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