How to repeat a procedure

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