# Separate categories in heatmap colorscale

3 vues (au cours des 30 derniers jours)
Erwan Martin le 5 Sep 2023
Modifié(e) : Voss le 5 Sep 2023
Hello,
I am using a lot heatmaps to illustrate matrices of data such as this one. I often run in the scenario where I could use a data value that would appear similar to NaN but in another color. Here I gave the tiles the value -10 and troncated the colorscale, but I was wondering if anyone knows of a cleaner way to do it because this method is not always optimal.
Thanks !
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### Réponse acceptée

Voss le 5 Sep 2023
Modifié(e) : Voss le 5 Sep 2023
One way would be to put a patch object over the particular cells of the heatmap that you want to be different. Here's a way to do that:
% first, a matrix with some NaN elements:
M = magic(10);
M([1 2 3 11 12 21]) = NaN;
% create the heatmap:
h = heatmap(M);
% color to use to obscure some particular cells of the heatmap:
color = 'w';
% let's say these are the linear indices of the elements in M you
% would replace with -10 (or whatever special value) and color with
% the specified color (I just picked some locations in the lower-
% right of the heatmap):
idx = [70 79 80 86 89 90 95 96 97 98 99 100];
disp(idx(:));
70 79 80 86 89 90 95 96 97 98 99 100
% convert those linear indices to rows and columns:
[m,n] = size(M);
[ridx,cidx] = ind2sub([m,n],idx);
disp([ridx(:),cidx(:)]);
10 7 9 8 10 8 6 9 9 9 10 9 5 10 6 10 7 10 8 10 9 10 10 10
% you can't put a patch into a heatmap chart, so create a new invisible
% axes on top of the heatmap, with the same size, limits, and
% orientation (YDir) as the heatmap:
ax = axes('Units','normalized','Position',h.InnerPosition, ...
'Visible','off','XLim',[0.5 n+0.5],'YLim',[0.5 m+0.5],'YDir','reverse');
% put a patch in the new axes, to obscure those particular cells in the
% heatmap, using the specified color:
xd = 1:n;
yd = 1:m;
patch(ax,xd(cidx)+[0;0;1;1]-0.5,yd(ridx)+[0;1;1;0]-0.5,color)
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