R devel - Mar 2007 - Symbol and Ellipsis problems

Hi Everyone,

When I have a load of functions which have various arguments passed
via the ellipsis argument it keeps on assigning them as symbol making
them unusable to the function.  My current work around involves using
do.call but this is rather cumbersome.

Does anyone know why it suddenly changes the types to symbol and if
there is a way to get the actual data pointed to by the symbol? (I
have tried eval but that does not work and most functions just treat a
symbol as a string).

( An example which shows the type conversion is given below with the
output - the key is the following "dataX=data" which makes the object
data passed as a symbol and not the actual data).

Many thanks

Tom

====EXAMPLE CODE===data=c(1,2,3,4,5,6,7,8,9);

x <- function( ... ) {
        args <- list();
        extras <- match.call(expand.dots = FALSE)$...;
        for( i in names(extras) ) {
                args[[ i ]] <- extras[[ i ]];
                print(args[[i]]);
                print(typeof(extras[[i]]));
        }


}

cat("TYPE OF DATA:");
print(typeof(data));
x(dataX=data);

On 3/20/2007 6:36 AM, Thomas McCallum wrote:
> Hi Everyone,
> 
> When I have a load of functions which have various arguments passed
> via the ellipsis argument it keeps on assigning them as symbol making
> them unusable to the function.  My current work around involves using
> do.call but this is rather cumbersome.
> 
> Does anyone know why it suddenly changes the types to symbol and if
> there is a way to get the actual data pointed to by the symbol? (I
> have tried eval but that does not work and most functions just treat a
> symbol as a string).
> 
> ( An example which shows the type conversion is given below with the
> output - the key is the following "dataX=data" which makes the
object
> data passed as a symbol and not the actual data).
match.call() doesn't evaluate the args, it just shows you the 
unevaluated call.  If you print your "extras" variable in your
function,
you'll see

$dataX
data

because you called the function with dataX=data.  If you'd called it as
x(dataY = 1+2) you'd see

1 + 2
[1] "language"

for the same reason.

If you want to evaluate the ... args, use list(...) instead of match.call.

Duncan Murdoch
> Many thanks
> 
> Tom
> 
> ====EXAMPLE CODE===> data=c(1,2,3,4,5,6,7,8,9);
> 
> x <- function( ... ) {
>         args <- list();
>         extras <- match.call(expand.dots = FALSE)$...;
>         for( i in names(extras) ) {
>                 args[[ i ]] <- extras[[ i ]];
>                 print(args[[i]]);
>                 print(typeof(extras[[i]]));
>         }
> 
> 
> }
> 
> cat("TYPE OF DATA:");
> print(typeof(data));
> x(dataX=data);
> 
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