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//! stringedits contains the [Edit] trait, which provides access to a number of iterators for small edits to strings. //! Based off the article [How to Write A Spelling Corrector](https://norvig.com/spell-correct.html) by Peter Norvig. //! Available under the MIT license. //! //! Usage: //! ``` //! # use stringedits::Edit; //! assert_eq!(vec!["!foo", "f!oo", "fo!o", "foo!"], "foo".inserts(&['!']).collect::<Vec<String>>()); //! ``` //! #[cfg(test)] mod tests; use std::collections::HashSet; /// The characters from 'a'..='z'. pub const ASCII_LOWERCASE: &[char] = &[ 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', ]; /// The characters from 'A'..='Z'. pub const ASCII_UPPERCASE: &[char] = &[ 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', ]; /// The Edit trait provides access to a number of iterators for single-and-double character edits of a string. /// It is implemented for any type that implements `AsRef<str>`. pub trait Edit: AsRef<str> { /// create an iterator over all the splits at a single position of a word. /// ``` /// # use stringedits::Edit; /// # use std::collections::HashSet; /// let want: HashSet<(String, String)> = vec![("", "foo"), ("f", "oo"), ("fo", "o"), ("foo", "")] /// .into_iter() /// .map(|(a, b)| (a.to_string(), b.to_string())) /// .collect(); /// let got: HashSet<(String, String)> = "foo".splits().map(|(q, r)| (q.to_string(), r.to_string())).collect(); /// assert_eq!(want, got); /// ``` fn splits(&self) -> Splits { Splits { word: self.as_ref(), i: 0, } } /// create an iterator over all distance-1 transpositions of a word /// ``` /// # use stringedits::Edit; /// # use std::collections::HashSet; /// let transpositions = "bar".transposes().collect::<Vec<String>>().join(" "); /// assert_eq!(transpositions, "abr bra"); /// ``` fn transposes(&self) -> Transposes { Transposes(self.splits()) } /// an iterator over all distance-1 replacements with a lowercase ASCII letter (`'a'..='z'`) /// ``` /// # use stringedits::Edit; /// let replaces = "ab".replaces_ascii_lowercase().collect::<Vec<String>>().join(" "); /// let want = concat!( /// "ab bb cb db eb fb gb hb ib jb kb lb mb nb ob pb qb rb sb tb ub vb wb xb yb zb ", // replace 'a' /// "aa ab ac ad ae af ag ah ai aj ak al am an ao ap aq ar as at au av aw ax ay az", // replace 'b' /// ); /// assert_eq!(want, replaces) /// ``` fn replaces_ascii_lowercase(&self) -> CustomReplaces { CustomReplaces { splits: self.splits(), current: None, i: 0, alphabet: ASCII_LOWERCASE, } } /// create an iterator over all distance-1 insertions of a lowercase ASCII letter (`'b'a..=b'z'`) /// ``` /// # use stringedits::{Edit, ASCII_LOWERCASE}; /// let a_inserts = "a".inserts(ASCII_LOWERCASE).collect::<Vec<String>>().join(" "); /// let want = concat!( /// "aa ba ca da ea fa ga ha ia ja ka la ma na oa pa qa ra sa ta ua va wa xa ya za ", // insert before a /// "aa ab ac ad ae af ag ah ai aj ak al am an ao ap aq ar as at au av aw ax ay az" // insert after a /// ); /// assert_eq!(want, a_inserts); /// ``` fn inserts_ascii_lowercase(&self) -> CustomInsert { CustomInsert { splits: self.splits(), i: 0, current: None, alphabet: ASCII_LOWERCASE, } } /// create an iterator over all single-character deletions of a word /// ``` /// # use stringedits::Edit; /// let deletions = "bar".deletions().collect::<Vec<String>>().join(" "); /// assert_eq!("ar br ba", deletions); /// ``` fn deletions(&self) -> Deletions { Deletions(self.splits()) } /// create an iterator over all distance-1 edits of the string; that is, the transposes, replacements, insertions, and deletions /// ``` /// # use stringedits::{Edit, ASCII_LOWERCASE}; /// # use std::collections::HashSet; /// let got: HashSet<String> = "bar".dist1edits(ASCII_LOWERCASE).collect(); /// assert!