On Sat, 14 Jul 2007, Michal Gallay wrote: > Dear R Users, > > could you please advise me on doing map algebra with spatial grids? It's > the first time I am using spatial objects in R. I have imported an ascii > grid file and wanted to round the values in it or sum with a value, but it > gives an error message: > >> require(maptools) >> x <- readAsciiGrid(fname="xxxx.asc") >> x+3 > Error in x + 3 : non-numeric argument to binary operator >> round(x,2) > Error in round(x, digits) : Non-numeric argument to mathematical function >
Arithmetic operations are not defined for SpatialGridDataFrame operations, as the columns of the data frame (here a single column) may contain data of different classes. Do the operations on the columns directly: names(x) If there is a column called "band1", then x$band1 + 3 will print "band1" + 3, and x$band1 <- x$band1 + 3 will add 3 to the "band1" column. Think what would happen if band1 was categorical or logical to see why doing arithmetic directly isn't such a good idea. Hope this helps, Roger > Thank you for any suggestions. > > Best wishes, > > Michal > > > > -- Roger Bivand Economic Geography Section, Department of Economics, Norwegian School of Economics and Business Administration, Helleveien 30, N-5045 Bergen, Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43 e-mail: [EMAIL PROTECTED] _______________________________________________ R-sig-Geo mailing list R-sig-Geo@stat.math.ethz.ch https://stat.ethz.ch/mailman/listinfo/r-sig-geo
