[Rd] modifying large R objects in place

[Byron Ellis]

For the most part, doing anything to an R object result in it's
duplication. You generally have to do a lot of work to NOT copy an R
object.

On 9/26/07, Petr Savicky <savicky at cs.cas.cz> wrote:
> I have a C function, which performs a transformation
> of a large integer matrix. The matrix may be of size 1.6GB,
> so I can have only one copy in RAM and have to modify it
> in place. This is possible using .Call and works fine. For
> debugging, I need two copies of a smaller matrix and modify only
> one of them. This may also be done, for example, by
>   A <- some integer matrix
>   B <- A + as.integer(0)
>   .Call("transform", A)
> Then, B is still the original and A is the transformed one.
> Up to now, I do not have any real problem with this, but there
> are things, which could help me. Namely the following ones:
>
> 1. Is there a general way to duplicate an R object on the
>    level of R language? I would use it instead of
>       B <- A + as.integer(0)
>    Looking for the keywords "duplicate" and "copy" in help pages
>    and R-exts did not find what I need.
>
> 2. Is there a way how a C function can verify that its
>    argument does not share data with other objects?
>    I included a test of NAMED(A) in my C function, but I do
>    not know, whether it may be used for the purpose which I need.
>    I did not find a way how to generate an R object with
>    NAMED equal 0. Is this possible on the level of R language?
>    If yes, I will require that the argument passed to my
>    function is generated in this way and the function
>    will refuse to modify it if it is not so.
>    The documentation suggests to call "duplicate", if the
>    data are shared, but I cannot afford this due to memory.
>    So, I can only stop if NAMED is not 0.
>
> I appreciate, if anybody could give me advice on the above things.
>
> Petr Savicky.
>
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>


-- 
Byron Ellis (byron.ellis at gmail.com)
"Oook" -- The Librarian