try this: > x <- 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=TRUE, as.is=TRUE) > # split the dataframe by P1id > x.s <- split(x, x$P1id) > # now go through the sets to see which is the largest > result <- lapply(x.s, function(.sub){ + .match <- subset(.sub, Veg1 == Veg2) + if (length(.match) > 0){ + return(.match[which.max(.match$AreaPoly2),]) + } + else { + return(NULL) + } + }) > do.call(rbind, result) P1id Veg1 Veg2 AreaPoly2 P2ID 1 1 p p 1.5 2 2 2 p p 2.0 3 >
On Mon, Dec 28, 2009 at 8:03 PM, Seth W Bigelow <sbige...@fs.fed.us> 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 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 > [[alternative HTML version deleted]] > > ______________________________________________ > R-help@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide > http://www.R-project.org/posting-guide.html<http://www.r-project.org/posting-guide.html> > and provide commented, minimal, self-contained, reproducible code. > -- Jim Holtman Cincinnati, OH +1 513 646 9390 What is the problem that you are trying to solve? [[alternative HTML version deleted]] ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.