stemmer.js

// Porter stemmer in Javascript. Few comments, but it's easy to follow against the rules in the original
// paper, in
//
//  Porter, 1980, An algorithm for suffix stripping, Program, Vol. 14,
//  no. 3, pp 130-137,
//
// see also http://www.tartarus.org/~martin/PorterStemmer

// Release 1 be 'andargor', Jul 2004
// Release 2 (substantially revised) by Christopher McKenzie, Aug 2009

var stemmer = (function(){
	var step2list = {
			"ational" : "ate",
			"tional" : "tion",
			"enci" : "ence",
			"anci" : "ance",
			"izer" : "ize",
			"bli" : "ble",
			"alli" : "al",
			"entli" : "ent",
			"eli" : "e",
			"ousli" : "ous",
			"ization" : "ize",
			"ation" : "ate",
			"ator" : "ate",
			"alism" : "al",
			"iveness" : "ive",
			"fulness" : "ful",
			"ousness" : "ous",
			"aliti" : "al",
			"iviti" : "ive",
			"biliti" : "ble",
			"logi" : "log"
		},

		step3list = {
			"icate" : "ic",
			"ative" : "",
			"alize" : "al",
			"iciti" : "ic",
			"ical" : "ic",
			"ful" : "",
			"ness" : ""
		},

		c = "[^aeiou]",          // consonant
		v = "[aeiouy]",          // vowel
		C = c + "[^aeiouy]*",    // consonant sequence
		V = v + "[aeiou]*",      // vowel sequence

		mgr0 = "^(" + C + ")?" + V + C,               // [C]VC... is m>0
		meq1 = "^(" + C + ")?" + V + C + "(" + V + ")?$",  // [C]VC[V] is m=1
		mgr1 = "^(" + C + ")?" + V + C + V + C,       // [C]VCVC... is m>1
		s_v = "^(" + C + ")?" + v;                   // vowel in stem

	return function (w) {
		var 	stem,
			suffix,
			firstch,
			re,
			re2,
			re3,
			re4,
			origword = w;

		if (w.length < 3) { return w; }

		firstch = w.substr(0,1);
		if (firstch == "y") {
			w = firstch.toUpperCase() + w.substr(1);
		}

		// Step 1a
		re = /^(.+?)(ss|i)es$/;
		re2 = /^(.+?)([^s])s$/;

		if (re.test(w)) { w = w.replace(re,"$1$2"); }
		else if (re2.test(w)) {	w = w.replace(re2,"$1$2"); }

		// Step 1b
		re = /^(.+?)eed$/;
		re2 = /^(.+?)(ed|ing)$/;
		if (re.test(w)) {
			var fp = re.exec(w);
			re = new RegExp(mgr0);
			if (re.test(fp[1])) {
				re = /.$/;
				w = w.replace(re,"");
			}
		} else if (re2.test(w)) {
			var fp = re2.exec(w);
			stem = fp[1];
			re2 = new RegExp(s_v);
			if (re2.test(stem)) {
				w = stem;
				re2 = /(at|bl|iz)$/;
				re3 = new RegExp("([^aeiouylsz])\\1$");
				re4 = new RegExp("^" + C + v + "[^aeiouwxy]$");
				if (re2.test(w)) {	w = w + "e"; }
				else if (re3.test(w)) { re = /.$/; w = w.replace(re,""); }
				else if (re4.test(w)) { w = w + "e"; }
			}
		}

		// Step 1c
		re = /^(.+?)y$/;
		if (re.test(w)) {
			var fp = re.exec(w);
			stem = fp[1];
			re = new RegExp(s_v);
			if (re.test(stem)) { w = stem + "i"; }
		}

		// Step 2
		re = /^(.+?)(ational|tional|enci|anci|izer|bli|alli|entli|eli|ousli|ization|ation|ator|alism|iveness|fulness|ousness|aliti|iviti|biliti|logi)$/;
		if (re.test(w)) {
			var fp = re.exec(w);
			stem = fp[1];
			suffix = fp[2];
			re = new RegExp(mgr0);
			if (re.test(stem)) {
				w = stem + step2list[suffix];
			}
		}

		// Step 3
		re = /^(.+?)(icate|ative|alize|iciti|ical|ful|ness)$/;
		if (re.test(w)) {
			var fp = re.exec(w);
			stem = fp[1];
			suffix = fp[2];
			re = new RegExp(mgr0);
			if (re.test(stem)) {
				w = stem + step3list[suffix];
			}
		}

