[R] index to select rows of a large matrix

[tsunhin wong]

Dear R Users,

I have created a 1500 x 20000 data frame - DataSeq. Each of the 1500
rows represents a data sequence.
I have another data frame iData that stores the information of these
1500 data sequences in the same order, for example, condition, gender,
etc.

If I use "subset" to select certain groups within iData according to
some criteria that I have set, e.g. condition, gender
Then how can I used the retrieved subset of iData to point to and
retrieve corresponding rows in the DataSeq data.frame for
manipulations and analysis?

I hope some of you can give me some idea!
Thank you very much!!!

- John