[igraph] vertex layout by date on a citation network

[fr510]

Dear Igraph helpers
I am working in R 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