pronounceable.js

// Luke Mitchell, 2016
// https://github.com/lukem512/pronounceable

var fs = require("fs");
var path = require("path");

var threshold = 0.001;

// Load probabilities from JSON files.
var tuples = JSON.parse(
    fs.readFileSync(path.resolve(__dirname, "data/tuples.json"), "utf8")
);
var triples = JSON.parse(
    fs.readFileSync(path.resolve(__dirname, "data/triples.json"), "utf8")
);

// Remove any non-alphabet characters
// and convert to lower case.
function clean(word) {
    return word.replace(/[^a-zA-Z0-9]/g, "").toLowerCase();
}

// Make a percentage.
function percent(score, count) {
    return score / count * 100;
}

// Check for undefined probabilities.
function undef(w, i, depth, probs) {
    if (depth <= 1) return typeof probs[w[i]] === "undefined";
    if (typeof probs[w[i]] === "undefined") return true;
    var nums = '0123456789';
    if (nums.indexOf(w[i]) !== -1) return true;
    return undef(w, i + 1, depth - 1, probs[w[i]]);
}

// Extract probabilities of word t 	uple.
function trainTuples(words) {
    var probs = {};
    var count = 0;

    words.forEach(function(w) {
	w = clean(w);

	for (var i = 0; i < w.length - 1; i++) {
	    if (!probs[w[i]]) probs[w[i]] = {};
	    if (!probs[w[i]][w[i + 1]]) probs[w[i]][w[i + 1]] = 1;
	    else probs[w[i]][w[i + 1]]++;
	    count++;
	}
    });

    Object.keys(probs).forEach(function(first) {
	Object.keys(probs[first]).forEach(function(second) {
	    probs[first][second] = percent(probs[first][second], count);
	});
    });

    return probs;
}

// Extract probabilities of word triples.
function trainTriples(words) {
    var probs = {};
    var count = 0;

    words.forEach(function(w) {
	w = clean(w);

	for (var i = 0; i < w.length - 2; i++) {
	    if (!probs[w[i]]) probs[w[i]] = {};
	    if (!probs[w[i]][w[i + 1]]) probs[w[i]][w[i + 1]] = {};
	    if (!probs[w[i]][w[i + 1]][w[i + 2]]) probs[w[i]][w[i + 1]][w[i + 2]] = 1;
	    else probs[w[i]][w[i + 1]][w[i + 2]]++;
	    count++;
	}
    });

    Object.keys(probs).forEach(function(first) {
	Object.keys(probs[first]).forEach(function(second) {
	    Object.keys(probs[first][second]).forEach(function(third) {
		probs[first][second][third] = percent(
		    probs[first][second][third],
		    count
		);
	    });
	});
    });

    return probs;
}

// Extract probabilities of word tuples and triples
// from a large list of words.
module.exports.train = function(filename, callback) {
    fs.readFile(filename, "utf8", function read(err, data) {
	if (err) throw err;

	var words = data.trim().split(/\s+/);
	var tuples = trainTuples(words);
	var triples = trainTriples(words);

	callback(tuples, triples);
    });
};

// Check whether a word is pronounceable using
// the word tuple probabilities.
module.exports.test = function(word) {
    var w = clean(word);

    switch (w.length) {
    case 1:
	break;

    case 2:
	for (var i = 0; i < w.length - 1; i++) {
            if (undef(w, i, 2, tuples)) return false;
            if (tuples[w[i]][w[i + 1]] < threshold) return false;
	}

    default:
	for (var i = 0; i < w.length - 2; i++) {
            if (undef(w, i, 3, triples)) return false;
            if (triples[w[i]][w[i + 1]][w[i + 2]] < threshold) return false;
	}
    }
    var vowels = 'aeiouy';
    var countVowel = 0;
    for (var i = 0; i < w.length; i++) {
	if (vowels.indexOf(w[i]) !== -1) {
	    countVowel++; // found a vowel, add it to the count
	}
    }
    if (countVowel == 0) return false;

    return true;
};

// Compute a normalised score for
// the pronounceability of the word.
module.exports.score = function(word) {
    var w = clean(word);
    var score = 0;

    switch (w.length) {
    case 1:
	return 1;

    case 2:
	for (var i = 0; i < w.length - 1; i++) {
            if (undef(w, i, 2, tuples)) {
		score = score + 0;
            } else {
		score = score + tuples[w[i]][w[i + 1]];
            }
	}

    default:
	for (var i = 0; i < w.length - 2; i++) {
            if (undef(w, i, 3, triples)) {
		score = score + 0;
            } else {
		score = score + triples[w[i]][w[i + 1]][w[i + 2]];
            }
	}
    }

    var vowels = 'aeiouy';
    var countVowel = 0;
    for (var i = 0; i < w.length; i++) {
	if (vowels.indexOf(w[i]) !== -1) {
	    countVowel++; // found a vowel, add it to the count
	}
    }
    if (countVowel == 0) return 0;


    return score / w.length;
};