[R] Extracting variables with a given prefix in the parent environment

[Duncan Murdoch]

On 20/10/2008 2:06 AM, erwann rogard wrote:
> hi,
> 
> get.vars.name.prefix<-function(prefix){
>  result<-list()
>  len<-nchar(prefix)
>  var.names<-ls(name=1,pattern=prefix) #name=1 probably wrong option
>  print(var.names)
>  for(i in 1:length(var.names)){
>   name<-var.names[i]
>   field<-substr(name,len+1,nchar(name))
>   result[[field]]<-get(name)
>  }
>  result
> }
> 
> for example
> x.1<-1
> x.2<-2
> get.vars.name.prefix("x.") should return 1,2
> 
> this does not work if i call if from within another function:
> 
> g<-function(){
>   x.1<-1
>   x.2<-2
>   get.vars.name.prefix("x.") # should return 1,2, nothing else
> }
> 
> i would like the environment specified within ls(...) to be that of the body
> of the function that calls get.vars.name.prefix. apparently name=1 is
> probably not the right option.

Use ls(name=parent.frame(), pattern=...)

And be careful about the pattern:  it's a regular expression, so you 
would need to start with a caret "^" to guarantee that it occurs at the 
start of the name.

Duncan Murdoch