[Rd] Dropping dimnames doesn't matter (anymore)?
Prof Brian Ripley
ripley at stats.ox.ac.uk
Fri May 12 15:16:00 CEST 2006
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, 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
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