I have a For loop that is quite slow and am wondering if there is a faster option:
df <- data.frame(TreeID=rep(1:500,each=20), Age=rep(seq(1,20,1),500)) df$Height <- exp(-0.1 + 0.2*df$Age) df$HeightGrowth <- NA #intialize with NA for (i in 2:nrow(df)) {if(df$TreeID[i]==df$TreeID[i-1]) {df$HeightGrowth[i] <- df$Height[i]-df$Height[i-1] } } Trevor Walker Email: trevordaviswal...@gmail.com [[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.