module.exports = stdev;

function stdev(arr) {

if (!Array.isArray(arr)) {

arr = [].slice.call(arguments);

}

if (!arr.length || arr.length < 2) {

throw new Error('less than one value was passed to `standard deviation`');

}

var sum = 0;

var len = arr.length;

for (var i = 0; i < len; i++) {

var n = arr[i];

if (!Number.isFinite(n)) {

throw new Error(

'all values passed to `standard deviation` must be numeric'

);

}

sum += n;

}

var mean = sum / len;

var acc = 0;

for (var i = 0; i < len; i++) {

var n = arr[i];

acc += (n - mean) * (n - mean);

}

return Math.sqrt(acc / (len - 1));

}