Unbalanced nesting S+ code for design variables

["Shakir Hussain" <hussains@medmail2.bham.ac.uk>]

Dear friends,
For the following unbalanced design:

  L3  L2 L1
1  1   1  1
2  1   1  2
3  1   1  3 
4  1   2  1
5  1   2  2
6  1   3  1
7  1   4  1
8  1   4  2
9  1   4  3
10 2   1  1
11 2   1  2
12 2   2  1
13 2   2  2
14 2   2  3
15 2   3  1

I use,
list( 
L3=c(1,1,1,...,2,2,2),L2=c(1,1,1,2,2,3,...,2,2,2,3),L1=c(1,2,3,1,2,...,1,2,3,1)).

Wonder how can I generate unbalance-nesting structure for (L3, L2, L1) by using 
S+ code?

Thanks in advance.
Shakir