Gabor Grothendieck wrote:
>
> Passing by value does not necessarily mean physical copying. Check out
> this:
>
>> x <- matrix(1:1000^2, 1000, 1000)
>> gc()
> used (Mb) gc trigger (Mb) max used (Mb)
> Ncells 114520 3.1 350000 9.4 350000 9.4
> Vcells 577124 4.5 1901092 14.6 1577448 12.1
>> f <- function(x) { y <- max(x); print(gc()); y }
>> f(x)
> used (Mb) gc trigger (Mb) max used (Mb)
> Ncells 114560 3.1 350000 9.4 350000 9.4
> Vcells 577133 4.5 1901092 14.6 1577448 12.1
> [1] 1000000
>> R.version.string
> [1] "R version 2.10.1 (2009-12-14)"
>> win.version()
> [1] "Windows Vista (build 6002) Service Pack 2"
>
Yes, but you might pay a price in memory if you start altering values in x
within the function:
> x <- matrix(1:1000^2, 1000, 1000)
> gc(TRUE)
Garbage collection 5 = 1+0+4 (level 2) ...
3.2 Mbytes of cons cells used (34%)
4.5 Mbytes of vectors used (30%)
used (Mb) gc trigger (Mb) max used (Mb)
Ncells 119554 3.2 350000 9.4 350000 9.4
Vcells 578542 4.5 1902416 14.6 1581475 12.1
> f <- function(x) { x[100,100]<-2; print(gc(TRUE)) }
> f(x)
Garbage collection 7 = 1+0+6 (level 2) ...
3.2 Mbytes of cons cells used (34%)
12.1 Mbytes of vectors used (60%)
used (Mb) gc trigger (Mb) max used (Mb)
Ncells 119634 3.2 350000 9.4 350000 9.4
Vcells 1578573 12.1 2629025 20.1 2078567 15.9
> R.version.string
[1] "R version 2.10.1 (2009-12-14)"
-Charlie
-----
Charlie Sharpsteen
Undergraduate-- Environmental Resources Engineering
Humboldt State University
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