Re: [R] controling the size of vectors in a matrix 1) Your colnames need 4 elements and not 3 2) Utilize the argument 'n' in your random number generators Your codes could be simplified as:   m <- cbind( treatmentgrp  = sample( 1:2, n, replace=T ),               strata        = sample( 1:2, n, replace=T ),               survivalTime  = rexp( n, rate=0.07 ),               somethingElse = rexp( n, rate=0.02 ) ) Regards, Adai raymond chiruka wrote: > hie R users >     >   l have the following matrix >       n=20 >       m<-matrix(nrow=n,ncol=4) >       colnames(m)=c("treatmentgrp","strata","survivalTime")                   >           for(i in 1:n) m[i,]<-c(sample(c(1,2),1,replace=TRUE),sample(c(1:2),1,replace=TRUE),rexp(1,0.07),rexp(1,0.02))                                                                   >     >       print(m) >     1.l would like to control the size of the treatment variable eg treatment 1=size 5 treatment 2=size 15. >    >   2. l would also want to control the size of the strata ie in treatment 1 divide the strata in to 2 etc. >    >   3. For the survival time l would like to have treatment 1-strata 1  using a different rate  from treatment 2 -strata 2 etc to generate  the survival time. >    >   the program l used above does nt do this so if you can help >    >   thanks  >    >         > --------------------------------- > Building a website is a piece of cake.  >  > 	[[alternative HTML version deleted]] >  > ______________________________________________ > R-help@stat.math.ethz.ch mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. >  >  > ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.