[R] (Most efficient) way to make random sequences of random sequences

[Emmanuel Levy]

Hi,

I was wondering the what would be the (most efficient) way to generate
a sequence
of sequences, i mean:

if I have 1,2 and 3.

I'd like to generate a sequence of length N*3 (N ~ 1,000,000 or more)

Where random permutations of the sequence 1,2,3 follow each other.

i.e  1,2,3,1,3,2,3,2,1

/!\ The thing is that there should never be twice the same number of
in the same sub-sequence, meaning that this is different from
generating a vector with the numbers 1,2 and 3 randomly distributed.

Any suggestion very welcome! Thanks,

Emmanuel