R-devel Digest, Vol 83, Issue 2

On 1/2/10 11:41 PM, Romain Francois wrote:

On 01/02/2010 11:12 PM, Duncan Murdoch wrote:

On 02/01/2010 3:16 PM, Laurent Gautier wrote:

On 1/2/10 8:53 PM, Duncan Murdoch wrote:

Simon Urbanek wrote:

On Jan 2, 2010, at 12:17 PM, Laurent Gautier wrote:

On 1/2/10 5:56 PM, Duncan Murdoch wrote:

On 02/01/2010 11:36 AM, Laurent Gautier wrote:

[Disclaimer: what is below reflects my understanding from reading
the
R source, others will correct where deemed necessary]

On 1/2/10 12:00 PM, r-devel-request at r-project.org wrote:

(...)

(...)

I don't think I would want to review such a patch (I don't know the
memory manager well, I don't know that there is really a case where it
matters enough to be worth doing), so I'd say if you don't get a message
from a core member volunteering to do so, you should assume it won't be
accepted. But that doesn't mean you shouldn't write the code for your
own internal use and edification, and if you can put together a demo
that shows it really makes a big difference in a realistic situation,
you might get a different response.

Duncan Murdoch

 From what I understand, this has little to do with the memory manager,
and resumes to the simple problem "how to remove an object from a list".

I would generalize even further, up to: "how to make a tail recursion 
into an interation" (and that often boils down to writing a for loop - 
little edification to get from it, I suppose... one probably wants to 
write it to see it included).

I see below that you are living up to the enthusiasm claimed, and had a 
shot at it (and even did benchmark to demonstrate the expected benefit - 
impressive).

Let's see what happens with it...


L.

Something like this, using the amazing inline and inspect packages:

require( inline )
require( inspect )

remover <- cfunction(signature( list = "language", object =
"environment" ), '
if( !isNull( list ) ){
SEXP x = list ;
SEXP y ;
while( CAR(x) != object && CADR(x) != R_NilValue ){
y = x ;
x = CDR(x) ;
}
if( CAR(x) == object ) SETCDR(y, CDR(x) ) ;
}
return list ;
', Rcpp=FALSE, verbose=FALSE )

e <- new.env()
call <- call( "foo", e, e, 1:10, 3 )
call
# inspect( call )
result <- remover( call ,e )
result
# inspect( result )

gives this :

foo(10, <environment>, 0, <environment>, 1)
@0x9f4e0d0 06 LANGSXP [NAM(2)]
@0x9f4e204 01 SYMSXP [] "foo"
@0xa907b78 14 REALSXP [NAM(2)] (len=1, tl=1763713056)
@0x9f4d564 04 ENVSXP [NAM(1)]
FRAME:
@0x9e94a10 00 NILSXP [MARK,NAM(2)]
ENCLOS:
@0x9eb7b4c 04 ENVSXP [MARK,NAM(2),GP(0x8000)]
HASHTAB:
@0x9e94a10 00 NILSXP [MARK,NAM(2)]
@0xa907b58 14 REALSXP [NAM(2)] (len=1, tl=1936941344)
@0x9f4d564 04 ENVSXP [NAM(1)]
FRAME:
@0x9e94a10 00 NILSXP [MARK,NAM(2)]
ENCLOS:
@0x9eb7b4c 04 ENVSXP [MARK,NAM(2),GP(0x8000)]
HASHTAB:
@0x9e94a10 00 NILSXP [MARK,NAM(2)]
@0xa907b38 14 REALSXP [NAM(2)] (len=1, tl=543908709)
NULL
==================
foo(10, 0, <environment>, 1)
@0x9f4e0d0 06 LANGSXP [NAM(2)]
@0x9f4e204 01 SYMSXP [] "foo"
@0xa907b78 14 REALSXP [NAM(2)] (len=1, tl=1763713056)
@0xa907b58 14 REALSXP [NAM(2)] (len=1, tl=1936941344)
@0x9f4d564 04 ENVSXP [NAM(2)]
FRAME:
@0x9e94a10 00 NILSXP [MARK,NAM(2)]
ENCLOS:
@0x9eb7b4c 04 ENVSXP [MARK,NAM(2),GP(0x8000)]
HASHTAB:
@0x9e94a10 00 NILSXP [MARK,NAM(2)]
@0xa907b38 14 REALSXP [NAM(2)] (len=1, tl=543908709)
NULL



so it boils down to this as a replacement to RecursiveRelease :

/**
* Removes the first instance of object with the list
*/
static SEXP RemoveFromList( SEXP object, SEXP list){
if( !isNull( list ) ){
SEXP x = list ;
SEXP y ;
while( CAR(x) != object && CADR(x) != R_NilValue ){
y = x ;
x = CDR(x) ;
}
if( CAR(x) == object ) SETCDR(y, CDR(x) ) ;
}
return list ;
}


Romain