[R] generating a sequence

[Prof Brian Ripley]

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 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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