JS Statistics Functions


Javascript do not have an object or package that specifically handling statistics. Here are some javascript scipts of variance, stardard deviation, standard error, mean, median calculations.


Mean of a number array

//Check whether is a number or not
function isNum(args)
{
	args = args.toString();
	if (args.length == 0) return false;
	for (var i = 0; i<args.length; i++)
	{
		if ((args.substring(i,i+1) < "0" || args.substring(i, i+1) > "9") 
		    && args.substring(i, i+1) != "." && args.substring(i, i+1) != "-")
		{return false;}
	}
	return true;
}
//calculate the mean of a number array
function mean(arr)
{
	var len = 0;
	var sum = 0;
	for(var i=0;i<arr.length;i++)
	{
		if (arr[i] == ""){}
		else if (!isNum(arr[i]))
		{
			alert(arr[i] + " is not number!");
			return;
		}
		else
		{
			len = len + 1;
			sum = sum + parseFloat(arr[i]);
		}
	}
	return sum / len;
}


Variance of a number array

function variance(arr)
{
	var len = 0;
	var sum=0;
	for(var i=0;i<arr.length;i++)
	{
		if (arr[i] == ""){}
		else if (!isNum(arr[i]))
		{
			alert(arr[i] + " is not number, Variance Calculation failed!");
			return 0;
		}
		else
		{
			len = len + 1;
			sum = sum + parseFloat(arr[i]);
		}
	}
	var v = 0;
	if (len > 1)
	{
		var mean = sum / len;
		for(var i=0;i<arr.length;i++)
		{
			if (arr[i] == ""){}
			else { v = v + (arr[i] - mean) * (arr[i] - mean); }
		}
		return v / len;
	}
	else { return 0; }
}


Get the largest and smallest number of a number array

//Get the largest number of a number array
function max(arr)
{
	var max = -99999;
	for(var i=0;i<arr.length;i++)
	{
		if (arr[i] == ""){}
		else if (!isNum(arr[i]))
		{
			alert(arr[i] + " is not number!");
			return;
		}
		else
		{
			if (i == 0) {max = arr[i];}
			else if (max < arr[i]) {max = arr[i];}
		}
	}
	return max;
}
//Get the smallest number of a number array
function min(arr)
{
	var min = 99999;
	for(var i=0;i<arr.length;i++)
	{
		if (arr[i] == ""){}
		else if (!isNum(arr[i]))
		{
			alert(arr[i] + " is not number!");
			return;
		}
		else
		{
			if (i == 0) {min = arr[i];}
			else if (min > arr[i]) {min = arr[i];}
		}
	}
	return min;
}


Standard deviation (SD) and standard error (SE)

//Standard deviation
var sd = Math.sqrt(variance(arr));
//Standard error
var se = Math.sqrt(variance(arr)/(arr.length-1));


median of a number array

function median(arr)
{
	arr.sort(function(a,b){return a-b});
	var median = 0;
	if (arr.length % 2 == 1)
	{
		median = arr[(arr.length+1)/2 - 1];
	}
	else
	{
		median = (1 * arr[arr.length/2 - 1] + 1 * arr[arr.length/2] )/2;
	}
	return median;
}




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