b <- c(0,1,0,1,1,1,0,0,1,1,0,0,0,0,1,1,1,1,1,1,1,1,1,0,1,0,0,1,1,1,0,1,0,1,0,1,0,0,
       0,0,0,0,0,0,1,0,1,1,0,0,1,1,1,0,1,0,1,0,0,0,1,0,0,1,0,1,0,1,0,0,0,0,0,0,0,0)

N=length(b);k=1;
for (i in 1:N-1) {
  if(b[i] !=b[i+1]){k=k+1;r=k}
}
为什么会报下面的错误？新手不知道为什么会这样，望各位大神求解
Error in if (b[i] != b[i + 1]) { : argument is of length zero