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 <gaw...@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
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______________________________________________
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David Winsemius, MD
Heritage Laboratories
West Hartford, CT
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