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Delete 'pages/students/2016/jan_holp/pagerank.js'

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Ján Holp 2021-01-05 08:36:40 +00:00
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commit 4604ea2951
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//"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);
};