(got.contains("br")); // deletion /// assert!(got.contains("bbar")); // addition /// assert!(got.contains("bra")); // transposition /// assert!(got.contains("baz")); // substitution /// ``` fn dist1edits<'a>(&'a self, alphabet: &'a [char]) -> Dist1Edits { Dist1Edits { deletes: self.deletions(), transposes: self.transposes(), replaces: self.replaces(alphabet), inserts: self.inserts(alphabet), } } /// an iterator over all distance-2 edits of the string; that is, the combinations of up two transpositions, replacements, insertions, and/or deletions /// ``` /// # use stringedits::{Edit, ASCII_LOWERCASE}; /// # use std::collections::HashSet; /// let dist2: HashSet<String> = "foo".dist2edits(ASCII_LOWERCASE).collect(); /// assert!(dist2.contains("f")); // two deletions /// assert!(dist2.contains("afooa")); // two additions /// assert!(dist2.contains("of")); // delete & transpose /// assert!(dist2.contains("ofog")); // transposition and addition /// ``` fn dist2edits<'a>(&'a self, alphabet: &'a [char]) -> Dist2Edits { let mut d1 = self .dist1edits(alphabet) .collect::<HashSet<String>>() .into_iter(); let current_d2 = d1 .next() .unwrap() .dist1edits(alphabet) .collect::<Vec<String>>() .into_iter(); Dist2Edits { d1, current_d2, alphabet, } } /// An iterator over all distance_1 replacements into the string using the provided alphabet. ("bar" -> "baa", "baz") /// ``` /// # use stringedits::{Edit, ASCII_LOWERCASE}; /// assert_eq!("foo".replaces(ASCII_LOWERCASE).collect::<String>(), "foo".replaces(ASCII_LOWERCASE).collect::<String>()); /// assert_eq!("!oo f!o fo!", "foo".replaces(&['!']).collect::<Vec<String>>().join(" ")); /// ``` fn replaces<'a>(&'a self, alphabet: &'a [char]) -> CustomReplaces<'a> { CustomReplaces { splits: self.splits(), i: 0, current: None, alphabet, } } /// An iterator over all distance-1 insertions into the string using the provided alphabet. ("bar" -> "bard", "boar") /// These insertions include before the first character and after the last one; however, an empty string will only be inserted into once. /// See [ASCII_LOWERCASE] and [ASCII_UPPERCASE] for useful alphabets. /// ``` /// # use stringedits::{Edit, ASCII_LOWERCASE}; /// assert_eq!(vec!["!foo", "f!oo", "fo!o", "foo!"], "foo".inserts(&['!']).collect::<Vec<String>>()); /// assert_eq!("1234", "".inserts(&['1', '2', '3', '4']).collect::<String>()); /// ``` fn inserts<'a>(&'a self, alphabet: &'a [char]) -> CustomInsert<'a> { CustomInsert { splits: self.splits(), i: 0, current: None, alphabet, } } } impl<T: AsRef<str>> Edit for T {} /// Iterator over all the distance-2 edits of a word. See [Edit::dist2edits] /// This stores a fairly large hashset & vector (of distance-1 edits) internally, /// so it's not nearly as lightweight as the other iterator adaptors. /// I'd like to come up with a more elegant solution if I can, but I'd have to wrestle with lifetimes a lot. /// pub struct Dist2Edits<'a> { d1: <std::collections::HashSet<String> as IntoIterator>::IntoIter, current_d2: <Vec<String> as IntoIterator>::IntoIter, alphabet: &'a [char], } ///Iterator over all the splits at a single position of a word. See [Edit::splits] #[derive(Debug, Clone)] pub struct Splits<'a> { word: &'a str, i: usize, } /// Iterator over all transpositions of a single position of a word. See [Edit::transposes] #[derive(Debug, Clone)] pub struct Transposes<'a>(Splits<'a>); ///Iterator over all the words formed from the delition of a single character from a word. /// See [Edit::deletions] #[derive(Debug, Clone)] pub struct Deletions<'a>(Splits<'a>); ///Iterator over all the