		// Step 4
		re = /^(.+?)(al|ance|ence|er|ic|able|ible|ant|ement|ment|ent|ou|ism|ate|iti|ous|ive|ize)$/;
		re2 = /^(.+?)(s|t)(ion)$/;
		if (re.test(w)) {
			var fp = re.exec(w);
			stem = fp[1];
			re = new RegExp(mgr1);
			if (re.test(stem)) {
				w = stem;
			}
		} else if (re2.test(w)) {
			var fp = re2.exec(w);
			stem = fp[1] + fp[2];
			re2 = new RegExp(mgr1);
			if (re2.test(stem)) {
				w = stem;
			}
		}

		// Step 5
		re = /^(.+?)e$/;
		if (re.test(w)) {
			var fp = re.exec(w);
			stem = fp[1];
			re = new RegExp(mgr1);
			re2 = new RegExp(meq1);
			re3 = new RegExp("^" + C + v + "[^aeiouwxy]$");
			if (re.test(stem) || (re2.test(stem) && !(re3.test(stem)))) {
				w = stem;
			}
		}

		re = /ll$/;
		re2 = new RegExp(mgr1);
		if (re.test(w) && re2.test(w)) {
			re = /.$/;
			w = w.replace(re,"");
		}

		// and turn initial Y back to y

		if (firstch == "y") {
			w = firstch.toLowerCase() + w.substr(1);
		}

		return w;
	}
})();
String.prototype.removeStopWords = function() {
	var x;
	var y;
	var word;
	var stop_word;
	var regex_str;
	var regex;
	var cleansed_string = this.valueOf();
	var stop_words = new Array(
		'a',
		'about',
		'above',
		'across',
		'after',
		'again',
		'against',
		'all',
		'almost',
		'alone',
		'along',
		'already',
		'also',
		'although',
		'always',
		'among',
		'an',
		'and',
		'another',
		'any',
		'anybody',
		'anyone',
		'anything',
		'anywhere',
		'are',
		'area',
		'areas',
		'around',
		'as',
		'ask',
		'asked',
		'asking',
		'asks',
		'at',
		'away',
		'b',
		'back',
		'backed',
		'backing',
		'backs',
		'be',
		'became',
		'because',
		'become',
		'becomes',
		'been',
		'before',
		'began',
		'behind',
		'being',
		'beings',
		'best',
		'better',
		'between',
		'big',
		'both',
		'but',
		'by',
		'c',
		'came',
		'can',
		'cannot',
		'case',
		'cases',
		'certain',
		'certainly',
		'clear',
		'clearly',
		'come',
		'could',
		'd',
		'did',
		'differ',
		'different',
		'differently',
		'do',
		'does',
		'done',
		'down',
		'down',
		'downed',
		'downing',
		'downs',
		'during',
		'e',
		'each',
		'early',
		'either',
		'end',
		'ended',
		'ending',
		'ends',
		'enough',
		'even',
		'evenly',
		'ever',
		'every',
		'everybody',
		'everyone',
		'everything',
		'everywhere',
		'f',
		'face',
		'faces',
		'fact',
		'facts',
		'far',
		'felt',
		'few',
		'find',
		'finds',
		'first',
		'for',
		'four',
		'from',
		'full',
		'fully',
		'further',
		'furthered',
		'furthering',
		'furthers',
		'g',
		'gave',
		'general',
		'generally',
		'get',
		'gets',
		'give',
		'given',
		'gives',
		'go',
		'going',
		'good',
		'goods',
		'got',
		'great',
		'greater',
		'greatest',
		'group',
		'grouped',
		'grouping',
		'groups',
		'h',
		'had',
		'has',
		'have',
		'having',
		'he',
		'her',
		'here',
		'herself',
		'high',
		'high',
		'high',
		'higher',
		'highest',
		'him',
		'himself',
		'his',
		'how',
		'however',
		'i',
		'if',
		'important',
		'in',
		'interest',
		'interested',
		'interesting',
		'interests',
		'into',
		'is',
		'it',
		'its',
		'itself',
		'j',
		'just',
		'k',
		'keep',
		'keeps',
		'kind',
		'knew',
		'know',
		'known',
		'knows',
		'l',
		'large',
		'largely',
		'last',
		'later',
		'latest',
		'least',
		'less',
		'let',
		'lets',
		'like',
		'likely',
		'long',
		'longer',
		'longest',
		'm',
		'made',
		'make',
		'making',
		'man',
		'many',
		'may',
		'me',
		'member',
		'members',
		'men',
