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function shuffle(a){ var aa = new Array(a.length); aa[0] = a[0]; for (var i = 1; i < a.length; i++) { var j = Math.floor( Math.random() * i ); aa[i] = aa[j]; aa[j] = a[i]; } return aa; } function sample(a, n) { var aa = shuffle(a); return aa.slice(0,n); }