On Dec 28, 2009, at 7:03 PM, Seth W Bigelow wrote:
I have a data set similar to this:
P1id Veg1 Veg2 AreaPoly2 P2ID
1 p p 1 1
1 p p 1.5 2
2 p p 2 3
2 p h 3.5 4
For each group of "Poly1id" records, I wish to output (subset) the
record
which has largest "AreaPoly2" value, but only if Veg1=Veg2. For this
example, the desired dataset would be
P1id Veg1 Veg2 AreaPoly2 P2ID
1 p p 1.5 2
2 p p 2 3
Can you be more expansive (or perhaps more accurate?) about the
conditions you want satisfied? Looking at the that dataset, I only see
one row that has the largest value for AreaPoly2 within the three
records where Veg1==Veg2.
Otherwise I would think the answer might be along these lines:
> dft <- read.table(textConnection("P1id Veg1 Veg2
AreaPoly2 P2ID
+ 1 p p 1 1
+ 1 p p 1.5 2
+ 2 p p 2 3
+ 2 p h 3.5 4"), header=T)
> dft$Veg1 <- factor(dft$Veg1, levels=levels(dft$Veg2))
> s.dft <- subset(dft, Veg1==Veg2)
> s.dft[which.max(s.dft$AreaPoly2),]
P1id Veg1 Veg2 AreaPoly2 P2ID
3 2 p p 2 3
--
David
Can anyone point me in the right direction on this?
Dr. Seth W. Bigelow
Biologist, USDA-FS Pacific Southwest Research Station
1731 Research Park Drive, Davis California
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