R devel - Jul 2010 - Defining a method that behaves like '$'?

Hi,

is there a way to define a method say '$$' that would behave like
'$'
and allow calls like 'a$$name'?
Thanks.

Renaud

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Renaud Gaujoux
Computational Biology - University of Cape Town
South Africa


 

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Le 09/07/10 14:18, Renaud Gaujoux a ?crit :
>
> Hi,
>
> is there a way to define a method say '$$' that would behave like
'$'
> and allow calls like 'a$$name'?
> Thanks.
>
> Renaud
No. This is not grammatically valid syntax:

 > parse( text = 'a$$name' )
Erreur dans parse(text = "a$$name") : '$' inattendu(e) dans
"a$$"


But you can define custom methods for $.

setClass( "Foo", representation( n = "integer" ) )
setMethod( "$", "Foo", function(x, name ){
	function( ) rnorm( x at n )
} )
foo <- new( "Foo", n = 10L )
foo$bla( )


Romain

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On 09/07/2010 8:18 AM, Renaud Gaujoux wrote:
> Hi,
>
> is there a way to define a method say '$$' that would behave like
'$'
> and allow calls like 'a$$name'?
No, the parser handles a fixed syntax, and that expression is not 
legal.  You could do it with

a %$$% name

using the infix operator syntax.  (I think the description in the R 
Language Definition suggests this is not legal, since $$ is not a valid 
name, but it does currently work and that's unlikely to change.)

Duncan Murdoch