Colormap: set color for ranges

I have a matrix that represents a model grid. Non active grid cells are represented by nan within the matrix, cells that don't have data are represented with a zero, and then the rest of the cells are represented with either a positive or a negative number. I want to plot them such that the nan values are all one color, all values that are exactly 0 are one number, values greater than 0 are all one color, and values less than 0 are all one color. I'm at a loss trying to figure out how to do this. Does anyone know how I can accomplish this? Thanks!

Answer 1

[Walter Roberson]

colorid = sign(DataMatrix) + 3;  %negative -> 2, 0 -> 3, positive -> 4
colorid(isnan(colorid)) = 1;

Now nan are 1, negative are 2, 0 are 3, positive are 4. From there you can create 4 x 3 color table such as

colortab = [32 32 32; 0 128 0; 256 0 0; 0 0 0]./256;

image(colorid)
colormap(colortab);

[Colby]

This is fantastic! Simple but yet I wouldn't have ever figured it out. Thanks so much for the help!