How to efficiently search a string in an array of strings given a few conditions?

Question

I'm trying to filter an array of strings and return the strings that match based on two use cases.

Case 1: Only match if the searchString is at the beginning of the word.

For eg, if we have an array -> ["Ralph Breaks The Internet", "Bohemian Rhapsody", "Spider-Man: Into the Spider-Verse"] and we are trying to match it with a search string "r"

In this case, we should return ["Ralph Breaks The Internet", "Bohemian Rhapsody"] as "r" is at the beginning as in r in ralph and r in rhapsody. But "Spider-Man: Into the Spider-Verse" is not matched as the r is in the middle.

Case 2: Also match if the order of searchText is not exact.

For eg, if we have an array -> ["Ralph Breaks The Internet", "Bohemian Rhapsody", "Spider-Man: Into the Spider-Verse"] and we are trying to match it with a search string "Rhapsody Bohemian", it should still match even though the order is not the same.

Here's what I have tried so far:

func searchMovies(_ movieNames: [String], with searchText: String) -> [String] {
    
    var matchedMovies = [String]()
    
    for movie in movieNames {
        
        let movieWords = movie.split(separator: " ")
        let searchTextWords = searchText.split(separator: " ")
        var count = searchTextWords.count
        
        loop:
        for word in movieWords {
            for text in searchTextWords {
                let pattern = "\\b\(text)"
                if let _ = word.range(of: pattern, options: [.regularExpression, .caseInsensitive]) {
                    count -= 1
                }
                if count == 0 {
                    matchedMovies.append(movie)
                    break loop
                }
            }
        }
    }
    
    return matchedMovies
}

I'm aware this is not an efficient way to do this. It would be great if someone can direct me in some direction so that I can solve the same thing more efficiently.

DonMag · Accepted Answer · 2021-04-27 16:26:57Z

1

For your specific case, you can format your regex pattern like this:

"^(?=.*\\bRhapsody)(?=.*\\bBohemian).*$"

To make it flexible, you could write your func like this:

func searchMovies(_ movieNames: [String], with searchText: String) -> [String] {
    // split search text into "words"
    let words: [String] = searchText.components(separatedBy: " ")
    
    // start of pattern string
    var pattern: String = "^"
    
    // for each word in search text
    words.forEach { w in
        // append regex to search for words beginning with word
        pattern += "(?=.*\\b\(w))"
    }
    
    // end of pattern string
    pattern += ".*$"
    
    return movieNames.filter { (movie) -> Bool in
        if let _ = movie.range(of: pattern, options: [.regularExpression, .caseInsensitive]) {
            return true
        }
        return false
    }
}

And you can call it with:

    let a: [String] = [
        "Ralph Breaks The Internet",
        "Bohemian Rhapsody",
        "Spider-Man: Into the Spider-Verse"
    ]
    
    let matchingArray = searchMovies(a, with: "Rhapsody Bohemian")

Note that this will match the beginning of the word (as you showed using "r"), so this will return the same result:

let matchingArray = searchMovies(a, with: "Rhap Boh")

answered Apr 27, 2021 at 16:26

DonMag

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4 Comments

Ameya Vichare Over a year ago

Thank you, it works very well. Could you explain what "^(?=.*\\bRhapsody)(?=.*\\bBohemian).*$" exactly does?

DonMag Over a year ago

Go to this link: regex101.com/r/J38aas/1 ... it will show you a detailed explanation of that regex pattern.

Larme Over a year ago

@AmeyaVichare Copy/paste it in a Regex Online (remove the double backslash that's Swift specific), and you should get an idea.

Ameya Vichare Over a year ago

Thanks @DonMag and Larme

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