[R] ecdf

[gj]

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