R devel - Feb 2011 - matching symbols to objects

Hello,

I'm trying to access an object, given only its name as a symbol.  I cannot
figure out how to proceed.  Suppose I call substitute( ) on the expression
'x + 2':
> parse.tree <- substitute(x + 2);
The constituents of parse.tree are of type symbol and numeric:
> str(parse.tree[[1]])
symbol +
> str(parse.tree[[2]])
symbol x
> str(parse.tree[[3]])
num 2

Suppose that x is S4 object, and that I need to access a slot of that
object.  How can I do so, using only 'parse.tree' (or parse.tree coerced
into a list)?

Thanks, Patrick

	[[alternative HTML version deleted]]

Patrick,

Take a look at all.vars to start with  That will return the vars as
characters, from there you can use get to test/proceed.
> all.vars(parse.tree)
[1] "x"


Best,
Jeff

On Fri, Feb 4, 2011 at 1:37 PM, Patrick Leyshock <ngkbr8es at gmail.com>
wrote:
> Hello,
>
> I'm trying to access an object, given only its name as a symbol. ?I
cannot
> figure out how to proceed. ?Suppose I call substitute( ) on the expression
> 'x + 2':
>
>> parse.tree <- substitute(x + 2);
>
> The constituents of parse.tree are of type symbol and numeric:
>
>> str(parse.tree[[1]])
> symbol +
>
>> str(parse.tree[[2]])
> symbol x
>
>> str(parse.tree[[3]])
> num 2
>
> Suppose that x is S4 object, and that I need to access a slot of that
> object. ?How can I do so, using only 'parse.tree' (or parse.tree
coerced
> into a list)?
>
> Thanks, Patrick
>
> ? ? ? ?[[alternative HTML version deleted]]
>
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>


-- 
Jeffrey Ryan
jeffrey.ryan at lemnica.com

www.lemnica.com