ecdf
On Oct 16, 2011, at 3:53 PM, Dennis Murphy wrote:
Hi: I don't understand what you're attempting to do. Wouldn't courseid be a categorical variable with a numeric label? If that is so, why are you trying to compute an EDF? An EDF computes cumulative relative frequency of a random variable, which by definition is numeric. If we were talking about EDFs for a distribution of student course grades on a numeric point system by course, that would make some sense, but I don't see how the course IDs themselves qualify as being on an interval scale of measurement. Could you clarify your intent?
Huh? gawesh asked for ecdf on numstrudents (not courseid) ... pretty clearly a numeric value for which an ECDF should make sense. -- David.
> Dennis > > On Sun, Oct 16, 2011 at 8:31 AM, gj <gawesh at gmail.com> wrote: >> Hi, >> Newbie here. I read the R for Beginners but i still don't get this. >> >> I have the following data (this is just an example) in a CSV file: >> >> courseid numstudents >> 101 209 >> 141 13 >> 246 140 >> 263 8 >> 321 10 >> 361 10 >> 364 28 >> 365 25 >> 366 23 >> 367 34 >> >> I load my data using: >> >> fs<-read.csv(file="C:\\num_students_inallmodules.csv",header=T, >> sep=',') >> >> I want to get the ecdf. So, I looked at the ?ecdf which says >> usage:ecdf(x) >> >> So I expected ecdf(fs$numstudents) to work >> >> Instead it just returned: >> Call: ecdf(fs$numstudents) >> x[1:210] = 1, 2, 3, ..., 3717, 4538 >> >> After Googling, got this to work: >> ecdf(fs$numstudents)(unique(fs$numstudents)) >> >> But I don't understand why if the ?ecdf says usage is ecdf(x) ... I >> need to use ecdf(fs$numstudents)(unique(fs$numstudents)) to get this >> to work? >> >> Can somebody explain this to me? >> >> Regards >> Gawesh >> >> ______________________________________________ >> R-help at r-project.org mailing list >> https://stat.ethz.ch/mailman/listinfo/r-help >> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html >> and provide commented, minimal, self-contained, reproducible code. >> > > ______________________________________________ > R-help at r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. David Winsemius, MD Heritage Laboratories West Hartford, CT