R help - Jul 2013 - memory allocation and management question

dear R experts:   I am curious again about R memory allocation strategies.
 Consider an intentionally inefficient program:

ranmatme <- function( lx, rx ) {
    m <- matrix(NA, nrow=lx, ncol=rx)
    for (li in 1:rx) {
        cat("\tLag i=", li, "object size=", object.size(m),
"\n")
        m[,li] <- rnorm(lx)
    }
    m
}

v <- ranmatme( 1024*1024*128, 3 )


[1] on the first cat, the object size is only 1.6GB, which is half the size
of the 3.2GB that it is on the 2nd and 3rd call.  why?

[2] I tried to monitor the linux memory allocation in another window.  I
could be completely wrong, but it seems that upon function exit, memory
usage spikes briefly.  it is almost as if there was an explicit copy of m
into v, and both had to exist simultaneously for a moment in time.  is this
the case?  (if so, is there a way to return and assign just the reference?
 I may be blanking here---maybe the answer is obvious.)

regards,

/iaw
----
Ivo Welch (ivo.welch@gmail.com)

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I can give you the answer to #1.  If you had put a "print(str(m))" you
would have seen that initially the matrix was setup as logical which
requires 4 bytes per element.  On the first assignment of a numeric, the
mode of 'm' is changed to numeric which requires 8 bytes per element;
that
is the reason for the "doubling".


On Mon, Jul 15, 2013 at 6:50 PM, ivo welch
<ivo.welch@anderson.ucla.edu>wrote:
> dear R experts:   I am curious again about R memory allocation strategies.
>  Consider an intentionally inefficient program:
>
> ranmatme <- function( lx, rx ) {
>     m <- matrix(NA, nrow=lx, ncol=rx)
>     for (li in 1:rx) {
>         cat("\tLag i=", li, "object size=",
object.size(m), "\n")
>         m[,li] <- rnorm(lx)
>     }
>     m
> }
>
> v <- ranmatme( 1024*1024*128, 3 )
>
>
> [1] on the first cat, the object size is only 1.6GB, which is half the size
> of the 3.2GB that it is on the 2nd and 3rd call.  why?
>
> [2] I tried to monitor the linux memory allocation in another window.  I
> could be completely wrong, but it seems that upon function exit, memory
> usage spikes briefly.  it is almost as if there was an explicit copy of m
> into v, and both had to exist simultaneously for a moment in time.  is this
> the case?  (if so, is there a way to return and assign just the reference?
>  I may be blanking here---maybe the answer is obvious.)
>
> regards,
>
> /iaw
> ----
> Ivo Welch (ivo.welch@gmail.com)
>
>         [[alternative HTML version deleted]]
>
> ______________________________________________
> R-help@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>


-- 
Jim Holtman
Data Munger Guru

What is the problem that you are trying to solve?
Tell me what you want to do, not how you want to do it.

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