Coding problem: How can I extract substring of function callwithin the function

Hi Joel,

Your objections are quite cogent, but I believe they are  
misdirected. I'm not at all interested in having my students ignore  
the existence of NA's and that's precisely why I'm not using the  
Default package as someone else suggested. But the mere existence of  
missing values in a data set doesn't make computation of the mean  
entirely useless -- why else would the na.rm option be available.

I agree: it's certainly not useless to calc the mean of a series of  
numbers while ignoring NA's.

If a student using my version of mean uses it to find the mean of a  
variable that has missing values, the function first prints a  
warning message and only then returns a value. Here's an example

length(x)

[1] 101

mean(x)

Warning: x has 3 missing values.
[1] 51.69388

Looks nice.

My only goal in this project has been to provide them with a  
somewhat friendlyR version of R. It was not conceived as part of a  
quest to improve my programming proficiency

I didn't think you were pursuing this to improve your programming  
proficiency from the outset, I just wanted to point out that you found  
a situation which you wanted to work around for (i) your precise use  
case. But it was because you were trying to solve (i) that you  
stumbled on (ii) and wanted to just know how one might do this for  
curiosity's sake and increase your proficiency (perhaps for some other  
use case in the future).

It was simply for reason (ii) that prompted me to say something only  
because you might not have seen your approach as potentially  
handicapping your students' (maybe subconcious(?)) pursuit of  
proficiency. I just wanted to point out that this is what you *might*  
be doing in the short term. Then again, it might not be.

Everyone has their own style of teaching, and it's your prerogative to  
do it as you see fit. I wouldn't presume to know which way is best, so  
good luck with the upcoming semester :-)

-steve

--
Steve Lianoglou
Graduate Student: Computational Systems Biology
  | Memorial Sloan-Kettering Cancer Center
  | Weill Medical College of Cornell University
Contact Info: http://cbio.mskcc.org/~lianos/contact