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;
}
```