您可以简单地从第一个集合中创建一个集合，并使其与另一个集合相交:

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"] 

请注意，结果集合的顺序是不可预测的.如果您想保留第一个集合的顺序，则可以创建第二个集合的集合并过滤无法插入其中的元素:

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"]

您还可以在RangeReplaceableCollection上创建自己的交集方法:

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 }
    }
}

用法:

Usage:

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