[R] Again: Variable names in functions

[Peter Dalgaard]

Heinz Tuechler <tuechler at gmx.at> writes:

> 
> Thank you, this method works well. One step further I am again using
> parse(), but maybe there is a better solution for that situation too.
> The example would be a function, where I pass the variable name as string
> instead of the name. The motivation for this is that it seems easier to
> handle if I want to pass several variables (i.e. a vector of variable
> names) to the function (as I learned recently from this help-list). 
> In this case I have to use get(). In the case of calling table() the
> variable name disappeares.
> 
> > alpha<-c(rep(1:5,10))
> > name.alpha<-"alpha"
> > mytable1<-function(x){print(table(get(x)))}
> > mytable1(name.alpha)
> 
>  1  2  3  4  5 
> 10 10 10 10 10 
> 
> If I use eval(parse()) instead, it works as expected. I tried several
> combinations of eval() and substitute() but I did not find a solution.
> Is there a similar "trick"?
> 
> > mytable2<-function(x){
> +   string<-paste("print(table(",as.symbol(x),"))")
> +   eval(parse(text=string))}
> > mytable2(name.alpha)
> alpha
>  1  2  3  4  5 
> 10 10 10 10 10 

You're almost there: 

eval(substitute(table(e),list(e=as.symbol(x))))

(or eval.parent, which() safeguards somewhat against scoping issues)

-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
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