Insert elements into a vector in a defined positions

Dear R users,
I have a vector of length n and I want to insert some elements (in  
my case
the NA string) into a defined positions. For example, my vector is  
z1 and I
want to add NA's in positions 4, 6 y 7 so after that, my new  
vector, z2,
should have a length of 10+3.

  z1 <- 1:10
  id <- c(4,6,7)

  # And z2 should be:
  z2 <- c(1,2,3,NA,4,5,NA,NA,6,7,8,9,10)

Anyone knows how can I do that?

At first I thought append() might work ... but the "after"
argument to append seems to have to be of length 1.

How about:

	z2 <- numeric(length(z1)+length(id))
	z2[id] <- NA
	z2[!is.na(z2)] <- z1

A bit kludgy, but it appears to work.

	cheers,

		Rolf Turner

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