Just upload the files to the proper user directory as they come in. Stuffing everything into one directory is messy and decreases file system efficiency for large numbers of files (since it has to find inside ux files rather than u directories and then x files). Plus, depending on your file system, you may not be able to handle more than a certain number of files per directory anyway.

Or if you have to work in batch, just move the files from /userdate.txt to /user/date.txt.