From: Paul Chatfield <paulosdoulos_at_yahoo.co.uk>

Date: Thu 18 May 2006 - 18:12:45 EST

Jacques VESLOT

R-help@stat.math.ethz.ch mailing list

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Thu May 18 18:16:59 2006

Date: Thu 18 May 2006 - 18:12:45 EST

x<-1:4

trial<- function(x)

{xx<-matrix(runif(20), 2, 10)

if (xx[1,x]<0.5) { ...}

Jacques VESLOT <jacques.veslot@good.ibl.fr> wrote: ?cumsum

> system.time({ z <- NULL ; for (i in 1:1000) z <- c(z, sum((1:i)**2)) })

[1] 0.04 0.00 0.04 NA NA

> system.time( zz <- cumsum((1:1000)**2) )

[1] 0 0 0 NA NA

> all.equal(z,zz)

**[1] TRUE
**

Jacques VESLOT

**CNRS UMR 8090
**

I.B.L (2ème étage)

1 rue du Professeur Calmette

B.P. 245

59019 Lille Cedex

Tel : 33 (0)3.20.87.10.44

Fax : 33 (0)3.20.87.10.31

Paul Chatfield a écrit :

> Hi - I'm trying to avoid using a 'for' loop due to inefficiency and instead use a function (and ultimately tapply as I'm working on a matrix) but I can't figure out how to get 'function' to take the variables as anything other than vectors for example

*>
**> aa<-0
**> x<-1:4
**> test.fun<-function(x)
**> {aa<-(x*x +aa)
**> return(aa)}
**> test.fun(1:4)
**>
**> This code returns 'aa' as 1 4 9 16, but I'd like it to return aa as 1 5 14 30 taking into consideration that I've just calculated aa for x=1. Aside from using loops, is there not a simple way of telling R to work out x for consecutive values?
**>
**> thanks
**>
**> Paul Chatfield
**>
**>
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