[R] ecdf

[David Winsemius]

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
>>
>> ______________________________________________
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>> 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