Be very careful of the idiom
1:length(x)What if x has length 0? Then this is 1:0 and we get two elements. So y[1:length(x)] would yeild y[c(1, 0)] and give the first element.
What about
for(i in 1:length(x)) {
...
}This would give two iterations where i is 1 and then 0.
Instead, we nearly always want
seq(along = x)