[R] dist

Prof Brian Ripley ripley at stats.ox.ac.uk
Mon Nov 19 15:08:58 CET 2001

On Mon, 19 Nov 2001, Agustin Lobo wrote:

> Hi list!
> I'm computing multivar. distances from a set of centroids
> to a (large) set of individuals. I'm now just using rbind
> to create a matrix (x) with the centroid and the individuals,
> then run as.matrix(dist(x)) and finally select the appropriate columns,
> as I'm not interested on the distances among individuals.
> Therefore, this procedure implies a waste of computing time.
> Is there any way to use dist only between each individual
> and the centroids (avoiding loops in R)? or should I just go and try to
> make
> a modified version of dist by hacking the C code?

You don't need C code for this.  Take a look at e.g. predict.lda and
predict.qda.  You might want to do the individuals in batches if the
number really is large (millions?).

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 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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