levenshtein-automata's Introduction

Levenshtein-automaton

This crate makes it fast and simple to build a finite determinic automaton that computes the levenshtein distance from a given string.

Example

use levenshtein_automata::{LevenshteinAutomatonBuilder, Distance};

fn main() {

    // Building this factory is not free.
    let lev_automaton_builder = LevenshteinAutomatonBuilder::new(2, true);

    // We can now build an entire dfa.
    let dfa = lev_automaton_builder.build_dfa("Levenshtein");

    let mut state = dfa.initial_state();
    for &b in "Levenshtain".as_bytes() {
        state = dfa.transition(state, b);
    }

    assert_eq!(dfa.distance(state), Distance::Exact(1));
}

The implementation is based on the following paper Fast String Correction with Levenshtein-Automata (2002) by by Klaus Schulz and Stoyan Mihov. I also tried to explain it in the following blog post.

Bench

The time taken by the construction a Levenshtein DFA strongly depends on the max distance it can measure and the length of the input string.

Here is the time spent to build a Levenshtein DFA for the string "Levenshtein"

dfa dist1 no transposition        35,627 ns/iter (+/- 3,237)
dfa dist1 with transposition      36,493 ns/iter (+/- 12,680)
dfa dist2 no transposition        97,137 ns/iter (+/- 14,556)
dfa dist2 with transposition     100,958 ns/iter (+/- 4,231)
dfa dist3 no transposition       834,412 ns/iter (+/- 158,329)
dfa dist3 with transposition   1,414,523 ns/iter (+/- 396,278)
dfa dist4 no transposition     4,716,365 ns/iter (+/- 869,024)
dfa dist4 with transposition   8,044,162 ns/iter (+/- 594,523)

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