Cumulative Function

I was wandering if anyone cold advise me on a good algorithm to turn a set of
data from its original for into its cumulative form.  I have written a piece
of code that takes the data and does essentially what a histogram function
would do, except add to the new bin the sum in the previous bin.  Once that
is done I divide by the frequency in the last bin plus 1.  I know the ecdf()
function exists in R, but I want to use it to fit the cumulative
distributions to the data and ecdf() produces a non-subscriptable vector and
so fitdistr() cannot be used on it.

Thanks for any help you can give
Mark Miller