//  returns an array of every freq'th item
// _rtl starts the sampling from the right-side of the array
function cull (list, freq, _rtl) {
  list = _.isArray(list) ? list.slice(0) : [];
  freq = freq || 1;

  if (_rtl) {
    list.reverse();
  }

  list = _.filter(list, function (val, i) {
    if (i%freq === 0) {
      return val;
    }
  });

  return _rtl ? list.reverse() : list;
}