On Fri, Mar 18, 2011 at 10:48:44AM -0700, Nicolas Gutierrez wrote: > Hello, > > One more question.. I have the data.frame "pop": > > xloc yloc gonad ind Ene W Area > 1 23 20 516.74 1 0.02 20.21 1 > 2 23 20 1143.20 1 0.02 20.21 1 > 3 23 20 250.00 1 0.02 20.21 1 > 4 22 15 251.98 1 0.02 18.69 2 > 5 22 15 598.08 1 0.02 18.69 2 > 6 21 19 250.00 1 0.02 20.21 3 > 7 22 20 251.98 1 0.02 18.69 4 > 8 22 20 598.08 1 0.02 18.69 4 > > and I need to extract 50% (or rounded) of the rows for each Area (from > Area 1 to 3 only): > > xloc yloc gonad ind Ene W Area > 1 23 20 516.74 1 0.02 20.21 1 > 2 23 20 1143.20 1 0.02 20.21 1 > 4 22 15 251.98 1 0.02 18.69 2 > 6 21 19 250.00 1 0.02 20.21 3
Let me suggest one more solution, which is a modification of the solution by Henrique Dallazuanna pop <- data.frame(Area=c(1,1,1,1,1,2,2,2,2,3,3,3,4,4)) g <- function(x) { seq(along=x) <= ceiling(length(x)/2) } subset(pop, ave(Area, Area, FUN=g) & Area %in% 1:3) Area 1 1 2 1 3 1 6 2 7 2 10 3 11 3 Hope this helps. Petr Savicky. ______________________________________________ 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.