[swift-evolution] Fast String Comparison From String Arrays

Huon Wilson huon at apple.com
Fri Jul 28 15:57:02 CDT 2017

> On Jul 28, 2017, at 05:54, Omar Charif via swift-evolution <swift-evolution at swift.org> wrote:
> Hi,
> I wonder whether there is already a way in Swift to compare a string against a large string array quickly without using the traditional ways of comparison. 
> Say we have ["a", "b", "c", "d"] and we would like to find whether this array contains "a", then we decide to check if we have "b" in that same array. Don't you think there is a way to represent the array in a different way and make this comparison a lot quicker ?
> I know there are recurrent neural networks etc ... I am talking here about solution without learning anything, just representing the array differently so we can minimize that O(N).
> I have developed an algorithm and it is doing pretty well so far and I wonder whether it would be accepted so I came to propose and see if this is interesting from your perspective.
> I developed a Javascript version here https://omarshariffathi.github.io/quickhint/ <https://omarshariffathi.github.io/quickhint/>
> If you think this is welcome in Swift Foundation I am ready for a pull request.
> Thanks for reading.
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If you’re doing only direct containment, the builtin Set will give O(1) lookups.

If you’re looking for, say, finding all values with a given prefix then a trie might be appropriate, and if you’re trying to do more interesting things (e.g. fuzzy search) there’s techniques like “finite state transducers” http://blog.burntsushi.net/transducers/ . I don’t believe either of these have anything built-in, and I suspect they (especially FSTs) are too specialized, or have too many possible variations, to be worth including directly in the current standard library, and a SwiftPM package would work almost as well as others have suggested.

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