porterstemmer.ts

// 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

export 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;
    }
})();