pos/POSTagger.js

fasttag part of speech tagger implementation

/*!
 * jsPOS
 *
 * Copyright 2010, Percy Wegmann
 * Licensed under the LGPLv3 license
 * http://www.opensource.org/licenses/lgpl-3.0.html
 */

var TransformationRules = require('./BrillTransformationRules');
var transformationRules = new TransformationRules();

module.exports = POSTagger;
function POSTagger(){
    this.lexicon = require('./lexicon');
}

POSTagger.prototype.wordInLexicon = function(word){
    var ss = this.lexicon[word];
    if (ss != null)
        return true;
    // 1/22/2002 mod (from Lisp code): if not in hash, try lower case:
    if (!ss)
        ss = this.lexicon[word.toLowerCase()];
    if (ss)
        return true;
    return false;
}

POSTagger.prototype.tag = function(words) {
  var taggedSentence = new Array(words.length);

  // Initialise taggedSentence with words and initial categories
  for (var i = 0, size = words.length; i < size; i++) {
    taggedSentence[i] = new Array(2);
    taggedSentence[i][0] = words[i];
    // lexicon maps a word to an array of possible categories
    var ss = this.lexicon[words[i]];
    // 1/22/2002 mod (from Lisp code): if not in hash, try lower case:
    if (!ss)
      ss = this.lexicon[words[i].toLowerCase()];
    if (!ss && (words[i].length === 1))
      taggedSentence[i][1] = words[i] + "^";
    // We need to catch scenarios where we pass things on the prototype
    // that aren't in the lexicon: "constructor" breaks this otherwise
    if (!ss || (Object.prototype.toString.call(ss) !== '[object Array]'))
      taggedSentence[i][1] = "NN";
    else
      taggedSentence[i][1] = ss[0];
  }

  // Apply transformation rules
  taggedSentence.forEach(function(taggedWord, index) {
    transformationRules.getRules().forEach(function(rule) {
      rule(taggedSentence, index);
    });
  });
  return taggedSentence;
}

POSTagger.prototype.prettyPrint = function(taggedWords) {
	for (i in taggedWords) {
        print(taggedWords[i][0] + "(" + taggedWords[i][1] + ")");
    }
}

POSTagger.prototype.extendLexicon = function(lexicon) {
  for (var word in lexicon) {
    if (!this.lexicon.hasOwnProperty(word)) {
      this.lexicon[word] = lexicon[word];
    }
  }
}

// console.log(new POSTagger().tag(["i", "went", "to", "the", "store", "to", "buy", "5.2", "gallons", "of", "milk"]));