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Efficiency question
2 messages · Worik R, Joris Meys
On Tue, Jun 8, 2010 at 11:53 PM, Worik R <worikr at gmail.com> wrote:
Given the following snippet.... ?m.nf.xts <- xts(rep(0, length(index(m.xts))), order.by=index(m.xts)) Does R know to cache the index(m.xts) or is it more efficient to say... m.i <- index(m.xts) ?m.nf.xts <- xts(rep(0, length(m.i)), order.by=index(m.i))
this is one call less to a function, and hence more efficient. I suppose it has to be order.by=m.i Btw, How should R know what to cache? If it would cache all calculations, you'd be out of memory in no time. If you have more questions like this, you can test it by yourself, eg :
x <- sample(rnorm(100))
id <- index(x) # is in this case equivalent to 1:100
system.time(replicate(10^5,{rep(0,length(index(x)))[index(x)]}))
user system elapsed 7.61 0.09 7.76
system.time(replicate(10^5,{rep(0,length(id))[id]}))
user system elapsed 1.49 0.06 1.58 Cheers Joris
? cheers Worik ? ? ? ?[[alternative HTML version deleted]]
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Joris Meys Statistical consultant Ghent University Faculty of Bioscience Engineering Department of Applied mathematics, biometrics and process control tel : +32 9 264 59 87 Joris.Meys at Ugent.be ------------------------------- Disclaimer : http://helpdesk.ugent.be/e-maildisclaimer.php