Group by in R

Gabor Grothendieck wrote:

SQL has the order by clause.

Gabor, thanks for the suggestion. I thought about this but ORDER BY cannot
create the tabular structure that I need. Here is more detail about my
setting:

f1, f2, f3 have unique triplets (each repeating a different number of
times). Each of these triplets falls into one of the two categories of f4.
Here is a sample:

data

? X1 X2 X3 X4
1 ? 1 ?2 ?2 ?1
2 ? 1 ?1 ?2 ?2
3 ? 1 ?1 ?2 ?2
4 ? 2 ?2 ?1 ?2
5 ? 1 ?1 ?2 ?2
6 ? 2 ?2 ?1 ?2
7 ? 1 ?1 ?2 ?1
8 ? 2 ?2 ?1 ?2
9 ? 1 ?2 ?1 ?1
10 ?1 ?1 ?2 ?2

sqldf("select X1, X2, X3, X4, count(*) CNT from data group by X1, X2, X3, X4
ORDER BY X4, X1, X2, X3")

?X1 X2 X3 X4 CNT
1 ?1 ?1 ?2 ?1 ? 1
2 ?1 ?2 ?1 ?1 ? 1
3 ?1 ?2 ?2 ?1 ? 1
4 ?1 ?1 ?2 ?2 ? 4
5 ?2 ?2 ?1 ?2 ? 3

The counts are fine, though it's not exactly what I need. I need a kind of
contingency table:

? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? | levels of X4 |
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ---------------
unique triplets of X1:X3 | ?1 ? | ? 2 ? |

-----------------------------------------
? ? ? ? ? ?1 1 1 ? ? ? ? ? ? | ?0 ? ? ? 0
? ? ? ? ? ?1 1 2 ? ? ? ? ? ? | ?1 ? ? ? 4
? ? ? ? ? ?1 2 1 ? ? ? ? ? ? | ?1 ? ? ? 0
? ? ? ? ? ?1 2 2 ? ? ? ? ? ? | ?1 ? ? ? 0
? ? ? ? ? ?2 1 1 ? ? ? ? ? ? | ?0 ? ? ? 0
? ? ? ? ? ?2 1 2 ? ? ? ? ? ? | ?0 ? ? ? 0
? ? ? ? ? ?2 2 1 ? ? ? ? ? ? | ?0 ? ? ? 3
? ? ? ? ? ?2 2 2 ? ? ? ? ? ? | ?0 ? ? ? 0


So the final result should be a table structure like:


0 0
1 4
1 0
1 0
0 0
0 0
0 3
0 0

I guess I could probably do this in SQL with a combination of OUTER JOINs
but I thought
that R might have a more elegant solution based on "factor" and "table".

Thanks,
Nick
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