What are surfA, surfB? There's nothing to suggest that difcount is vectorized so if they are vectors of length > 1 that could lead to your problem.
Michael On Mon, Mar 5, 2012 at 2:07 PM, Colin Wren <[email protected]> wrote: > Hi, > I'm trying to calculate a sum of differences between two ascii grids. > I have the file names of the two grid files in a data.frame along with > other data. I'm then trying to add a new column to the data.frame with > the result of that calculation. > > eg. > > library(maptools) > difcount <- function(surfA, surfB) { > A <- readAsciiGrid(surfA, colname="a") > B <- readAsciiGrid(surfB, colname="b") > sum(A$a - B$b) > } > attach(mydataframe) > difcount(surfA[1],surfB[1]) #this test part works fine and gives me > the correct result > > #But when I try to do a batch job by running the function against each > row of the table it fails > mydataframe["TotalDif"] <- difcount(surfA,surfB) > > Error in file(fname, "r") : invalid 'description' argument > > This error seems to be coming from the readAsciiGrid function, but its > being given the same entry so I don't understand why it fails. Any > ideas? > > Thanks, > Colin > > ______________________________________________ > [email protected] 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. ______________________________________________ [email protected] 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.
