Re: [R] Creating a large matrix

From: Vehbi Sinan Tunalioglu <>
Date: Mon 06 Jun 2005 - 01:15:48 EST

Hash: SHA1

You are able to store such a huge matrix in R, if you ask for it... Furthermore, "table" command might help you:

Help page for "table" says:

Cross Tabulation and Table Creation

     'table' uses the cross-classifying factors to build a contingency
     table of the counts at each combination of factor levels.

Take a look at the examples on the Help page.

Des Callaghan wrote:
> Dear all,
> I have a set of data that is 2 columns wide and 35,000 rows long (see
> extract below). The first column contains codes for tetrads (2km x 2km
> squares within NW England) and the second column has the names of moss
> species present within each tetrad. I wish to convert this into a matrix
> where rows are labelled by 'Tetrad', columns are labelled by 'Moss species'
> and each cell contains a 1 or 0 to denote the presence or absence of the
> moss species within each tetrad. This would be a matrix measuring 796 rows
> by 417 columns. Am I able to do this within R? I ran into problems trying
> to do it using the crosstab query in MS Access and the pivot table function
> on MS Excel because there are too many columns for these software to handle.
> Thanks very much in advance for any help.
> All the best,
> Des
> Tetrad Moss species
> SD20S Amblystegium serpens var. serpens
> SD20S Barbula convoluta
> SD21S Brachythecium albicans
> SD20J Brachythecium rutabulum
> SD30S Bryum argenteum
> SD20S Bryum capillare
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