R help - Apr 2009 - Evaluation of an expression as function argument

Dear R-users,

I would like to know if is it possible to set a function argument as an 
evaluated expression. I have tried several syntaxes, including the 
following example, but could not get it anything to run. The plot 
function is used here but I would like to later apply the same approach 
to other functions.

##########################
items <- c(expression(col=2),expression(pch=2))

for (in in seq(2)) {
  plot(1:10, eval(items[i]))
}
##########################

Thanks in advance for your input.

Sebastien

Try this,
> items <- c(list(col=2),list(pch=2))
>
> par(mfrow=c(2, 1))
> for (ii in seq(2)) {
>  do.call(function(x, y, ... ) plot(1:10, ...), items[ii])
> }
?do.call


HTH,

baptiste


On 29 Apr 2009, at 19:30, Sebastien Bihorel wrote:
> Dear R-users,
>
> I would like to know if is it possible to set a function argument as  
> an
> evaluated expression. I have tried several syntaxes, including the
> following example, but could not get it anything to run. The plot
> function is used here but I would like to later apply the same  
> approach
> to other functions.
>
> ##########################
> items <- c(expression(col=2),expression(pch=2))
>
> for (in in seq(2)) {
>  plot(1:10, eval(items[i]))
> }
> ##########################
>
> Thanks in advance for your input.
>
> Sebastien
>
> ______________________________________________
> 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.
_____________________________

Baptiste Augui?

School of Physics
University of Exeter
Stocker Road,
Exeter, Devon,
EX4 4QL, UK

Phone: +44 1392 264187

http://newton.ex.ac.uk/research/emag

Sebastien Bihorel wrote:
> Dear R-users,
> 
> I would like to know if is it possible to set a function argument as an 
> evaluated expression. I have tried several syntaxes, including the 
> following example, but could not get it anything to run. The plot 
> function is used here but I would like to later apply the same approach 
> to other functions.
> 
> ##########################
> items <- c(expression(col=2),expression(pch=2))
>
> for (in in seq(2)) {
>  plot(1:10, eval(items[i]))
> }
> ##########################
Way 1:

for(i in seq(2))
   do.call("plot", c(list(1:10), as.list(items[i])))


Way 2 is perhaps easier for you:


items <- list(col=2, pch=2)
for (i in seq(2))
   do.call("plot", c(list(1:10), items[i]))


Ways 3...n up to others...


Uwe Ligges



> 
> Thanks in advance for your input.
> 
> Sebastien
> 
> ______________________________________________
> 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.

Thanks Uwe and Baptiste

*Sebastien Bihorel, PharmD, PhD*
PKPD Scientist
Cognigen Corp
Email: sebastien.bihorel at cognigencorp.com 
<mailto:sebastien.bihorel at cognigencorp.com>
Phone: (716) 633-3463 ext. 323


Uwe Ligges wrote:
>
>
> Sebastien Bihorel wrote:
>> Dear R-users,
>>
>> I would like to know if is it possible to set a function argument as 
>> an evaluated expression. I have tried several syntaxes, including the 
>> following example, but could not get it anything to run. The plot 
>> function is used here but I would like to later apply the same 
>> approach to other functions.
>>
>> ##########################
>> items <- c(expression(col=2),expression(pch=2))
>>
>> for (in in seq(2)) {
>>  plot(1:10, eval(items[i]))
>> }
>> ##########################
>
> Way 1:
>
> for(i in seq(2))
>   do.call("plot", c(list(1:10), as.list(items[i])))
>
>
> Way 2 is perhaps easier for you:
>
>
> items <- list(col=2, pch=2)
> for (i in seq(2))
>   do.call("plot", c(list(1:10), items[i]))
>
>
> Ways 3...n up to others...
>
>
> Uwe Ligges
>
>
>
>
>>
>> Thanks in advance for your input.
>>
>> Sebastien
>>
>> ______________________________________________
>> 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.