Swift 3 simple search engine - arrays

Question

I have an array of Strings containing user inputted values. I have a string containing several words (the number of words in the string varies). I want to increment an Int every time one of the words in the string matches a word in the array.
I'm using this method:
var searchWordsArr: [String] = [] \\filled by user input
var message: String = "" \\random number of words
var numRelevantWords = 0
var i = 0
while i < self.searchWordsArr.count {
i+=1
if message.contains(self.searchWordsArr[i-1]) {
numRelevantWords += 1
}
}
In my first example, the string contained 25 words and the array contained 3 words. The 3 words came up a total of 12 times in the string. Using the above method, the value of numRelevantWords was 2.

Answer 1

I would use regex. Some day soon, Swift will have native regular expressions. But until it does, you have to resort to Foundation:
let words = ["the", "cat", "sat"]
let input = "The cat sat on the mat and the mat sat on the catastrophe"
var result = 0
let pattern = "\\b(" + words.joined(separator:"|") + ")\\b"
do {
let regex = try NSRegularExpression(pattern: pattern, options: .caseInsensitive)
let match = regex.matches(in: input, options: [], range: NSRange(location: 0, length: input.utf16.count))
result += match.count // 7, that's your answer
} catch {
print("illegal regex")
}

Answer 2

Add them to a NSCountedSet:
let searchWords = NSCountedSet()
searchWords.add("Bob")
searchWords.add("John")
searchWords.add("Bob")
print(searchWords.count(for: "Bob")) // 2

Answer 3

"pure" Swift (no Foundation)
let message = "aa bb aaaa ab ac aa aa"
let words = message.characters.split(separator: " ").map(String.init)
let search:Set = ["aa", "bb", "aa"]
let found = words.reduce(0) { (i, word) -> Int in
var i = i
i += search.contains(word) ? 1 : 0
return i
}
print(found, "word(s) from the message are in the search set")
prints
4 word(s) from the the message are in the search set
UPDATE (see discussion)
using Set
var search: Set<String> = [] // an empty set with Element == String
search.insert("aa") // insert word to set
using Array
var search: Array<String> = [] // an empty array
search.append("aa") // append word to array
maybe you are looking for
let message = "the cat in the hat"
let words = message.characters.split(separator: " ").map(String.init)
let search:Set = ["aa", "bb", "pppp", "the"]
let found = search.reduce(0) { (i, word) -> Int in
var i = i
i += words.contains(word) ? 1 : 0
return i
}
print(found, "word(s) from the search set found in the message")
prints
1 word(s) from the search set found in the message
if you would like to produce the same as with accepted answer
let words = ["the", "cat", "sat"]
let input = "The cat sat on the mat and the mat sat on the catastrophe"
let inputWords = input.lowercased().characters.split(separator: " ").map(String.init)
let found = inputWords.reduce(0) { (i, word) -> Int in
var i = i
i += words.contains(word.lowercased()) ? 1 : 0
return i
}
print(found, "word(s) from the search set found in the message")
prints
7 word(s) from the search set found in the message