[j0hnik]

Poznakomlus,

function three(arr){
			return arr.filter((el, i)=> { 
				var s = 0; 
				while (i--) if (el == arr[i]) s++; 
				return (s>1&&s<=2); 
			});
		}
		console.log(three([5.6,435,5,6,5.3,5.6,5.6]));

для любых