[R] Again: Variable names in functions

[Heinz Tuechler]

At 11:48 17.02.2005 +0100, Uwe Ligges wrote:
>
>See argument "dnn" in ?table:
>
>
>   mytable2 <- function(x,y){
>     table(x, y, dnn = c(deparse(substitute(x)),
>                         deparse(substitute(y))))
>   }
>
>Uwe Ligges
>
>
>

Thank you for your hint. This is of course a good solution for the example.
Still I am looking for a more general solution, but it is not urgent.

Heinz Tüchler


>Heinz Tuechler wrote:
>
>> Hello,
>> 
>> still I have difficulties with variable names in functions. I know the
>> famous example form help for deparse/substitute but I will give a simpler
>> one to explain my problem.
>> I know from Reid Huntsinger (Tue, 8 Feb 2005 12:39:32 -0500) that:
>> "Semantically, R is pass-by-value, so you don't really have the names, just
>> the values. In implementation, though, R *does* pass names, in part at
least
>> in order to do "lazy evaluation". You can get them via "substitute" ; see
>> the help for that." 
>> 
>> The output of several functions does not make much sense, if these names do
>> not appear (e.g. parameter estimates in Cox-regression, ...)
>> Only to give a trivial example I show my problem with the table function.
>> 
>> As you know, if I call table as follows, the output is labelled properly.
>> 
>>>charly<-c(rep(1,3),rep(2,7));delta<-c(rep(1:2,5))
>>>table(charly, delta)
>> 
>>       delta
>> charly 1 2
>>      1 2 1
>>      2 3 4
>> If I define a trivial function to call table, the output is less
satisfying.
>> (Of course, I know that this function is useless.)
>> 
>>>mytable1<-function(x,y){table(x,y)}
>>>mytable1(charly, delta)
>> 
>>    y
>> x   1 2
>>   1 2 1
>>   2 3 4
>> If I define the function in the following way, it does what I wish, namely
>> it returns output equivalent to the simple call "table(charly, delta)".
>> 
>>>mytable2<-function(x,y){
>> 
>> +   cat("table(",as.symbol((deparse(substitute(x)))),
>> +   "," ,  as.symbol(deparse(substitute(y))),")\n",
>> +   file="temp",sep="",append=F)
>> +   eval(parse("temp",n=-1))
>> +                       }
>> 
>>>mytable2(charly, delta)
>>       delta
>> charly 1 2
>>      1 2 1
>>      2 3 4
>> 
>> I assume that there is a better way to solve this problem and I would be
>> happy about hints, where to find solutions in the documentation.
>> 
>> Thanks,
>> 
>> Heinz Tüchler
>> 
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>