On Fri, 12 May 2006, Bjørn-Helge Mevik wrote:
In the "old days", one way of speeding up matrix calculations was to drop the dimnames of the matrices prior to the calculations, i.e., dimnames(X) <- NULL. I distinctly remember that this could have a great impact at least in Splus 3.x (under UNIX/Linux).I just did a small, informal test of this with a couple of functions I use to fit plsr models, in R 2.3.0 (Linux). It didn't seem to have any effect at all (the functions actually ran a tiny bit slower, probably due to the "dimnames(X) <- NULL" command). Is the "general rule-of-thumb" with current R versions that the overhead of keeping the dimnames through calculations is negligible?
It depends on whether the dimnames are an appreciable part of the size of the object. If they are (e.g. a nx1 array for large n) then manipulating them will add an appeciable overhead. (BTW, character vectors such as dimnames are faster in R for some operations but take much more memory.)
-- Brian D. Ripley, [EMAIL PROTECTED] 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
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