Use of variables to reference to objects

Hi,

I'm new to R and looking for a way to use a variable to reference to an
object.

I'm plotting several graphs on top of each other and want to do this by
a for loop. The field I want to graph have names like a1,a2,a3, ...
I can't figure out how to get this working:

It should look like this:
lines(spectral$Wavelength,paste("spectral$a",j,sep=""),col=j)

but the "paste()" does not seem to work in this context.

Any help?

1. I suggest to generate a list "a", which can be indexed with a[[j]],
so you don't need any sophisticated mechanism to reference to your
objects.

2. Answer of your question: Use get().

Uwe Ligges
-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
Send "info", "help", or "[un]subscribe"
(in the "body", not the subject !)  To: r-help-request at stat.math.ethz.ch
_._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._

Hi,

I'm new to R and looking for a way to use a variable to reference to an
object.

I'm plotting several graphs on top of each other and want to do this by
a for loop. The field I want to graph have names like a1,a2,a3, ...
I can't figure out how to get this working:

It should look like this:
lines(spectral$Wavelength,paste("spectral$a",j,sep=""),col=j)

but the "paste()" does not seem to work in this context.

No, it wouldn't.  That gives you the name of the variable, not the
variable.

Probably the simplest solution is either
   lines(spectral$Wavelength, spectral[[paste("a",j,sep="")]],col=j)
but there's also
   lines(spectral$Wavelength,get(paste("spectral$a",j,sep="")),col=j)
and various others

	-thomas

-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
Send "info", "help", or "[un]subscribe"
(in the "body", not the subject !)  To: r-help-request at stat.math.ethz.ch
_._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._

The "get" function is the usual answer to this sort of question, but is 
not right
for this particular case.  Actually, a simpler answer works.

lines(spectral$Wavelength, spectral[[ paste("a", j, sep="") ]], col=j)

Using "get" would want to get objects with names like "spectral$a1"
rather than the "a1" component of "spectral".



Patrick Burns
patrick at burns-stat.com
+44 (0) 208 525 0696
http://www.burns-stat.com/    (new home of S Poetry)

Hi,

I'm new to R and looking for a way to use a variable to reference to 
an object.

I'm plotting several graphs on top of each other and want to do this 
by a for loop. The field I want to graph have names like a1,a2,a3, ...
I can't figure out how to get this working:

It should look like this:
lines(spectral$Wavelength,paste("spectral$a",j,sep=""),col=j)

but the "paste()" does not seem to work in this context.

Any help?

Kind regards,

Kris

-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
Send "info", "help", or "[un]subscribe"
(in the "body", not the subject !)  To: r-help-request at stat.math.ethz.ch
_._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._