Highlight cells in heatmap

xvalues = 1:5;
yvalues = 1:5;
cdata = randi(20,[5,5]); % range of values in cells < 20
cmap = [repmat([1 0 0],5,1)
    repmat([1 1 1],5,1) % highlight all cells with values from 5-10 with white
    repmat([0 0 0],10,1)]; % highlight all cells > 10 with black
heatmap(1:5,1:5,randi(20,[5 5]),'Colormap',cmap);

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Ilyass Boukhari 2020-12-1

在 MATLAB Online 中打开

Hey Rishik thanks for your help!

I tried replace your example values with my array size and values, so that it would fit my actual needs

xvalues = 1:25 ; 
yvalues = 1:25
 
cdata = 
 100   100   100   100   100   100   100   100
 300   300   300   250   200   180   150   100
 500   500   300   250   200   180   150   100
 500   450   300   250   200   180   150   100
 600   500   400   300   200   180   150   100
 700   600   500   300   200   180   150   100
 600   500   450   400   200   180   150   100
 500   400   300   250   200   180   150   100
 450   450   300   300   250   200   150   100
 450   450   550   450   250   230   200   100
 450   550   700   700   250   230   200   100
 300   500   650   650   250   200   150   100
 300   400   450   300   250   200   150   100
 380   380   380   300   250   200   150   100
 350   380   380   300   250   200   150   100
 500   350   390   300   300   200   150   100
 400   370   350   300   300   200   150   100
 400   360   350   300   300   200   150   100
 300   350   350   300     0   200   150   100
 200   200   200   200   100   100   100   100
 100   100   100   100   100   100   100   100
 100   100   100   100   100   100   100   100
 100   100   100   100   100   100   100   100
 250   250   250     0     0     0     0   100
 100   100   100   100   100   100   100   100 
 
cmap = [repmat([0 0 0],200,1 ) %black background
    repmat([1 1 1],200,1) % highlight all cells with values from 200-750 white 
    repmat([1 0 0],750,1)]; % highlight all cells > 750 with red (highest)
 
heatmap(1:25,1:25,cdata,'Colormap',cmap);

however this is the result (as you can see the map doesn't reflect the aimed ranges)

What am I doing wrong?

Your help is much appreciated

Rishik Ramena 2020-12-1

编辑：Rishik Ramena 2020-12-1

在 MATLAB Online 中打开

The second argument for repmat denotes the number of rows to be repeated for the RGB vector given in its first argument. So the cmap contains rows of RGB values which are equal in number to the range of values in the cdata (max-min). For visualisation, try imagining filling the colors on the colorbar from the bottom while creating a custom colormap.

max_val = max(cdata(:)) % get the max value from cdata
cmap = [repmat([1 0 0],200,1) % first 200 rows (0-199)
repmat([1 1 1],750-200,1) % 200-749
repmat([0 0 0],max_val-750,1)]; % >= 750