What do you really want to do? One common problem with postings in these forums is when the original poster self-edits themselves too much, and in an apparent attempt to avoid boring us to death, ends up providing too little detail.
Do you have two dimensions of data stored in a one-D structure – in other words: Is your data a series of four-element-long subsequences? What do you want as a result? A list of all of the individual four-element strings? Just the first four, as your posting literally stated?
Stan’s response appears to be addressing that; the literal interpretation of what you asked for;
Thanks for the comment Brian. With the @Middle, how should I set the endstring or numberchars? Since the data in the “list” field are concatenated, with ~ as a separator, how can I specify the number of element to return from?