Simple way to check for membership in a list? - swift2

Question

For use in a closure (though I suppose it will be useful elsewhere as well), what is the cleanest way to check to see whether or not a given element is a member of a list (or any character is a member of a string)?
For example, to check whether or not the string "abcde" contains any of the characters in "aeiou", or whether the list ["bill", "sam" , "suzy"] contains any of the names in ["abe", "bill", "charlie"]?

Answer 1

1 ) Common chars in 2 words
You easily check the intersection of the common chars in 2 strings using the Set struct:
let set0 = Set("abcde".characters)
let set1 = Set("aeiou".characters)
let intersection = set0.intersect(set1) // {"e", "a"}
2) Common words in 2 lists
Similarly you can find the intersection of 2 arrays of strings:
let set0 : Set = ["bill", "sam", "suzy"]
let set1 : Set = ["abe", "bill", "charlie"]
let intersection = set0.intersect(set1) // {"bill"}
3) Back to Array
Please note that in both examples, the intersection constant is a Set. You can transform it into an Array writing:
let list = Array(intersection)
Hope this helps.
P.S. This code is for Swift 2.0
Update
More specifically if you want to find out whether an intersection exists you can simply write:
!intersection.isEmpty

Answer 2

Swift arrays have built in functions for this exact functionality.
I recommend checking out the official documentation for Collection Types from Apple for a starting point.
Here is an example that follows your question:
// With [Character]
let vowels: [Character] = ["a", "e", "i", "o", "u"]
let chars: [Character] = ["a", "b", "c", "d", "e"]
let resultVowels = vowels.filter { chars.contains($0) }
resultVowels.count // == 2
resultVowels.description // == "[a, e]"
// With [String]
let people = ["Bill", "Sam", "Suzy"]
let peeps = ["Abe", "Bill", "Charlie"]
let resultPeople = people.filter { peeps.contains($0) }
resultPeople.count // == 1
resultPeople.description // == "[Bill]"
The result will be the names (or numbers, characters, etc.) that are matching up. So you can not only get the count, but also the contents of the comparison in this procedure. So long as the types follow Equatable, this will work for you.
If you want to return a Boolean, just simply:
return filteredArray.count != 0
Now, if you want to compare say, a [Character] to a String then:
let vowels: [Character] = ["a", "e", "i", "o", "u"]
let someString = "abcde"
let result = vowels.filter { someString.characters.contains($0) }
result.count // == 2
result.description // == "[a, e]"
The String.characters property is a new feature brought in to Swift 2.
I hope I was able to assist you.