[R] Subsetting with more than one criteria

[CG Pettersson]

Hello all!

I have been using R for two years, but still have trivial problems.
For the moment, I run R1.9.1 on a W2k computer.

I work with a dataset from a variety evaluation project. Every year 25
varieties have been tested. The tested cultivars have been the same
each year in all trials, but some have changed over the three year
period. Now I want to do some calculations and plotting on subsets.
The structure looks like this:

Year	ADB	Block	Vcode	Variety	Yield	Protein			
2002	SW0024	1	20226	Denise	5843	12.8....	
2002	SW0024	1	9865	Astoria	6729	11.4	
2002	SW0024	1	9622	Barke	6121	12	
2002	SW0024	1	9604	Cecilia	5579	12.7	
2002	SW0024	1	20223	Granta	5591	11.6	
2002	SW0024	1	20222	Class	5591	11.7	
2002	SW0024	1	9922	Wiking	5744	12.5
2002	SW0024	1	20103	Vortex	5863	10.6
.
.
And so on both down and sideways.
Three years and four trials with three replicats each gives 900 lines.


How do I use several criteria to subset this?

Ast <- subset(data, Variety == "Astoria") 

works fine giving back the 36 lines where Astoria appears.
But how do I pick two (or more) varieties? AND picking one (or two)
years?

Everything I have tried results in rubbish, like:

AstBark <- subset(data, Variety == c("Astoria","Barke"))

which seems to work but gives back 19 and 18 lines of the varieties 

respectively. There exists 36 of each....

Thanks

/CG


CG Pettersson, MSci, PhD Stud.
Swedish University of Agricultural Sciences
Dep. of Ecology and Crop Production. Box 7043
SE-750 07 Uppsala