R devel - Nov 2006 - variable problem

Hi everyone,

I am not sure this is possible so I would be interested in your  
responses.  Say I have a variable 'v' with the string
"myargument" in and
I have a function 'f' that takes this argument as follows;

f <- function( myargument=5 ) {
   ... does something...
}

Is there anyway I can say something like;

f( v=10 ) such that it will be evaluated as f( myargument=10 ).

I presume there may be some use eval and substitute but if someone could  
point me in the right direction then that would be great.

The end idea is to have a list of m items, declared somewhere else,  which  
can be evaluated as particular arguments named after their list names

e.g

mylist <- list( "a"=1, "b"=2, "c"=3 )

which can be passed to a function taking arguments a,b, or c and it will  
be able to evaluate them accordingly :

long hand this would evaluate to something like
	f( a=mylist[["a"]] );
	f( b=mylist[["b"]] );
	f( c=mylist[["c"]] );

but I would have actually rewritten something like
	for ( myvar in names( mylist ) ) {
		f( some_clever_substitution_to_act_as_argument(myvar) = mylist[[ myvar  
]] );	
	}

I hope I have explained myself clearly enough, if not please say so and I  
will try and give a better example.

Many thanks for your help

Tom



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Dr. Thomas McCallum
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On Tuesday 07 November 2006 3:28 pm, Tom McCallum wrote:
> Hi everyone,
Hi Tom, 

    Would this snippet work:

    for(i in 1:length(mylist))do.call(f, mylist[i])

    On the other hand it is not easy to see why you would want to call the 
same function with differently named arguments - perhaps what you are really 
trying to do has a different (and better) solution ?

                       best

                          Vladimir Dergachev
>
> I am not sure this is possible so I would be interested in your
> responses.  Say I have a variable 'v' with the string
"myargument" in and
> I have a function 'f' that takes this argument as follows;
>
> f <- function( myargument=5 ) {
>    ... does something...
> }
>
> Is there anyway I can say something like;
>
> f( v=10 ) such that it will be evaluated as f( myargument=10 ).
>
> I presume there may be some use eval and substitute but if someone could
> point me in the right direction then that would be great.
>
> The end idea is to have a list of m items, declared somewhere else,  which
> can be evaluated as particular arguments named after their list names
>
> e.g
>
> mylist <- list( "a"=1, "b"=2, "c"=3 )
>
> which can be passed to a function taking arguments a,b, or c and it will
> be able to evaluate them accordingly :
>
> long hand this would evaluate to something like
> 	f( a=mylist[["a"]] );
> 	f( b=mylist[["b"]] );
> 	f( c=mylist[["c"]] );
>
> but I would have actually rewritten something like
> 	for ( myvar in names( mylist ) ) {
> 		f( some_clever_substitution_to_act_as_argument(myvar) = mylist[[ myvar
> ]] );
> 	}
>
> I hope I have explained myself clearly enough, if not please say so and I
> will try and give a better example.
>
> Many thanks for your help
>
> Tom