var stdDev = [1,2,7,2....].stddev();
Array.reduce.sum = function sum() {
    var sum = this.reduce(function(previous, current) {
        return previous + current;
    });
    return sum;
};
Array.prototype.square = function squareArray() {
    return this.map(function(x) {
        return x * x;
    });
};
Array.prototype.mean = function mean() {
    return this.sum() / this.length;
};
Array.prototype.standardDeviation = function standardDeviation() {
var mean = this.mean();
    var int1 = this.map(function(n) {
        return n - mean;
    });
    var int2 = int1.square();
    var int3 = Math.sqrt(int2.sum() / mean.length);
};

//Naley nada krtsz nazw
Array.prototype.stddev = Array.prototype.standardDeviation;