[R] Transferring data from S+ to R

[Simon Fear]

In rw0631 I find that even the unsubscripted version does not hugely
increase workspace requirements - i.e. R *does* instantly clear out the
useless copies and make looping memory-feasible.

Apologies. I don't know if it's becuase I'm running a later version now,
or whether I made some stupid mistake last time I tried it.

Simon Fear


-----Original Message-----
From: Douglas Bates [mailto:bates at stat.wisc.edu]
Sent: 15 January 1999 14:56
To: Simon Fear
Cc: r-help at stat.math.ethz.ch; 'Jim Lindsey'
Subject: Re: [R] Transferring data from S+ to R


>>>>> "Simon" == Simon Fear <fears at roycastle.liv.ac.uk> writes:

  Simon> Not that I have got it quite right yet though; I still
  Simon> haven't worked out how to make, for example,

  Simon> var1 <- rnorm(10000)

  Simon> not create a new instance, eating 10000 globs of memory,
  Simon> every time it is called within a loop;

I think if you make the construction look like

 var1 <- double(10000)
 for (i in 1:niter) {
   var1[] <- rnorm(10000)  # replacement rather than assignment
   ...
 }

you avoid the multiple copies.  I haven't tested this particular case
but the basic idea is that replacement of elements of a vector is done
in-place, if possible, and not be creating a new object.  Assignment
to a name will usually result in a new object being created in a way
that masks the previous objects with that name. 
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