R help - Apr 2010 - using get and paste in a loop to return objects for object names listed a strings

I am trying to create a heap of boxplots, by looping though a series of 
factors and variables in a large data.frame suing paste to constrcut the 
facto and response names from the colnames
I thought I could do this using get()
however it is not working what am I doing wrong?

thanks

Nevil Amos
> sp.codes=levels(data.all$CODE_LETTERS)
>
> for(spp in sp.codes) {
>
>
> data.sp=subset(data.all,CODE_LETTERS==spp)
>
> responses = colnames(data.all)[c(20,28,29,19)]
>  #if (spp=="BT") responses = colnames(data.all)[c(19,20,26:29)]
> groups=colnames   (data.all)[c(9,10,13,16,30)]
>
> data.sp=subset(data.all,CODE_LETTERS==spp)
> for (response in responses){
> for (group in groups){
> r<-get(paste("data.sp$",response,sep=""))
> g<-get(paste("data.sp$",group, sep=""))
> print (r)
> print(g)
>
> boxplot(r ~g)
> }}}
Error in get(paste("data.sp$", response, sep = "")) :
   object 'data.sp$Hb' not found

Nevil Amos wrote:
> I am trying to create a heap of boxplots, by looping though a series 
> of factors and variables in a large data.frame suing paste to 
> constrcut the facto and response names from the colnames
> I thought I could do this using get()
> however it is not working what am I doing wrong?
You don't give a reproducible example, this makes it hard to answer your 
question.

But not really in response to your question, take a look at histogram 
from the lattice package or geom_boxplot from the ggplot2 package. These 
functions can do all the work for you of drawing boxplots for a series 
of factors and variables in a large data.frame. This saves you a lot of 
time.

cheers,
Paul
>
> thanks
>
> Nevil Amos
>
>> sp.codes=levels(data.all$CODE_LETTERS)
>>
>> for(spp in sp.codes) {
>>
>>
>> data.sp=subset(data.all,CODE_LETTERS==spp)
>>
>> responses = colnames(data.all)[c(20,28,29,19)]
>>  #if (spp=="BT") responses =
colnames(data.all)[c(19,20,26:29)]
>> groups=colnames   (data.all)[c(9,10,13,16,30)]
>>
>> data.sp=subset(data.all,CODE_LETTERS==spp)
>> for (response in responses){
>> for (group in groups){
>> r<-get(paste("data.sp$",response,sep=""))
>> g<-get(paste("data.sp$",group, sep=""))
>> print (r)
>> print(g)
>>
>> boxplot(r ~g)
>> }}}
> Error in get(paste("data.sp$", response, sep = "")) :
>   object 'data.sp$Hb' not found
>
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-- 
Drs. Paul Hiemstra
Department of Physical Geography
Faculty of Geosciences
University of Utrecht
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