85 lines
3 KiB
Rust
85 lines
3 KiB
Rust
// Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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use ast::Name;
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use std::cmp;
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use parse::token::InternedString;
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/// To find 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() + 1).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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} dcol[t_last + 1]
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}
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/// To find the best match for a given string from an iterator of names
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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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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<InternedString>
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where T: Iterator<Item = &'a Name> {
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let max_dist = dist.map_or_else(|| cmp::max(lookup.len(), 3) / 3, |d| d);
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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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match dist <= max_dist { // filter the unwanted cases
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true => Some((name.as_str(), dist)),
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false => None,
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}
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})
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.min_by_key(|&(_, val)| val) // extract the tuple containing the minimum edit distance
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.map(|(s, _)| s) // and return only the string
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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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