[R] Tabulation of aggregated data.frame

[Oh Dong-hyun]

Hi useRs!

I would like to know how to make aggregated data.frame with  
aggregate() tabulated.

For example, I run the following command to aggregate re with respect  
to group1 and group2.

 > (aggr <- with(final, aggregate(re, group1, group2, mean)))
     Group.1 Group.2       x
1      1992      15 0.16392
2      1993      15 0.15467
3      1994      15 0.15456
4      1995      15 0.15391
5      1996      15 0.16511
6      1997      15 0.17368
7      1998      15 0.17955
8      1999      15 0.19805
9      2000      15 0.20546
10     1992      16 0.16237
11     1993      16 0.18359
12     1994      16 0.13811
13     1995      16 0.13988
14     1996      16 0.15604
15     1997      16 0.16802
16     1998      16 0.16978
17     1999      16 0.18407
18     2000      16 0.18646
19     1992      17 0.24604
20     1993      17 0.25263
21     1994      17 0.21407
22     1995      17 0.26483
23     1996      17 0.26427
24     1997      17 0.26282
25     1998      17 0.31137
26     1999      17 0.26982
27     2000      17 0.22898
28     1992      18 0.29417
29     1993      18 0.36586
30     1994      18 0.25143
31     1995      18 0.25570
32     1996      18 0.24628
33     1997      18 0.24293
34     1998      18 0.24888
35     1999      18 0.19515
36     2000      18 0.18057

I want make aggr as follows with class of data.frame.
        1992          1993          1994   1995   1996   1997   1998    
1999   2000
15   0.16392    0.15467......
16   0.16237    0.18359.......
17   .....
18   ......

Thank you in advance.