[R] matrix form

[Hathaikan Chootrakool]

I am a new user, i was wondering how to define a collection of data in
matrix form,
this is a part of my data,there are 26 studies, 3 Treatments

   Arm No  Study no.  Treatment  Num(r) Total(n)
1    1        1         1          2    43
2    2        1         2          9    42
3    3        1         3          13   41
4    4        2         1          12   68
5    5        2         2          13   73
6    6        2         3          13   72
7    7        3         1           4   20
8    8        3         3           4   16
9    9        4         1          20   116
10  10        4         3          30   111

I would like to use matrix [study No,Treatment] how can i define code for
using matrix?

has anyone can help me?,thank you very much.

Hathaikan