Re: [R] generating a sequence

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Prof Brian Ripley (ripley@stats.ox.ac.uk)
Tue, 21 Dec 1999 15:23:49 +0000 (GMT) 




OK, so we have now seen essentially three solutions:



Me:



A <- matrix(1, n-1, n-1)


rA <- row(A)


rA[rA + col(A) <= n]



Jonathan Rougier:



rA <- outer(1:n, 1:n, "-")


rA[rA>=1]



Andy Royle:



sequence((n-1):1)



Timings for n=500 on a 1994 Sun Sparc 20:



3.29, 4.68 and 23.86 seconds.



I deliberately did not use outer, as it calls apply and 


is normally quite slow.  row and col are internal operations and fast.



-- 
Brian D. Ripley,                  ripley@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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