[R] summary table newbie question

[Jeff D. Hamann]

I've got a newbie question and I got a little lost in the "table helps".
I've got a data.frame I would like to summarize as a (and pardon for the
lack of correct vernacular) data collection matrix. My data looks like,

   stand siteindex age      acres  pct.acres
1    232       116  45  8477.3105 0.56159458
2    234       121  25 11120.1530 0.73667441
3    235       132  25  5399.4605 0.35769691
4    236       115   5  6308.3969 0.41791103
5    240       116  45   473.1533 0.03134489
6    241       116  15 21790.9595 1.44358105
7    245       171  25   686.9867 0.04551066
8    246       134  25 15176.8082 1.00541478
9    247        99  35  1754.9282 0.11625835
10   251       125  55  7396.1098 0.48996851
...blah, blah, blah...


and when I attempt to create a summary table using aggregate, I get the
following results,

> aggregate( stands$acres, by=list(stands$age,stands$siteindex), sum )

    Group.1 Group.2          x
1        95      86  6403.5457
2         5      88  1517.6781
3        45      88  3555.3213
4       125      89  6269.2633
5        95      90  3154.3531
6        55      93 14006.9781
7        15      94    98.9918
8        35      94  2241.0531
9       105      94   431.0281

but what I really want is a matrix where the rows and columns are classes
(in increments of 5 or 10 or whatever) and the cells are the sums (or means
or whatever) for the data.frame. I guess it would be equivalent to like
surf.ls/surf.gls without fitting a trend but that would also allow me to
plot the results graphically in addition to simply printing out the table
using xtable.

Jeff.

---
Jeff D. Hamann
Forest Informatics, Inc.
PO Box 1421
Corvallis, Oregon USA 97339-1421
541-754-1428
jeff.hamann at forestinformatics.com
www.forestinformatics.com