Plotting a figure, with the color of the plot based on a secondary variable

Hello,

I'd like to plot a dataset against an angle theta, where the dataset is a 91x2 double which is inside of a struc, with the first column being the datapoint and the second column being a number corresponding to the datapoints nature. For my case I'm examing the failure of a composite lamina and the number in the second column corresponds to failure due to tension/shear/compression. The number in the first column is the strength of the lamina at failure

This is being plotted against an angle theta ranging from 0 to 90 degrees for 91 points total.

I want the plot line to be red when the second column of my dataset is equal to a value, lets say 115, and blue when the second column of my dataset equals 116.

This is part of a subplot where r and c are 5 and 4 respectively.

subplot(r,c,13)
hold on
for i = 1:91
    if fail.sigmault(i,2) == 115
        plot(theta,fail.sigmault(i,1),'r')
    elseif fail.sigmault(i,2) == 116
        plot(theta,fail.sigmault(i,1),'b')
    end
end

When running the above, I get an empty graph and I'm not sure whats wrong here, I'd appreciate the help.

Answer 1

[Walter Roberson]

plot() does not have the ability to plot an individual line with different colors for different vertices. I suggest

plot(theta, fail.sigmault(:,1));
hold on

markersize = 15;
markercolor = repmat([1 0 0], numel(theta), 1);
mask = fail.sigmault(:,2) == 116;
markercolor(mask,:) = repmat([0 0 1], nnz(mask), 1);
scatter(theta, fail.sigmault(:,1), markersize, markercolor, 'fill');

hold off

This particular code assumes the marker color should be red except where it is blue. The code would be slightly different for the case where you wanted red for 115, blue for 116, and no marker for other colors.

[David Argueta]

Would it be possible to have this work for additional values in the second column? Say another number being 99 in the third column to have a third color applied to that section?

[Walter Roberson]

This version will only mark the vertices that have one of the special values. It would not be difficult to have a default color for the entries that do not match the ones in the list.

plot(theta, fail.sigmault(:,1));
hold on

markersize = 15;

special_values = [99, 115, 116];
colortable = [0 1 0;  %green
              1 0 0;  %red
              0 0 1]; %blue
[markthis, colidx] = ismember(fail.sigmault(:,2), special_values);
nummatches = nnz(markthis);

markercolor = colortable(colidx(markthis), :);

scatter(theta(markthis), fail.sigmault(markthis,1), markersize, markercolor, 'fill');

hold off

[Walter Roberson]

Or... you could do the plot() and then use gscatter