History of seq and seq.int
The history is open for all to see. E.g. from the NEWS file (ONEWS in
pre-2.12.0) entry for R 2.4.0
o There is a new primitive seq.int() which is slightly more
restricted than seq() but often very much faster, and new
primitives seq_along() and seq_len() which are faster still.
It isn't just complex values: seq.default() dispatches on methods for
e.g. arithmetic so is potentially quite a lot more general. And if
you look back, seq() was in R 'for ever' as an interpreted generic
function -- its peculiarities are taken from blue-book S (although not
necessarily documented there).
We provide faster versions for use where needed -- but it is rather
rare that seq() takes up more than a tiny proportion of the run time
of an R task (and we do provide tools to find out). Those faster
versions are used in R's own code where suitable (and as I discovered
recently, in a couple of places where not).
On Wed, 29 Sep 2010, Radford Neal wrote:
I wonder what is the history of "seq" and "seq.int"?
From "help(seq)", one reads that "'seq.int' is an internal generic
which can be much faster but has a few restrictions". And indeed, "seq.int(1,99,by=2)" is over 40 times faster than "seq(1,99,by=2)" in a quick test I just did. This is not surprising given that "seq" is written in R whereas "seq.int" is a primitive written in C. The only documented restriction on "seq.int" that I can see is that it won't produce complex-valued sequences. It would be nice if the 40-times-faster version could replace the slow version, if it can be made to do the same thing. But is there some reason I don't see that this makes this hard? Was the C version the original, and then someone decided that complex number support was essential, and most easily obtained by translating it to R? (The R code and C code are very parallel, so there was certainly a translation rather a rewrite one way or the other.) Or was the original in R, and someone rewrote it in C for speed, but stopped just short of being able to replace the R version with the C version because they didn't implement complex-valued sequences? Or is there some other feature that's missing from seq.int?
Brian D. Ripley, ripley at stats.ox.ac.uk Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG, UK Fax: +44 1865 272595