Struct fst::Levenshtein
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pub struct Levenshtein { // some fields omitted }
A Unicode aware Levenshtein automaton for running efficient fuzzy queries.
A Levenshtein automata is one way to search any finite state transducer for keys that approximately match a given query. A Levenshtein automaton approximates this by returning all keys within a certain edit distance of the query. The edit distance is defined by the number of insertions, deletions and substitutions required to turn the query into the key. Insertions, deletions and substitutions are based on Unicode characters (where each character is a single Unicode scalar value).
Example
This example shows how to find all keys within an edit distance of 1
from foo
.
use fst::{IntoStreamer, Streamer, Levenshtein, Set}; let keys = vec!["fa", "fo", "fob", "focus", "foo", "food", "foul"]; let set = Set::from_iter(keys).unwrap(); let lev = Levenshtein::new("foo", 1).unwrap(); let mut stream = set.search(&lev).into_stream(); let mut keys = vec![]; while let Some(key) = stream.next() { keys.push(key.to_vec()); } assert_eq!(keys, vec![ "fo".as_bytes(), // 1 deletion "fob".as_bytes(), // 1 substitution "foo".as_bytes(), // 0 insertions/deletions/substitutions "food".as_bytes(), // 1 insertion ]);
This example only uses ASCII characters, but it will work equally well on Unicode characters.
Warning: experimental
While executing this Levenshtein automaton against a finite state transducer will be very fast, constructing an automaton may not be. Namely, this implementation is a proof of concept. While I believe the algorithmic complexity is not exponential, the implementation is not speedy and it can use enormous amounts of memory (tens of MB before a hard-coded limit will cause an error to be returned).
This is important functionality, so one should count on this implementation being vastly improved in the future.
Methods
impl Levenshtein
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fn new(query: &str, distance: u32) -> Result<Self>
Create a new Levenshtein query.
The query finds all matching terms that are at most distance
edit operations from query
. (An edit operation may be an insertion,
a deletion or a substitution.)
If the underlying automaton becomes too big, then an error is returned.
A Levenshtein
value satisfies the Automaton
trait, which means it
can be used with the search
method of any finite state transducer.
Trait Implementations
impl Debug for Levenshtein
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impl Automaton for Levenshtein
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type State = Option<usize>
The type of the state used in the automaton.
fn start(&self) -> Option<usize>
Returns a single start state for this automaton. Read more
fn is_match(&self, state: &Option<usize>) -> bool
Returns true if and only if state
is a match state.
fn can_match(&self, state: &Option<usize>) -> bool
Returns true if and only if state
can lead to a match in zero or more steps. Read more
fn accept(&self, state: &Option<usize>, byte: u8) -> Option<usize>
Return the next state given state
and an input.
fn will_always_match(&self, _state: &Self::State) -> bool
Returns true if and only if state
matches and must match no matter what steps are taken. Read more
fn starts_with(self) -> StartsWith<Self> where Self: Sized
Returns an automaton that matches the strings that start with something this automaton matches. Read more
fn union<Rhs: Automaton>(self, rhs: Rhs) -> Union<Self, Rhs> where Self: Sized
Returns an automaton that matches the strings matched by either this or the other automaton. Read more
fn intersection<Rhs: Automaton>(self, rhs: Rhs) -> Intersection<Self, Rhs> where Self: Sized
Returns an automaton that matches the strings matched by both this and the other automaton. Read more
fn complement(self) -> Complement<Self> where Self: Sized
Returns an automaton that matches the strings not matched by this automaton.