Using imagesc to make a matrix a heatmap, how can I mark an 'x' inside the cell of max value of each column?

I have created a checkerboard heatmap with imagesc, using 9 subplots for an 11x11x9 array. I would like to clearly denote the 'maximum value' in each column with a red 'x' placed inside the center of each cell.

Below is the code I run to (successfully) generate the subplots. The commented section is my failed attempt to start drawing these 'x' markers - hoping for some help. Thank you!

[max_val, ~] = max(cond_npvnetrevcumlist_btfc0_417_extinct(:));
maxcaxis = max_val;
[min_val, ~] = min(cond_npvnetrevcumlist_btfc0_417_extinct(:));
mincaxis = min_val;
figure
for k=1:9
    subplot(3,3,k)
    C=cond_npvnetrevcumlist_btfc0_417_extinct(:,:,k);
    I=imagesc(C);
    %colorbar
    title(['Initial Bt Resistance Alleles=' num2str(InitResistList(k)*100) '%'])
    ylabel('% Bt Planted') 
    xlabel('GM DBM release rates')
    ticknumx = linspace(0,12,13);
    ticknumy = linspace(0,11,12);
    set(gca,'xtick',ticknumx,'ytick',ticknumy)
    xticklabels({'0','0', '0.5', '1', '1.5', '2', '4', '6', '10', '15', '20', '40'})
    yticklabels({'0','0','10','20','30','40','50','60','70','80','90','100'})
    c=colorbar;
    c.Label.String = '% Max Revenue, net seed+releases';
    caxis([mincaxis,maxcaxis])  %Engage to equate across all colorbar values; makes it harder to see the max within each matrix though
%         %Failed attempt thus far to draw an 'x' in the centroid of the matrix cell of each column maximum value
%         markers = zeros(11,1);
%         for m=1:11
%             [~, max_val_col] = max(cond_npvnetrevcumlist_btfc0_417_extinct(:,m,k));
%             markers(m)= max_val_col;
%         end
%         pos=zeros(11,2);
%         for n=1:11
%             pos(n,1)=n;
%             pos(n,2)=markers(n);
%         end
%         color={'magenta'};
%         RGB=insertMarker(I,pos,'x','color',color);       
end

Answer 1

[Adam Danz]

Here's a simpler version that uses an "X" in text format. Just replace my fake "C" with your real data.

C = magic(9); 
I = imagesc(C); 

% Find row with max val for each col
[~, maxRowIdx] = max(I.CData,[],1); 

% Assign text
text(1:size(C,2), maxRowIdx, repmat({'X'},size(maxRowIdx)), ...
    'VerticalAlignment', 'Middle','HorizontalAlignment', 'Center', ...
    'FontSize', 14, 'FontWeight', 'Bold')

If your columns and rows start at values other than 1, you'll need to slightly adapt this by offsetting the (x,y) coordinates. use the I.XData and I.YData for rescaling the coordinates.

[Michael Jones]

Thank you, Adam! Worked like a charm. I love the approach.

[Adam Danz]

Great, glad I could help!