R help - Sep 2011 - (no subject)

The code looks like this:
L1=list(a=1,b=2,c=3)
f1=as.factor(c)
L1[[f1]] returns 1

What happens if we give a factor as an index at a list?

	[[alternative HTML version deleted]]

Is this meant to be a follow up to something?

In short, the answer to your question is how factors are encoded as integers
in R. If you run something similar to this code (except that actually runs)
you'll note that as.numeric(f1) = 1.

Michael

On Wed, Sep 7, 2011 at 5:04 AM, Varsha Agrawal
<varsha.nipfp@gmail.com>wrote:
> The code looks like this:
> L1=list(a=1,b=2,c=3)
> f1=as.factor(c)
> L1[[f1]] returns 1
>
> What happens if we give a factor as an index at a list?
>
>        [[alternative HTML version deleted]]
>
> ______________________________________________
> R-help@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.
>
	[[alternative HTML version deleted]]

On Sep 7, 2011, at 6:04 AM, Varsha Agrawal wrote:
> The code looks like this:
> L1=list(a=1,b=2,c=3)
> f1=as.factor(c)
> L1[[f1]] returns 1
>
> What happens if we give a factor as an index at a list?
In a virgin session of R there would be no 'c' for the second line to  
work with. And since 'c' is a function you would probably get an error.

 > L1=list(a=1,b=2,c=3)
 > f1=as.factor(L1$c)
 > f1
[1] 3
Levels: 3
 > L1[[f1]] #returns 1
[1] 1

It is ill-mannered to attach an object and not tell us that was done.  
So why is "3" as an index returning 1? because the internal  
representation of a factor was used by the parser. Furthermore even  
the usual dodge of wrapping as.character around f1 will not succeed  
since f1 didn't record where it got the value of "3", and there is
no
L1["3"] or L1[["3"]] only an L1[[3]] and an L1[3]

 > L1[[as.character(f1)]]
NULL

So you need the "full-court [factor] press":

 > L1[[as.numeric(as.character(f1))]]
[1] 3


>
> 	[[alternative HTML version deleted]]
>
> ______________________________________________
> 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
West Hartford, CT