136 lines
4.3 KiB
Rust
136 lines
4.3 KiB
Rust
use std::cmp;
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use crate::symbol::Symbol;
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/// Finds the Levenshtein distance between two strings
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pub fn lev_distance(a: &str, b: &str) -> usize {
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// cases which don't require further computation
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if a.is_empty() {
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return b.chars().count();
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} else if b.is_empty() {
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return a.chars().count();
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}
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let mut dcol: Vec<_> = (0..=b.len()).collect();
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let mut t_last = 0;
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for (i, sc) in a.chars().enumerate() {
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let mut current = i;
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dcol[0] = current + 1;
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for (j, tc) in b.chars().enumerate() {
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let next = dcol[j + 1];
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if sc == tc {
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dcol[j + 1] = current;
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} else {
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dcol[j + 1] = cmp::min(current, next);
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dcol[j + 1] = cmp::min(dcol[j + 1], dcol[j]) + 1;
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}
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current = next;
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t_last = j;
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}
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}
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dcol[t_last + 1]
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}
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/// Finds the best match for a given word in the given iterator
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///
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/// As a loose rule to avoid the obviously incorrect suggestions, it takes
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/// an optional limit for the maximum allowable edit distance, which defaults
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/// to one-third of the given word.
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///
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/// Besides Levenshtein, we use case insensitive comparison to improve accuracy on an edge case with
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/// a lower(upper)case letters mismatch.
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pub fn find_best_match_for_name<'a, T>(iter_names: T,
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lookup: &str,
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dist: Option<usize>) -> Option<Symbol>
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where T: Iterator<Item = &'a Symbol> {
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let max_dist = dist.map_or_else(|| cmp::max(lookup.len(), 3) / 3, |d| d);
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let (case_insensitive_match, levenstein_match) = iter_names
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.filter_map(|&name| {
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let dist = lev_distance(lookup, &name.as_str());
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if dist <= max_dist {
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Some((name, dist))
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} else {
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None
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}
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})
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// Here we are collecting the next structure:
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// (case_insensitive_match, (levenstein_match, levenstein_distance))
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.fold((None, None), |result, (candidate, dist)| {
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(
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if candidate.as_str().to_uppercase() == lookup.to_uppercase() {
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Some(candidate)
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} else {
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result.0
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},
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match result.1 {
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None => Some((candidate, dist)),
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Some((c, d)) => Some(if dist < d { (candidate, dist) } else { (c, d) })
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}
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)
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});
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if let Some(candidate) = case_insensitive_match {
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Some(candidate) // exact case insensitive match has a higher priority
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} else {
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if let Some((candidate, _)) = levenstein_match { Some(candidate) } else { None }
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}
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}
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#[test]
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fn test_lev_distance() {
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use std::char::{from_u32, MAX};
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// Test bytelength agnosticity
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for c in (0..MAX as u32)
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.filter_map(|i| from_u32(i))
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.map(|i| i.to_string()) {
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assert_eq!(lev_distance(&c[..], &c[..]), 0);
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}
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let a = "\nMäry häd ä little lämb\n\nLittle lämb\n";
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let b = "\nMary häd ä little lämb\n\nLittle lämb\n";
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let c = "Mary häd ä little lämb\n\nLittle lämb\n";
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assert_eq!(lev_distance(a, b), 1);
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assert_eq!(lev_distance(b, a), 1);
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assert_eq!(lev_distance(a, c), 2);
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assert_eq!(lev_distance(c, a), 2);
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assert_eq!(lev_distance(b, c), 1);
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assert_eq!(lev_distance(c, b), 1);
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}
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#[test]
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fn test_find_best_match_for_name() {
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use crate::with_default_globals;
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with_default_globals(|| {
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let input = vec![Symbol::intern("aaab"), Symbol::intern("aaabc")];
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assert_eq!(
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find_best_match_for_name(input.iter(), "aaaa", None),
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Some(Symbol::intern("aaab"))
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);
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assert_eq!(
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find_best_match_for_name(input.iter(), "1111111111", None),
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None
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);
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let input = vec![Symbol::intern("aAAA")];
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assert_eq!(
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find_best_match_for_name(input.iter(), "AAAA", None),
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Some(Symbol::intern("aAAA"))
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);
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let input = vec![Symbol::intern("AAAA")];
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// Returns None because `lev_distance > max_dist / 3`
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assert_eq!(
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find_best_match_for_name(input.iter(), "aaaa", None),
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None
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);
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let input = vec![Symbol::intern("AAAA")];
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assert_eq!(
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find_best_match_for_name(input.iter(), "aaaa", Some(4)),
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Some(Symbol::intern("AAAA"))
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);
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})
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}
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