ecdf
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
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