Message-ID: <14431.42863.62537.411008@gargle.gargle.HOWL>
Date: 1999-12-21T16:14:39Z
From: Martin Maechler
Subject: generating a sequence --- need fast [lt]apply ()
In-Reply-To: <199912211523.PAA14129@toucan.stats.ox.ac.uk>
>>>>> 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> Me:
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> rA[rA>=1]
BDR> Andy Royle:
BDR> sequence((n-1):1)
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 [34].y, but not 5.[12])...
Anyone working on this ?
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