ecdf

Hi,

On Sun, Oct 16, 2011 at 8:48 PM, gj <gawesh at gmail.com> wrote:

David is right. I am looking for the ecfd for fs$numstudents. The
other column is just an id.

I guess I don't know how to read the R documentation when it comes to functions.

looking at the documentation, i now notice that it says "Compute an
empirical cumulative distribution function and not a vector.

But still I would had assumed that in ecdf(x) ... the x is the argument.

ecdf() is the function you're calling.
x is your vector, for which you want the ECDF.

num.ecdf <- ecdf(fs$numstudents)

There. That's the ECDF.

But the ECDF is a *function* - that's what the F stands for, after all.

If you're looking for the percentiles for your data, you might try:

num.ecdf(fs$numstudents)

You might also try working the examples given in ?ecdf yourself, so
that you can see exactly what's going on before you try it with your
own data.

So ecdf(fs$numstudents)(unique(fs$numstudents))
? ? =============== ?==================
? ? ? ? ?function ? ? ? ? ? ? ? ? ? ? ? arguments

Yes? But I can't read that from the documentation? I suspect it has
something to those dots .... in the arguments which I don't
understand.

Yes.

That's the condensed version of what I just proposed, done in
one step, instead of two. The two-step version is definitely in
the help. It doesn't have anything to do with the ..., which simply allow
for other arguments to be passed.

Why it says usage ecdf(x) when it's clearly not the case?

I don't get it.

Clearly that is the case. ecdf(x) returns the empirical cumulative
distribution *function* of the vector of data x.

I'm not entirely sure what you think you should be getting. Perhaps
if you explained your expectations, the list would be able to help
you achieve them.

Sarah

Gawesh


On Sun, Oct 16, 2011 at 11:02 PM, David Winsemius
<dwinsemius at comcast.net> wrote:

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

David Winsemius, MD
Heritage Laboratories
West Hartford, CT

--
Sarah Goslee
http://www.stringpage.com
http://www.sarahgoslee.com
http://www.functionaldiversity.org