[R] Absolute cumulative curve with ecdf/stepfun?

[Johannes Radinger]

Hi,

I have two variables ranging both from 0 to 1 (n=500 each).
Now I am interested in plotting them both in one plot (using ggplot2).

So far I used ecdf() (from an example I found with google) to get
values for the cumulatice distribution function which gives a relative
curve. I also want to do the same plot but using absolute cumulative
values instead of relative. Can that be done with ecdf or with stepfun()
to get values I can use to plot the curves?

Here a small example that shows the result with ecdf:

library(ggplot2)
library(reshape)

dftest1 <- data.frame(value=runif(1000,0,1),variable=rep(c("a","b"),c(500,500)))
dftest2 <- ddply(dftest1,.(variable),transform, ecd = ecdf(value)(value))

ggplot(dftest2,aes(x = value, y = ecd)) + 
		geom_line(aes(group = variable,colour = variable))

I'd like to replace the ecdf-function in ddply with a function that gives cumulative counts resp. the cumulative position of each observation, so that I get an absolute cumulative curve as a result? Is that understandable?

Thank you very much,

Johannes
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