[R] random section of samples based on group membership

[Wade Wall]

Hi all,

I have a matrix of 474 rows (samples) with 565 columns (variables).
each of the 474 samples belong to one of 120 groups, with the
groupings as a column in the above matrix. For example, the group
column would be:

1
1
1
2
2
2
.
.
.
120
120

I  want to randomly select one from each group.  Not all the groups
have the same number of samples, some have 4, some 3 etc.  Is there a
function to do this, or would I need to write a looping statement to
look at each successive group?

I basically want to combine the randomly selected samples from the 120
groups into a new matrix in order to perform a cluster analysis.

Thanks,
Wade