		'might',
		'more',
		'most',
		'mostly',
		'mr',
		'mrs',
		'much',
		'must',
		'my',
		'myself',
		'n',
		'necessary',
		'need',
		'needed',
		'needing',
		'needs',
		'never',
		'new',
		'new',
		'newer',
		'newest',
		'next',
		'no',
		'nobody',
		'non',
		'noone',
		'not',
		'nothing',
		'now',
		'nowhere',
		'number',
		'numbers',
		'o',
		'of',
		'off',
		'often',
		'old',
		'older',
		'oldest',
		'on',
		'once',
		'one',
		'only',
		'open',
		'opened',
		'opening',
		'opens',
		'or',
		'order',
		'ordered',
		'ordering',
		'orders',
		'other',
		'others',
		'our',
		'out',
		'over',
		'p',
		'part',
		'parted',
		'parting',
		'parts',
		'per',
		'perhaps',
		'place',
		'places',
		'point',
		'pointed',
		'pointing',
		'points',
		'possible',
		'present',
		'presented',
		'presenting',
		'presents',
		'problem',
		'problems',
		'put',
		'puts',
		'q',
		'quite',
		'r',
		'rather',
		'really',
		'right',
		'right',
		'room',
		'rooms',
		's',
		'said',
		'same',
		'saw',
		'say',
		'says',
		'second',
		'seconds',
		'see',
		'seem',
		'seemed',
		'seeming',
		'seems',
		'sees',
		'several',
		'shall',
		'she',
		'should',
		'show',
		'showed',
		'showing',
		'shows',
		'side',
		'sides',
		'since',
		'small',
		'smaller',
		'smallest',
		'so',
		'some',
		'somebody',
		'someone',
		'something',
		'somewhere',
		'state',
		'states',
		'still',
		'still',
		'such',
		'sure',
		't',
		'take',
		'taken',
		'than',
		'that',
		'the',
		'their',
		'them',
		'then',
		'there',
		'therefore',
		'these',
		'they',
		'thing',
		'things',
		'think',
		'thinks',
		'this',
		'those',
		'though',
		'thought',
		'thoughts',
		'three',
		'through',
		'thus',
		'to',
		'today',
		'together',
		'too',
		'took',
		'toward',
		'turn',
		'turned',
		'turning',
		'turns',
		'two',
		'u',
		'under',
		'until',
		'up',
		'upon',
		'us',
		'use',
		'used',
		'uses',
		'v',
		'very',
		'w',
		'want',
		'wanted',
		'wanting',
		'wants',
		'was',
		'way',
		'ways',
		'we',
		'well',
		'wells',
		'went',
		'were',
		'what',
		'when',
		'where',
		'whether',
		'which',
		'while',
		'who',
		'whole',
		'whose',
		'why',
		'will',
		'with',
		'within',
		'without',
		'work',
		'worked',
		'working',
		'works',
		'would',
		'x',
		'y',
		'year',
		'years',
		'yet',
		'you',
		'young',
		'younger',
		'youngest',
		'your',
		'yours',
		'z'
	)

	// Split out all the individual words in the phrase
	words = cleansed_string.match(/[^\s]+|\s+[^\s+]$/g)

	// Review all the words
	if(!words)
		return null;
	for(x=0; x < words.length; x++) {
		// For each word, check all the stop words
		for(y=0; y < stop_words.length; y++) {
			// Get the current word
			word = words[x].replace(/\s+|[^a-z]+/ig, "");   // Trim the word and remove non-alpha

			// Get the stop word
			stop_word = stop_words[y];

			// If the word matches the stop word, remove it from the keywords
			if(word.toLowerCase() == stop_word) {
				// Build the regex
				regex_str = "^\\s*"+stop_word+"\\s*$";      // Only word
				regex_str += "|^\\s*"+stop_word+"\\s+";     // First word
				regex_str += "|\\s+"+stop_word+"\\s*$";     // Last word
				regex_str += "|\\s+"+stop_word+"\\s+";      // Word somewhere in the middle
				regex = new RegExp(regex_str, "ig");

				// Remove the word from the keywords
				cleansed_string = cleansed_string.replace(regex, " ");
			}
		}
	}
	return cleansed_string.replace(/^\s+|\s+$/g, "");
}