[R] Randomising matrices

Gabor Grothendieck ggrothendieck at gmail.com
Fri Apr 27 15:12:58 CEST 2007



On 4/27/07, Nick Cutler <s0455078 at sms.ed.ac.uk> wrote:
> I would like to be able to randomise presence-absence (i.e. binary)
> matrices whilst keeping both the row and column totals constant. Is
> there a function in R that would allow me to do this?
> I'm working with vegetation presence-absence matrices based on field
> observations. The matrices are formatted to have sites as rows and
> species as columns. The presence of a species on a site is indicated
> with a 1 (absence is obviously indicated with a 0).
> I would like to randomise the matrices many times in order to construct
> null models. However, I cannot identify a function in R to do this, and
> the programming looks tricky for someone of my limited skills.
> Can anybody help me out?
> Many thanks,
> Nick Cutler
> Institute of Geography
> School of Geosciences
> University of Edinburgh
> Drummond Street
> Edinburgh EH8 9XP
> United Kingdom
> Tel: 0131 650 2532
> Web: http://www.geos.ed.ac.uk/homes/s0455078
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