[R] generating a sequence --- need fast [lt]apply ()
maechler at stat.math.ethz.ch
Tue Dec 21 17:14:39 CET 1999
>>>>> On Tue, 21 Dec 1999 15:23:49 +0000 (GMT), Prof Brian Ripley <ripley at stats.ox.ac.uk> said:
BDR> OK, so we have now seen essentially three solutions:
BDR> A <- matrix(1, n-1, n-1)
BDR> rA <- row(A)
BDR> rA[rA + col(A) <= n]
BDR> Jonathan Rougier:
BDR> rA <- outer(1:n, 1:n, "-")
BDR> Andy Royle:
BDR> Timings for n=500 on a 1994 Sun Sparc 20:
BDR> 3.29, 4.68 and 23.86 seconds.
BDR> I deliberately did not use outer, as it calls apply and
BDR> is normally quite slow. row and col are internal operations and fast.
Thanks a lot.
I hope this reminds more people than just me
that we (R users) "desperately" need someone who
rewrites apply(),lapply(), and tapply()
to become much faster (as they are with S-plus .y, but not 5.)...
Anyone working on this ?
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