How to rewrite code for vector creation in common case?

Question

I need to create the vector cx=(1, 1, 1, 2, 2, 2, 3, 3, 3). I have wrote a code.

k <- 3
tmp <- matrix(0, k, k)
tmp[1,] <-rep(c(1), times = k)
tmp[2,] <-rep(c(2), times = k)
tmp[3,] <-rep(c(3), times = k)

cx <-c(t(tmp))
cx
#[1] 1 1 1 2 2 2 3 3 3

Result is right for me but the code is very long. How to rewrite code for arbitrary number k? My variant is:

k <- 3
tmp <- matrix(0, k, k)
for(i in 1:k) tmp[i,] <-rep(c(i), times = k)
cx <-c(t(tmp))

Use the `each` argument of `rep`: `rep(1:3, each = 3)`. – Feb 01 '16 at 02:23 — , Feb 01 '16 at 02:23

score 3 · Accepted Answer · answered Feb 01 '16 at 02:25

3

rep function is good enough, but the Kronecker product is worth mentioning.

kronecker(1:3, rep(1, 3))

answered Feb 01 '16 at 02:25

Kota Mori

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Right :p Just to socialize kronecker function... – Kota Mori Feb 01 '16 at 02:32

How to rewrite code for vector creation in common case?

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