[R] sub data frame by expression

[Arne.Muller@aventis.com]

Hi All,

I've the following data frame with 54 rows and 4 colums:

> x                  
                  Ratio  Dose Time Batch
R.010mM.04h.NEW    0.02 010mM  04h   NEW
R.010mM.04h.NEW.1  0.07 010mM  04h   NEW
...
R.010mM.24h.NEW.2  0.06 010mM  24h   NEW
R.010mM.04h.OLD    0.19 010mM  04h   OLD
...
R.010mM.04h.OLD.1  0.49 010mM  04h   OLD
R.100mM.24h.OLD    0.40 100mM  24h   OLD

I'd like to create a sub data frame containing all rows where Batch == "OLD"
and keeping the 4 colums. Assume that I don't know the order of the rows
(otherwise I could just do something like x[1:20,]).

I've tried x[x$Batch == 'OLD'] or x[x[,4] == 'OLD'] but it generates errors.
So I assume I've still not realy understood the philosophy of indexing ...
:-(

What's the easiest way to do this, any suggestions?

	thanks a lot for you help,

	Arne