var arr = ['a', 'b', 'c', 'c', 'd','e', 'e',
'e', 'e', 'e', 'f', 'e', 'f', 'e',
'f', 'a', 'a', 'a', 'f', 'f', 'f'];

arr.join('').replace(/(.)()\1{2,}|./g, function(m) {
	return (m.length > 2) ? 
	    m.substr(0, 2) + '<span>' + m.substr(2) + '</span>' :
            m;
});

// My blog for more JavaScript funk: http://remysharp.com/