On 31 Jan 2003, Jari Oksanen wrote: > On Fri, 2003-01-31 at 12:47, Roger Bivand wrote: > > On Thu, 30 Jan 2003, Matthew Oliver wrote: > > > > > Dear Help List, > > > > > > My name is Matt Oliver. I have been using R for about a year and find it very > > > helpful. However, I have a need for a function that I cannot find. I am not very > > > good at programming so I thought I would ask the group. > > > > > Maybe this is an opportunity to explore things - they are usually feasible > > if the motivation is sufficiently strong. > > > > > I have an irregular grid of data (x = Longitude, y = Latitude). Each pair of my >x,y > > > has a categorical value. Obviously linear or any other numerically based > > > interpolation on categorical data does not make sense, so I want to use a >nearest > > > neighbor interpolation so that I can extrapolate my irregular grid to a regular >grid > > > of Longitude and Latitude. > > > > > There does not seem to be such a function at present. > > I am not sure if this is an answer to the original question, but package > akima does the following: > > Description: Linear or cubic spline interpolation for irregular > gridded data > > which sounds like something that was asked for.
That's what was explicitly _not_ asked for: it's numerical. Categorical nearest-neighbour interpolation can be done (easily) via knn1 in package class, although it is a bit inefficient for very large grids and there are theoretically faster ways (see my 1981 book, for example). You can do the grid in parts, though. -- Brian D. Ripley, [EMAIL PROTECTED] Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG, UK Fax: +44 1865 272595 ______________________________________________ [EMAIL PROTECTED] mailing list http://www.stat.math.ethz.ch/mailman/listinfo/r-help
