function(ar) {
let sq = ar.map((v) => (v * v));
let s = sq.reduce((a, v) => (a + v));
return Math.sqrt(s / ar.length);
}
function(ar) {
let sq = ar.map((v) => (v * v));
let s = sq.reduce((a, v) => (a + v));
return Math.sqrt(s / ar.length);
}