words formed from the replacement of a character in a word with a letter in a...z /// see [Edit::replaces] #[derive(Debug, Clone)] pub struct Replaces<'a> { splits: Splits<'a>, current: Option<(String, String)>, c: u8, } ///Iterator over all the words formed from the replacement of a character in a word with each letter in it's custom alphabet /// see [Edit::replaces] #[derive(Debug, Clone)] pub struct CustomReplaces<'a> { splits: Splits<'a>, current: Option<(&'a str, &'a str)>, alphabet: &'a [char], i: usize, } #[derive(Debug, Clone)] pub struct CustomInsert<'a> { splits: Splits<'a>, current: Option<(&'a str, &'a str)>, alphabet: &'a [char], i: usize, } /// Iterator over all the words formed from the insertion of a letter in a...z in any position in a word, including before the first character and after the last /// see [Edit::inserts] #[derive(Debug, Clone)] pub struct Inserts<'a> { splits: Splits<'a>, current: Option<(String, String)>, c: u8, } ///Iterator over all the distance-1 edits of a word; deletion, insertion, or replacement of one character, ///or transposition of two characters. See [Edit::dist1edits] #[derive(Debug, Clone)] pub struct Dist1Edits<'a> { deletes: Deletions<'a>, transposes: Transposes<'a>, replaces: CustomReplaces<'a>, inserts: CustomInsert<'a>, } // -------- ITERATORS ------ impl<'a> Iterator for Dist2Edits<'a> { type Item = String; fn next(&mut self) -> Option<String> { if let Some(d2) = self.current_d2.next() { return Some(d2); } if let Some(s) = self.d1.next() { self.current_d2 = s .dist1edits(self.alphabet) .collect::<Vec<String>>() .into_iter(); self.next() } else { None } } } impl<'a> Iterator for CustomReplaces<'a> { type Item = String; fn next(&mut self) -> Option<Self::Item> { match self { CustomReplaces { current: Some((a, b)), i, alphabet, .. } if *i < alphabet.len() && !a.is_empty() => { let mut replace = a.to_string(); replace.pop(); replace.push(alphabet[*i] as char); *i += 1; Some(replace + b) } _ => match self.splits.next() { None => None, Some((a, b)) => { self.i = 0; self.current = Some((a, b)); self.next() } }, } } } impl<'a> Iterator for CustomInsert<'a> { type Item = String; fn next(&mut self) -> Option<Self::Item> { match self { CustomInsert { current: Some((a, b)), i, alphabet, .. } if *i < alphabet.len() => { let mut replace = a.to_string(); replace.push(alphabet[*i] as char); *i += 1; Some(replace + b) } _ => match self.splits.next() { None => None, Some((a, b)) => { self.i = 0; self.current = Some((a, b)); self.next() } }, } } } impl<'a> Iterator for Deletions<'a> { type Item = String; fn next(&mut self) -> Option<Self::Item> { match self.0.next() { None => None, Some((_, ref b)) if b.is_empty() => self.next(), Some((a, b)) => Some(a.to_owned() + &b[1..]), } } } impl<'a> Iterator for Transposes<'a> { type Item = String; fn next(&mut self) -> Option<Self::Item> { match self.0.next() { None => None, Some((_, ref b)) if b.len() < 2 => self.next(), //we can only transpose the rightmost two characters if there are two or more Some((a, b)) => { let mut transpose = a.to_string(); let chars: Vec<char> = b.chars().collect(); transpose.push(chars[1]); transpose.push(chars[0]); transpose.extend(&chars[2..]); Some(transpose) } } } } impl<'a> Iterator for Splits<'a> { type Item = (&'a str, &'a str); fn next(&mut self) -> Option<Self::Item> { if self.i > self.word.len() { return None; } let n = self.i; self.i += 1; Some((&self.word[..n], &self.word[n..])) } } impl<'a> Iterator for Dist1Edits<'a> { type Item = String; fn next(&mut self) -> Option<String> { self.deletes .next() .or_else(|| self.transposes.next()) .or_else(|| self.inserts.next()) .or_else(|| self.replaces.next()) } }