Sharkey/src/tools/analysis/naive-bayes.js

// Original source code: https://github.com/ttezel/bayes/blob/master/lib/naive_bayes.js (commit: 2c20d3066e4fc786400aaedcf3e42987e52abe3c)
// CUSTOMIZED BY SYUILO

/*
		Expose our naive-bayes generator function
*/
module.exports = function (options) {
	return new Naivebayes(options)
}

// keys we use to serialize a classifier's state
var STATE_KEYS = module.exports.STATE_KEYS = [
	'categories', 'docCount', 'totalDocuments', 'vocabulary', 'vocabularySize',
	'wordCount', 'wordFrequencyCount', 'options'
];

/**
 * Initializes a NaiveBayes instance from a JSON state representation.
 * Use this with classifier.toJson().
 *
 * @param  {String} jsonStr   state representation obtained by classifier.toJson()
 * @return {NaiveBayes}       Classifier
 */
module.exports.fromJson = function (jsonStr) {
	var parsed;
	try {
		parsed = JSON.parse(jsonStr)
	} catch (e) {
		throw new Error('Naivebayes.fromJson expects a valid JSON string.')
	}
	// init a new classifier
	var classifier = new Naivebayes(parsed.options)

	// override the classifier's state
	STATE_KEYS.forEach(function (k) {
		if (!parsed[k]) {
			throw new Error('Naivebayes.fromJson: JSON string is missing an expected property: `'+k+'`.')
		}
		classifier[k] = parsed[k]
	})

	return classifier
}

/**
 * Given an input string, tokenize it into an array of word tokens.
 * This is the default tokenization function used if user does not provide one in `options`.
 *
 * @param  {String} text
 * @return {Array}
 */
var defaultTokenizer = function (text) {
	//remove punctuation from text - remove anything that isn't a word char or a space
	var rgxPunctuation = /[^(a-zA-ZA-Яa-я0-9_)+\s]/g

	var sanitized = text.replace(rgxPunctuation, ' ')

	return sanitized.split(/\s+/)
}

/**
 * Naive-Bayes Classifier
 *
 * This is a naive-bayes classifier that uses Laplace Smoothing.
 *
 * Takes an (optional) options object containing:
 *   - `tokenizer`  => custom tokenization function
 *
 */
function Naivebayes (options) {
	// set options object
	this.options = {}
	if (typeof options !== 'undefined') {
		if (!options || typeof options !== 'object' || Array.isArray(options)) {
			throw TypeError('NaiveBayes got invalid `options`: `' + options + '`. Pass in an object.')
		}
		this.options = options
	}

	this.tokenizer = this.options.tokenizer || defaultTokenizer

	//initialize our vocabulary and its size
	this.vocabulary = {}
	this.vocabularySize = 0

	//number of documents we have learned from
	this.totalDocuments = 0

	//document frequency table for each of our categories
	//=> for each category, how often were documents mapped to it
	this.docCount = {}

	//for each category, how many words total were mapped to it
	this.wordCount = {}

	//word frequency table for each category
	//=> for each category, how frequent was a given word mapped to it
	this.wordFrequencyCount = {}

	//hashmap of our category names
	this.categories = {}
}

/**
 * Initialize each of our data structure entries for this new category
 *
 * @param  {String} categoryName
 */
Naivebayes.prototype.initializeCategory = function (categoryName) {
	if (!this.categories[categoryName]) {
		this.docCount[categoryName] = 0
		this.wordCount[categoryName] = 0
		this.wordFrequencyCount[categoryName] = {}
		this.categories[categoryName] = true
	}
	return this
}

/**
 * train our naive-bayes classifier by telling it what `category`
 * the `text` corresponds to.
 *
 * @param  {String} text
 * @param  {String} class
 */
Naivebayes.prototype.learn = function (text, category) {
	var self = this

	//initialize category data structures if we've never seen this category
	self.initializeCategory(category)

	//update our count of how many documents mapped to this category
	self.docCount[category]++

	//update the total number of documents we have learned from
	self.totalDocuments++

	//normalize the text into a word array
	var tokens = self.tokenizer(text)

