[R] ecdf

[Dennis Murphy]

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?

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.
>