[R] nearest neighbour interpolation
ripley at stats.ox.ac.uk
Fri Jan 31 12:26:03 CET 2003
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, ripley at stats.ox.ac.uk
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
More information about the R-help