lemmatizer/dist/index.js

English language lemmatizer

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
const prefixes_1 = require("./prefixes");
const en_lexicon_1 = require("en-lexicon");
const en_stemmer_1 = require("en-stemmer");
const en_inflectors_1 = require("en-inflectors");
function lemmatizer(string) {
    return safeStemmer(verbsAndNouns(unprefixer(string)));
}
exports.lemmatizer = lemmatizer;
function unprefixer(string) {
    prefixes_1.prefixes.forEach((prefix) => {
        if (string.startsWith(prefix) && en_lexicon_1.lexicon[string.substr(prefix.length)]) {
            string = string.substr(prefix.length);
        }
    });
    return string;
}
exports.unprefixer = unprefixer;
function verbsAndNouns(token) {
    if (isVerb(token))
        return new en_inflectors_1.Inflectors(token).toPresent();
    else if (isPluralNoun(token))
        return new en_inflectors_1.Inflectors(token).toSingular();
    return token;
}
function safeStemmer(string) {
    const stem = en_stemmer_1.stemmer(string);
    if (en_lexicon_1.lexicon[stem])
        return stem;
    else if (en_lexicon_1.lexicon[stem + "e"])
        return stem + "e";
    else if (en_lexicon_1.lexicon[stem + "y"])
        return stem + "y";
    else if (en_lexicon_1.lexicon[stem + "l"])
        return stem + "l";
    else
        return string;
}
function isVerb(string) {
    if (en_lexicon_1.lexicon[string] && en_lexicon_1.lexicon[string].split("|").find(x => x.startsWith("V")))
        return true;
    else
        return false;
}
function isPluralNoun(string) {
    if (en_lexicon_1.lexicon[string] && en_lexicon_1.lexicon[string].split("|").find(x => x.startsWith("N") && x.endsWith("S")))
        return true;
    else
        return false;
}
exports.default = lemmatizer;