Exclude prediction grid points too far from data
Takes two arrays defining the nodes of a grid over a 2D covariate space and two arrays
defining the location of data in that space, and returns a logical vector with elements TRUE if
the corresponding node is too far from data and FALSE otherwise. Basically a service routine for
vis.gam and plot.gam.
exclude.too.far(g1,g2,d1,d2,dist)
g1 |
co-ordinates of grid relative to first axis. |
g2 |
co-ordinates of grid relative to second axis. |
d1 |
co-ordinates of data relative to first axis. |
d2 |
co-ordinates of data relative to second axis. |
dist |
how far away counts as too far. Grid and data are first scaled so that the grid lies exactly
in the unit square, and |
Linear scalings of the axes are first determined so that the grid defined by the nodes in
g1 and g2 lies exactly in the unit square (i.e. on [0,1] by [0,1]). These scalings are
applied to g1, g2, d1 and d2. The minimum Euclidean
distance from each node to a datum is then determined and if it is greater than dist the
corresponding entry in the returned array is set to TRUE (otherwise to FALSE). The
distance calculations are performed in compiled code for speed without storage overheads.
A logical array with TRUE indicating a node in the grid defined by g1, g2 that
is ‘too far’ from any datum.
Simon N. Wood simon.wood@r-project.org
library(mgcv) x<-rnorm(100);y<-rnorm(100) # some "data" n<-40 # generate a grid.... mx<-seq(min(x),max(x),length=n) my<-seq(min(y),max(y),length=n) gx<-rep(mx,n);gy<-rep(my,rep(n,n)) tf<-exclude.too.far(gx,gy,x,y,0.1) plot(gx[!tf],gy[!tf],pch=".");points(x,y,col=2)
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