[R] passing the reference in R functions
tlumley at u.washington.edu
Fri Mar 8 18:19:43 CET 2002
On Fri, 8 Mar 2002, Rangrej, Jagadish wrote:
> is it possible to send the vector in the r functions without making the
> function frame to actually have the replicate copy of it ?
If you're asking what I think you're asking, then yes.
R appears to pass arguments by value, so when you do
the effect is as if the mean() function received a copy of verybigarray.
However, R doesn't *actually* copy arguments until they are modified, so
the copy is really just a reference to the original array and takes up
very little memory.
You can see the difference by creating a large vector, say,
gcinfo(TRUE) #report when memory is garbage collected
system.time(mean(x)) #mean() does copy and modify its argument
system.time(sum(x)/1e6) #sum() doesn't
You will see that mean() is slower and causes garbage collection.
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