The command ?apply will easily get row means/vars (or col means/vars)

e.g.  
my.mat<-matrix(rnorm(144),12)
my.mat
apply(my.mat,1,mean,na.rm=T)
apply(my.mat,1,var,na.rm=T)



The functions ?rbind and ?cbind will help you add rows or columns to
matrices or data frames

Enjoy 

Wayne


-----Original Message-----
From: Haiyan Chen [mailto:hxc05@health.state.ny.us]
Sent: 18 February 2004 15:39
To: R-help@stat.math.ethz.ch
Subject: [R] How to repeat a procedure


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},

2. I want to calculate means and sample variances of each row and create a
new matrix 100x2;

3. I then want to repeat above procedure 500 times so that eventually I
will have 500 100x2 matrices.

Would someone mind helping me to code 2 & 3?

Thanks ahead of time.

Heyen

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