[R] image() plot with z not in matrix format

[mdgi at gmx.ch]

Hello R cracks

The image() function requires strictly increasing x and y values and z as a matrix.

Actually, I don't have equally spaced variables, but anyway want to plot an colored image() (with z-information).

An example of my problem is here:

a<-data.frame(rnorm(100), rnorm(100), runif(100)*100)

How can I plot this data as an image (x=a[,1], y=a[,2] and z=a[,3])-> according to ?image.
It has to be possible to adapt the grid size so that every grid cell in the plot is coloured consequently.

Thanks for your help

Marc
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