[R] vertex ordering by date on a network diagram

[fr510 at york.ac.uk]

Dear R helpers I am working with a csv file containing data about a 
citation graph. This csv file contains a column with an id of the paper 
containing the citation the next with the id of the paper being cited and 
the third the date of publication (dd/mm/yyyy). I can create a directed 
network with vertices distributed randomly but cant seem to order them so 
that the oldest publications lie at the top and get younger moving down the 
graph. Any help would be very much appreciated Thanks