jiho <jo.irisson <at> gmail.com> writes: > > Hello all, > > I am sure I am missing something obvious but I cannot find the > function I am looking for. I have a data frame with three columns: X, > Y and Z, with X and Y being grid coordinates and Z the value > associated with these coordinates. I want to transform this data > frame in a matrix of Z values, on the grid defined by X and Y (and, > as a plus, fill the X.Y combinations which do no exist in the > original data frame with NAs in the resulting matrix). I could do > this manually but I guess the appropriate function should be > somewhere around. I just can't find it.
I have used xtabs in the past, but xtabs returns 0 instead of NA, which makes great for cross-tabulation, the "offending" line is x[is.na(x)] <- 0. So you would need to either modify the xtabs function or trust that z is never 0 and replace all 0's with NA. > mydat <- expand.grid(x=1:5, y=1:5) > mydat <- data.frame(mydat, z=rnorm(25)) > mydat$z[sample(1:25,4)] <- NA > mytab <- xtabs(z~x+y, mydat) Mark Lyman ______________________________________________ R-help@stat.math.ethz.ch 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.
