[R] Loops and memory

[R A F]

Hi, this question is meant to be a bit vague, since I'm really not
familiar with all the issues involved.  It's also a problem that I
think many would have encountered and would have useful suggestions.

According to MASS, 2nd ed., p. 158, "A major issue is that S is
designed to be able to back out from uncompleted calculations, so
that memory used in intermediate calculations is retained until
they are committed."  The end of the paragraph says that recent
versions of S are better.  And I seem to remember that R is also
better with memory management.

My question I guess is how bad loops are in R and what the best
way is to deal with memory if I want to use loops.  Are there flags
I can turn on or off if I don't care about uncompleted calculations
to make memory management more efficient, etc.?  I've already thought
about pushing looping into shell scripts and hope that this will
help somewhat.

The issue I'm facing is that it'd be easier for me to write a program
using a loop, but the loop itself would be a large one (looping over
potentially millions of entries say, with fairly nontrivial
calculations per loop).  Right now I've tried to avoid this through
some pre-processing followed by a more complex set of calculations
than I would have needed to do had I used a loop.  Of course it's
hard to know which method is better without actually trying both,
but I would like to hear your comments on loops in R before deciding
whether I should give the loop approach a try.

Thanks.