Agustin Lobo wrote: > Roger, > > I think that having Arithmetic operations defined for > SpatialGridDataFrame objects would be very useful.
The problem is that SpatialSomethingDataFrame objects don't inherit data.frame's behaviour (with respect to mathematical operators). Perhaps if R's OO implementation was a bit more conventional you'd get this for free by subclassing data.frame. But data.frame isn't subclassable properly. A SpatialPointsDataFrame is an S4 object with a data frame in the @data member. In order to implement data.frame-like behaviour, it is necessary to implement methods for SpatialPointsDataFrame that work on the @data object - for example, dim: dim.SpatialPointsDataFrame = function(x) dim([EMAIL PROTECTED]) It should be almost as equally trivial to implement the arithmetic operators - they would work on the @data member and leave the coordinates untouched. Although what happens to the coordinates if you add two spatial data frames with different coordinates (but the same shape of data frame)? I would be tempted to either make sdf1 + sdf2 return a plain data frame - and if the user wants to slap coordinates on it they can take it from sdf1 or sdf2 - or always use the coords from the first argument. Barry _______________________________________________ R-sig-Geo mailing list R-sig-Geo@stat.math.ethz.ch https://stat.ethz.ch/mailman/listinfo/r-sig-geo
