generating a sequence

Tue, Dec 21, 1999 7:23 AM

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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generating a sequence

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