54 lines
1.2 KiB
JavaScript
54 lines
1.2 KiB
JavaScript
/*
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* Define some useful statistical functions on arrays of numbers
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*/
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Array.prototype.sum = function() {
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var i, sum = 0;
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for (i = 0; i < this.length; i++) {
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sum += this[i];
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}
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return sum;
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}
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Array.prototype.max = function() {
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return Math.max.apply(null, this);
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}
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Array.prototype.min = function() {
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return Math.min.apply(null, this);
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}
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Array.prototype.mean = function() {
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return this.sum() / this.length;
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}
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Array.prototype.average = Array.prototype.mean;
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Array.prototype.median = function() {
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var sorted = this.sort( function(a,b) { return a-b; }),
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len = sorted.length;
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if (len % 2) {
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return sorted[Math.floor(len / 2)]; // Odd
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} else {
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return (sorted[len/2 - 1] + sorted[len/2]) / 2; // Even
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}
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}
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Array.prototype.stdDev = function(sample) {
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var i, sumSqr = 0, mean = this.mean(), N;
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if (sample) {
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// Population correction if this is a sample
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N = this.length - 1;
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} else {
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// Standard deviation of just the array
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N = this.length;
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}
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for (i = 0; i < this.length; i++) {
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sumSqr += Math.pow(this[i] - mean, 2);
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}
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return Math.sqrt(sumSqr / N);
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}
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