[R] Quick partitioning

[Prof Brian Ripley]

On Thu, 25 Aug 2005, Anna Oganyan wrote:

> Hello,
> I am quite new in R, and  I have one problem:
> I have large d-dimensional data sets (d=2, 3, 6, 10). I would like to
> divide the d-dim space into n (n may be 10, but better some larger
> number, for example 20) equally sized d-dim hypercubes  and count  how
> many data points are in each cube. Is there any way to do  it quickly, I
> mean - in a reasonable time? Actually, I  want  to get some rough idea
> of underlying densities of these data and compare them.
> Thanks a lot!
> Anna

How do you divide a 10D space into 10 hypercubes?  You need at least 
some of dimensions to be undivided.

The general idea is easy: apply cut() to each dimension, so your 
dimensions become factors, then table() will produce the counts.  That 
will be quick enough for millions of points.

-- 
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