[R] R matrix sorting question

[insu_paek@harcourt.com]

Dear there,

     I am trying to do the following stuff. Could you let me know how to do
it efficiently?

    > aaa
     [,1] [,2]
[1,]    1 -0.2
[2,]    3  0.8
[3,]    4  0.3
[4,]    5  0.2
[5,]    7  0.9

 And I would like to sort the matrix by column 2 (and accordingly  column 1
sorted as well).
The desired matrix will be

1  -0.2
5   0.2
4   0.3
3   0.8
7   0.9

If using Excel or SAS, I can do this easily, but I couldn't figure out how
to do it in R.
  Could you let me know the efficient way to do this ?
 I appreciate if the solution or reply comes as quickly as possible.

 Thank you very much.

Insu