How to repeat a procedure

Thanks, Patrick. I was aware of that and was able to fix it.

Thanks Tom, Wayne and Peter for all your help.

Heyen



                                                                                                                                       
                      Patrick Burns                                                                                                    
                      <pburns at pburns.se        To:       Thomas Lumley <tlumley at u.washington.edu>                                      
                      anet.com>                cc:       Haiyan Chen <hxc05 at health.state.ny.us>, R-help at stat.math.ethz.ch              
                                               Subject:  Re: [R] How to repeat a procedure                                             
                      02/18/2004 01:09                                                                                                 
                      PM                                                                                                               
                                                                                                                                       
                                                                                                                                       




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

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

should read:

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

or just

x3 <- rpois(50 * 100, mu)

Patrick Burns

Burns Statistics
patrick at burns-stat.com
+44 (0)20 8525 0696
http://www.burns-stat.com
(home of S Poetry and "A Guide for the Unwilling S User")

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<-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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