Dropping dimnames doesn't matter (anymore)?

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Dropping dimnames doesn't matter (anymore)?

Bjørn-Helge Mevik
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?

--
Bjørn-Helge Mevik

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Re: Dropping dimnames doesn't matter (anymore)?

Prof Brian Ripley
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,                  [hidden email]
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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