insert elements in a vector in R

Question

I have a vector in R,

a = c(2,3,4,9,10,2,4,19)

let us say I want to efficiently insert the following vectors, b, and c,

b =         


        

Answer 1

Here's another function, using Ricardo's syntax, Ferdinand's split and @Arun's interleaving trick from another question:

ins2 <- function(a,bs,pos){
    as <- split(a,cumsum(seq(a)%in%(pos+1)))
    idx <- order(c(seq_along(as),seq_along(bs)))
    unlist(c(as,bs)[idx])
}

The advantage is that this should extend to more insertions. However, it may produce weird output when passed invalid arguments, e.g., with any(pos > length(a)) or length(bs)!=length(pos).

You can change the last line to unname(unlist(... if you don't want a's items named.