zpwiki/pages/students/2016/jan_holp/dp2021/dp2021 zdrojove subory/pagerank.js

//"use strict";
// pagerank.js 0.0.1

//Use a random surfer algorithm to determine the relative 
//rank of nodes. The importance of each node is determined
//by the number of incoming links as well as the importance 
//of those incoming links. 

// Expose
// ----------

//Expose our library to be called externally
module.exports = function (nodeMatrix, linkProb, tolerance, callback, debug) {
    if (!nodeMatrix || !linkProb || !tolerance || !callback) {
        throw new Error("Provide 4 arguments: "+
            "nodeMatrix, link probability, tolerance, callback");
    }
    //If debug is unset set it to false
    if (!debug) { 
        debug=false;
    }
    return new Pagerank(nodeMatrix, linkProb, tolerance, callback, debug);
};

// Initialize
// ----------
function Pagerank(nodeMatrix, linkProb, tolerance, callback, debug) {
    //**OutgoingNodes:** represents an array of nodes. Each node in this 
    //array contains an array of nodes to which the corresponding node has
    //outgoing links.
    this.outgoingNodes = nodeMatrix;

    //console.log(this.outgoingNodes);
    //**LinkProb:** a value ??
    this.linkProb = linkProb;
    //**Tolerance:** the point at which a solution is deemed optimal. 
    //Higher values are more accurate, lower values are faster to computer. 
    this.tolerance = tolerance;
    this.callback = callback;

    //Number of outgoing nodes
    this.pageCount = Object.keys(this.outgoingNodes).length;
    //console.log(this.pageCount);
    //**Coeff:** coefficient for the likelihood that a page will be visited.
    this.coeff = (1-linkProb)/this.pageCount;
    
    this.probabilityNodes = !(nodeMatrix instanceof Array) ? {} : [];
    this.incomingNodes = !(nodeMatrix instanceof Array) ? {} : [];
    //console.log(this.incomingNodes);
    this.debug=debug;
    
    this.startRanking();
}

//Start ranking 
// ----------
Pagerank.prototype.startRanking = function () {

    //we initialize all of our probabilities
    var initialProbability = 1/this.pageCount, 
        outgoingNodes = this.outgoingNodes, i, a, index;
    
    //rearray the graph and generate initial probability
    for (i in outgoingNodes) {
        this.probabilityNodes[i]=initialProbability;
        for (a in outgoingNodes[i]) {
            index = outgoingNodes[i][a];
            if (!this.incomingNodes[index]) {
                this.incomingNodes[index]=[]; 
            }
            this.incomingNodes[index].push(i);
               // console.log(this.incomingNodes);

        }
    }

    //if debug is set, print each iteration
    if (this.debug) this.reportDebug(1)
    
    this.iterate(1);
};

//Log iteration to console 
// ----------
Pagerank.prototype.reportDebug = function (count) {
    //console.log("____ITERATION "+count+"____");
    //console.log("Pages: " + Object.keys(this.outgoingNodes).length);
    //console.log("outgoing %j", this.outgoingNodes);
    //console.log("incoming %j",this.incomingNodes);
    //console.log("probability %j",this.probabilityNodes);
};


//Calculate new weights 
// ----------
Pagerank.prototype.iterate = function(count) {
    var result = [];
    var resultHash={};
    var prob, ct, b, a, sum, res, max, min;

    //For each node, we look at the incoming edges and 
    //the weight of the node connected via each edge. 
    //This weight is divided by the total number of 
    //outgoing edges from each weighted node and summed to 
    //determine the new weight of the original node.
    for (b in this.probabilityNodes) {

        sum = 0;
        if( this.incomingNodes[b] ) {
            for ( a=0; a<this.incomingNodes[b].length; a++) {
                prob = this.probabilityNodes[ this.incomingNodes[b][a] ];
                ct = this.outgoingNodes[ this.incomingNodes[b][a] ].length;
                sum += (prob/ct) ;
            }
        }

        //determine if the new probability is within tolerance.
        res = this.coeff+this.linkProb*sum;
        max = this.probabilityNodes[b]+this.tolerance;
        min = this.probabilityNodes[b]-this.tolerance;   

        //if the result has changed push that result
        if (min <= res && res<= max) {
            resultHash[b]=res;
            result.push(res);
        }
    
        //update the probability for node *b*
        this.probabilityNodes[b]=res;
        //console.log(this.probabilityNodes[b]);
        //console.log(res);
    }

    //When we have all results (no weights are changing) we return via callback
    if (result.length == this.pageCount) {
        if( !(this.outgoingNodes instanceof Array)) {
            return this.callback(null, resultHash);
        }
        return this.callback(null, result);
    }
    
    //if debug is set, print each iteration
    if (this.debug) {
        this.reportDebug(count); 
    }
    
    ++count;
    return this.iterate(count);
};