[R] simulate binary markov chain

[Chris Oldmeadow]

Hi all, I was hoping somebody may know of a function for simulating a 
large binary sequence (length >10 million) using a (1st order) markov 
model with known (2x2) transition matrix. It needs to be reasonably 
fast. I have tried the following;

mc<-function(sq,P){
  s<-c()
  x<-row.names(P)
  n<-length(sq)
  p1<-sum(sq)/n
  s[1] <- rbinom(1,1,p1);
  for ( i in 2:n){
     s[i] <- rbinom( 1, 1, P[s[i-1]+1] )
  }
  return(s)
}


P<-c(0.63,0.27)
x<-rbinom(500,1,0.5)
new<-mc(x,P)

thanks in advance!
Chris