. This is my situation:

var array1 = ["user1&q         


        

Answer 1

You can simply create a set from your first collection and get its intersection with the other collection:

let array1 = ["user1", "user2", "user3", "user4"]
let array2 = ["user3", "user5", "user7", "user9", "user4"]
let intersection = Array(Set(array1).intersection(array2)) // ["user4", "user3"] 

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Note that the order of the resulting collection is unpredictable. If you would like to preserve the order of the first collection you can create a set of the second collection and filter the elements that cannot be inserted to it:

var set = Set(array2)
let intersection = array1.filter { !set.insert($0).inserted }  // ["user3", "user4"]

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You can also create your own intersection method on RangeReplaceableCollection:

extension RangeReplaceableCollection {
    func intersection<S: Sequence>(_ sequence: S) -> Self where S.Element == Element, Element: Hashable {
        var set = Set(sequence)
        return filter { !set.insert($0).inserted }
    }
}

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Usage:

let intersection = array1.intersection(array2)  // ["user3", "user4"]