Levelplot in R on irregular grid

Question

I would like to create a 2D levelplot in R where the x and y coordinates are from an irregular grid without using interpolation. The grid is given below:

grid<-cbind(seq(from=0.05,to=0.5,by=0.05),seq(from=0.05,to=0.5,by=0.05))
grid<-rbind(grid,cbind(seq(from=0.0,to=0.95,by=0.05),seq    (from=0.05,to=1,by=0.05)))
grid<-rbind(grid,cbind(seq(from=0,to=0.9,by=0.05),seq (from=0.1,to=1,by=0.05)))
grid<-rbind(grid,cbind(seq(from=0,to=0.85,by=0.05),seq(from=0.15,to=1,by=0.05)))
grid<-rbind(grid,cbind(seq(from=0,to=0.75,by=0.05),seq(from=0.25,to=1,by=0.05)))
grid<-rbind(grid,cbind(seq(from=0,to=0.80,by=0.05),seq(from=0.20,to=1,by=0.05)))
grid<-rbind(grid,cbind(seq(from=0,to=0.70,by=0.05),seq(from=0.30,to=1,by=0.05)))
grid<-rbind(grid,cbind(seq(from=0,to=0.65,by=0.05),seq(from=0.35,to=1,by=0.05)))
grid<-rbind(grid,cbind(seq(from=0,to=0.60,by=0.05),seq(from=0.40,to=1,by=0.05)))
grid<-rbind(grid,cbind(seq(from=0,to=0.55,by=0.05),seq(from=0.45,to=1,by=0.05)))
grid<-rbind(grid,cbind(seq(from=0,to=0.50,by=0.05),seq(from=0.50,to=1,by=0.05)))
grid<-rbind(grid,cbind(seq(from=0,to=0.40,by=0.05),seq(from=0.60,to=1,by=0.05)))
grid<-rbind(grid,cbind(seq(from=0,to=0.45,by=0.05),seq(from=0.55,to=1,by=0.05)))
grid<-rbind(grid,cbind(seq(from=0,to=.35,by=0.05),seq(from=0.65,to=1,by=0.05)))
grid<-rbind(grid,cbind(seq(from=0,to=0.30,by=0.05),seq(from=0.70,to=1,by=0.05)))
x=grid[,1]
y=grid[,2]

The Z-values are stored in another vector. I have tried to use the image-function, but without any luck. For instance, if I try

image(x,y,height.vals)

where

    height.vals=matrix(runif(dim(grid)[1]),nrow=dim(grid)[1],ncol=1)

I get an error message saying that x and y should be increasing.

One could use the akima function interp, but then I get interpolated data.

Answer 1

Looks like you have points on a 20 x 20 grid. So, you can create a 20 x 20 matrix and fill it with the values from height.vals .

With a little bit of tweaking, you can turn the x and y values into indices of the matrix and use those indices to assign height.vals to the appropriate places in the matrix.

# Turn the x and y values into integers.
# R doesn't take 0 as an index, so add 1 to the x values to get rid of the 0s
inds <- cbind(x = as.integer(20*x + 1), y = as.integer(20*y))

# create the 20 x 20 matrix
m <- matrix(nrow = 20, ncol = 20)
# fill the matrix with height.vals based on the indices
m[inds] <- height.vals

Then, you can use m as an input to functions like image , filled.contour , and lattice::levelplot

image(m)