# [R] How to repeat a procedure

Patrick Burns pburns at pburns.seanet.com
Wed Feb 18 19:09:16 CET 2004

```I believe that Thomas got "mu" wrong.  If I understand
correctly, the line:

x3 <- rpois(50 * 100, rep(mu, each=100))

x3 <- rpois(50 * 100, rep(mu, 50))

or just

x3 <- rpois(50 * 100, mu)

Patrick Burns

Burns Statistics
patrick at burns-stat.com
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Thomas Lumley wrote:

>On Wed, 18 Feb 2004, Haiyan Chen wrote:
>
>
>
>>Hello,
>>
>>1. After I generate a 100x50 matrix by x3<-matrix(0,100,50);for (i in
>>1:100) {x1<-rpois(50, mu[i]);x2<-x1; x2[runif(50)<.01]<-0; x3[i,]<-x2},
>>
>>
>
>YOu can do this without the loop, eg
>
>x3<-rpois(50*100, rep(mu,each=100))
>x3<-ifelse(runif(50*100)<0.01, 0, x3)
>x3<-matrix(x3, ncol=50)
>
>
>
>>2. I want to calculate means and sample variances of each row and create a
>>new matrix 100x2;
>>
>>
>
>means<-apply(x3,2,mean)
>vars<-apply(x3,2,var)
>cbind(means,vars)
>
>
>
>>3. I then want to repeat above procedure 500 times so that eventually I
>>will have 500 100x2 matrices.
>>
>>
>
>make.a.matrix<-function(...){
>	x3<-rpois(50*100, rep(mu,each=100))
>	x3<-ifelse(runif(50*100)<0.01, 0, x3)
>	x3<-matrix(x3, ncol=50)
>	cbind(apply(x3,2,mean), apply(x3,2, var))
>}
>
>many.matrices<-lapply(1:500, make.a.matrix)
>
>gives a list of 500 matrices.  This isn't quite the most efficient
>solution, but it's not bad.
>
>
>	-thomas
>
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>
>
>

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