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//! Levenshtein distances.
//!
//! The [Levenshtein distance] is a metric for measuring the difference between two strings.
//!
//! [Levenshtein distance]: https://en.wikipedia.org/wiki/Levenshtein_distance
use crate::symbol::Symbol;
use std::cmp;
#[cfg(test)]
mod tests;
/// Finds the Levenshtein distance between two strings.
pub fn lev_distance(a: &str, b: &str) -> usize {
// cases which don't require further computation
if a.is_empty() {
return b.chars().count();
} else if b.is_empty() {
return a.chars().count();
}
let mut dcol: Vec<_> = (0..=b.len()).collect();
let mut t_last = 0;
for (i, sc) in a.chars().enumerate() {
let mut current = i;
dcol[0] = current + 1;
for (j, tc) in b.chars().enumerate() {
let next = dcol[j + 1];
if sc == tc {
dcol[j + 1] = current;
} else {
dcol[j + 1] = cmp::min(current, next);
dcol[j + 1] = cmp::min(dcol[j + 1], dcol[j]) + 1;
}
current = next;
t_last = j;
}
}
dcol[t_last + 1]
}
/// Finds the best match for a given word in the given iterator.
///
/// As a loose rule to avoid the obviously incorrect suggestions, it takes
/// an optional limit for the maximum allowable edit distance, which defaults
/// to one-third of the given word.
///
/// Besides Levenshtein, we use case insensitive comparison to improve accuracy
/// on an edge case with a lower(upper)case letters mismatch.
#[cold]
pub fn find_best_match_for_name(
name_vec: &[Symbol],
lookup: Symbol,
dist: Option<usize>,
) -> Option<Symbol> {
let lookup = &lookup.as_str();
let max_dist = dist.unwrap_or_else(|| cmp::max(lookup.len(), 3) / 3);
// Priority of matches:
// 1. Exact case insensitive match
// 2. Levenshtein distance match
// 3. Sorted word match
if let Some(case_insensitive_match) =
name_vec.iter().find(|candidate| candidate.as_str().to_uppercase() == lookup.to_uppercase())
{
return Some(*case_insensitive_match);
}
let levenshtein_match = name_vec
.iter()
.filter_map(|&name| {
let dist = lev_distance(lookup, &name.as_str());
if dist <= max_dist { Some((name, dist)) } else { None }
})
// Here we are collecting the next structure:
// (levenshtein_match, levenshtein_distance)
.fold(None, |result, (candidate, dist)| match result {
None => Some((candidate, dist)),
Some((c, d)) => Some(if dist < d { (candidate, dist) } else { (c, d) }),
});
if levenshtein_match.is_some() {
levenshtein_match.map(|(candidate, _)| candidate)
} else {
find_match_by_sorted_words(name_vec, lookup)
}
}
fn find_match_by_sorted_words(iter_names: &[Symbol], lookup: &str) -> Option<Symbol> {
iter_names.iter().fold(None, |result, candidate| {
if sort_by_words(&candidate.as_str()) == sort_by_words(lookup) {
Some(*candidate)
} else {
result
}
})
}
fn sort_by_words(name: &str) -> String {
let mut split_words: Vec<&str> = name.split('_').collect();
// We are sorting primitive &strs and can use unstable sort here.
split_words.sort_unstable();
split_words.join("_")
}
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