[R] sparse matrix

[Prof Brian Ripley]

On Mon, 8 Jan 2001, Martin Gotz wrote:

> Hi R users,
> 
> I have problem with very large matrix - sparse matrix. Is in R any
> possibility how effective use matrix with a lots of the same number (0 or
> some X)?    
> 
> I think every element of matrix in R now needs own memory space.

A matrix in R is a vector plus a dim atttribute.  I presume you mean a
numeric matrix (there are other types).  Then it needs a 8byte space per
entry.

There are other ways to handle matrices: look at package Matrix, for
example.

One obvious representation is to store the non-zero elements and their
locations.

Just how large is this matrix, and does it have a pattern to its sparsity?
And what do you want to do with it?  Doing things with sparse matrices has
a tendency to make them less sparse.

-- 
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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