JSymSpell

JSymSpell is a zero-dependency Java 8+ port of SymSpell

Overview

The Symmetric Delete spelling correction algorithm speeds up the process up by orders of magnitude.

It achieves this by generating delete-only candidates in advance from a given lexicon.

Setup

Add the latest JSymSpell dependency to your project

Getting Started

To start, we'll load the data sets of unigrams and bigrams:

Map<Bigram, Long> bigrams = Files.lines(Paths.get("src/test/resources/bigrams.txt"))
                                 .map(line -> line.split(" "))
                                 .collect(Collectors.toMap(tokens -> new Bigram(tokens[0], tokens[1]), tokens -> Long.parseLong(tokens[2])));
Map<String, Long> unigrams = Files.lines(Paths.get("src/test/resources/words.txt"))
                                  .map(line -> line.split(","))
                                  .collect(Collectors.toMap(tokens -> tokens[0], tokens -> Long.parseLong(tokens[1])));

Let's now create an instance of SymSpell by using the builder and load these maps. For this example we'll limit the max edit distance to 2:

SymSpell symSpell = new SymSpellBuilder().setUnigramLexicon(unigrams)
                                         .setBigramLexicon(bigrams)
                                         .setMaxDictionaryEditDistance(2)
                                         .createSymSpell();

And we are ready!

int maxEditDistance = 2;
boolean includeUnknowns = false;
List<SuggestItem> suggestions = symSpell.lookupCompound("Nostalgiais truly one of th greatests human weakneses", maxEditDistance, includeUnknowns);
System.out.println(suggestions.get(0).getSuggestion());
// Output: nostalgia is truly one of the greatest human weaknesses
// ... only second to the neck!

Custom String Distance Algorithms

By default, JSymSpell calculates Damerau-Levenshtein distance. Depending on your use case, you may want to use a different one.

Other algorithms to calculate String Distance that might result of interest are:

• Hamming Distance
• Jaro Distance
• Keyboard distance

Here's an example using Hamming Distance:

SymSpell symSpell = new SymSpellBuilder().setUnigramLexicon(unigrams)
                                         .setStringDistanceAlgorithm((string1, string2, maxDistance) -> {
                                             if (string1.length() != string2.length()){
                                                 return -1;
                                             }
                                             char[] chars1 = string1.toCharArray();
                                             char[] chars2 = string2.toCharArray();
                                             int distance = 0;
                                             for (int i = 0; i < chars1.length; i++) {
                                                 if (chars1[i] != chars2[i]) {
                                                     distance += 1;
                                                 }
                                             }
                                             return distance;
                                         })
                                         .createSymSpell();

Custom character comparison

Let's say you are building a query engine for country names where the input form allows Unicode characters, but the database is all ASCII. You might want searches for Espana to return España entries with distance 0:

CharComparator customCharComparator = new CharComparator() {
    @Override
    public boolean areEqual(char ch1, char ch2) {
        if (ch1 == 'ñ' || ch2 == 'ñ') {
            return ch1 == 'n' || ch2 == 'n';
        }
        return ch1 == ch2;
    }
};
StringDistance damerauLevenshteinOSA = new DamerauLevenshteinOSA(customCharComparator);
SymSpell symSpell = new SymSpellBuilder().setUnigramLexicon(Map.of("España", 10L))
                                         .setStringDistanceAlgorithm(damerauLevenshteinOSA)
                                         .createSymSpell();
List<SuggestItem> suggestions = symSpell.lookup("Espana", Verbosity.ALL);
assertEquals(0, suggestions.get(0).getEditDistance());

Frequency dictionaries in other languages

As in the original SymSpell project, this port contains an English frequency dictionary that you can find at src/test/resources/words.txt If you need a different one, you just need to compute a Map<String, Long> where the key is the word and the value is the frequency in the corpus.

Map<String, Long> unigrams = Arrays.stream("A B A B C A B A C A".split(" "))
                                   .collect(Collectors.groupingBy(String::toLowerCase, Collectors.counting()));
System.out.println(unigrams);
// Output: {a=5, b=3, c=2}

Built With

• Maven - Dependency Management

Versioning

We use SemVer for versioning.

License

This project is licensed under the MIT License - see the LICENSE.md file for details

Acknowledgments

• Wolf Garbe