It’s not always the case that loops are slow and apply is fast. There’s a nice discussion of this in the May, 2008, issue of R News:
Uwe Ligges and John Fox. R Help Desk: How can I avoid this loop or
make it faster? R News, 8(1):46-50, May 2008.
In the section “Loops!” (starting on pg 48), they say:
Many comments about R state that using loops is a particularly bad idea. This is not necessarily true. In certain cases, it is difficult to write vectorized code, or vectorized code may consume a huge amount of memory.
They further suggest:
- Initialize new objects to full length before the loop, rather
than increasing their size within the loop.- Do not do things in a
loop that can be done outside the loop.- Do not avoid loops simply
for the sake of avoiding loops.
They have a simple example where a for loop takes 1.3 sec but apply runs out of memory.