	//get a frequency count for each token in the text
	var frequencyTable = self.frequencyTable(tokens)

	/*
			Update our vocabulary and our word frequency count for this category
	*/

	Object
	.keys(frequencyTable)
	.forEach(function (token) {
		//add this word to our vocabulary if not already existing
		if (!self.vocabulary[token]) {
			self.vocabulary[token] = true
			self.vocabularySize++
		}

		var frequencyInText = frequencyTable[token]

		//update the frequency information for this word in this category
		if (!self.wordFrequencyCount[category][token])
			self.wordFrequencyCount[category][token] = frequencyInText
		else
			self.wordFrequencyCount[category][token] += frequencyInText

		//update the count of all words we have seen mapped to this category
		self.wordCount[category] += frequencyInText
	})

	return self
}

/**
 * Determine what category `text` belongs to.
 *
 * @param  {String} text
 * @return {String} category
 */
Naivebayes.prototype.categorize = function (text) {
	var self = this
		, maxProbability = -Infinity
		, chosenCategory = null

	var tokens = self.tokenizer(text)
	var frequencyTable = self.frequencyTable(tokens)

	//iterate thru our categories to find the one with max probability for this text
	Object
	.keys(self.categories)
	.forEach(function (category) {

		//start by calculating the overall probability of this category
		//=>  out of all documents we've ever looked at, how many were
		//    mapped to this category
		var categoryProbability = self.docCount[category] / self.totalDocuments

		//take the log to avoid underflow
		var logProbability = Math.log(categoryProbability)

		//now determine P( w | c ) for each word `w` in the text
		Object
		.keys(frequencyTable)
		.forEach(function (token) {
			var frequencyInText = frequencyTable[token]
			var tokenProbability = self.tokenProbability(token, category)

			// console.log('token: %s category: `%s` tokenProbability: %d', token, category, tokenProbability)

			//determine the log of the P( w | c ) for this word
			logProbability += frequencyInText * Math.log(tokenProbability)
		})

		if (logProbability > maxProbability) {
			maxProbability = logProbability
			chosenCategory = category
		}
	})

	return chosenCategory
}

/**
 * Calculate probability that a `token` belongs to a `category`
 *
 * @param  {String} token
 * @param  {String} category
 * @return {Number} probability
 */
Naivebayes.prototype.tokenProbability = function (token, category) {
	//how many times this word has occurred in documents mapped to this category
	var wordFrequencyCount = this.wordFrequencyCount[category][token] || 0

	//what is the count of all words that have ever been mapped to this category
	var wordCount = this.wordCount[category]

	//use laplace Add-1 Smoothing equation
	return ( wordFrequencyCount + 1 ) / ( wordCount + this.vocabularySize )
}

/**
 * Build a frequency hashmap where
 * - the keys are the entries in `tokens`
 * - the values are the frequency of each entry in `tokens`
 *
 * @param  {Array} tokens  Normalized word array
 * @return {Object}
 */
Naivebayes.prototype.frequencyTable = function (tokens) {
	var frequencyTable = Object.create(null)

	tokens.forEach(function (token) {
		if (!frequencyTable[token])
			frequencyTable[token] = 1
		else
			frequencyTable[token]++
	})

	return frequencyTable
}

/**
 * Dump the classifier's state as a JSON string.
 * @return {String} Representation of the classifier.
 */
Naivebayes.prototype.toJson = function () {
	var state = {}
	var self = this
	STATE_KEYS.forEach(function (k) {
		state[k] = self[k]
	})

	var jsonStr = JSON.stringify(state)

	return jsonStr
}

// (original method)
Naivebayes.prototype.export = function () {
	var state = {}
	var self = this
	STATE_KEYS.forEach(function (k) {
		state[k] = self[k]
	})

	return state
}

module.exports.import = function (data) {
	var parsed = data

	// init a new classifier
	var classifier = new Naivebayes()

	// override the classifier's state
	STATE_KEYS.forEach(function (k) {
		if (!parsed[k]) {
			throw new Error('Naivebayes.import: data is missing an expected property: `'+k+'`.')
		}
		classifier[k] = parsed[k]
	})

	return classifier
}