# Two similar elements in legend, when they should differ

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Jonne Klockars il 14 Ott 2022
Modificato: Jonne Klockars il 14 Ott 2022
I wrote a function for XOR-problem (below). However, the legend behaviour is weird. First I thought I'd solve it by adding an empty string to the legend (two green discs are plotted), but the problem of legend showing both XOR values as green discs persists. I don't know why the second value (XOR=0) is not a red dicsc in the legend. If someone could point out how to correct the color, I'd appreciate that a lot.
% XOR implemented by projecting the data into third dimension
% returns zero, draws the decision plane in 3D.
function a = XOR3D(data)
z = zeros(3,size(data,2)); % z-axis for the projection
x = data(1,:); % x-coordinates of the data
y = data(2,:); % y-coordinates of the data
for i = 1:size(data,2)
% check if the coordinates are the same or not
if x(i) ~= y(i)
z(:,i) = [0,0,1]'; % XOR = 1
else
z(:,i) = [0,0,2]'; % XOR = 0
end
end
figure;
[X,Y] = meshgrid(2:0.1:3);
Z = repmat(1.5,size(X,1));
mesh(X,Y,Z);
hold on;
% THIS IS GREEN IN THE LEGEND: OK
plot3(2,2,z(z<2),'o','MarkerFaceColor','g','MarkerSize',10);
hold on;
% THIS SHOULD BE RED IN THE LEGEND, NOT GREEN LIKE IT IS NOW
plot3(2,2,z(z>1),'o','MarkerFaceColor','r','MarkerSize',10);
hold on;
plot3(x,y,zeros(4,1),'o','MarkerFaceColor','k','MarkerSize',10);
hold on;
quiver3(2,2,0,0,0,2.21,'r');
hold on;
quiver3(3,3,0,-1.11,-1.11,2.21,'r');
hold on;
quiver3(2,3,0,0,-1.11,1.11,'g');
hold on;
quiver3(3,2,0,-1.11,0,1.11,'g');
title('XOR by projection into the 3rd dimension.');
legend('decision plane z=1.5','XOR=1','','XOR=0');
xlabel('X'); ylabel('Y');
a = 0;
end
Here is an image displaying both XOR values as green discs in the legend:
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### Risposta accettata

Walter Roberson il 14 Ott 2022
plot3(2,2,z(z<2),'o','MarkerFaceColor','g','MarkerSize',10);
That does not mean to draw the selected z values with constant x and constant y, all as a single line. Instead it means to draw numel(z(z<2)) separate lines.
Consider
z2 = z(z<2);
z2xy = 2 * ones(size(z2));
plot3(z2xy, z2xy, z2, 'o', 'MarkerFaceColor', 'g', 'MarkerSize', 10);
##### 1 CommentoMostra -1 commenti meno recentiNascondi -1 commenti meno recenti
Jonne Klockars il 14 Ott 2022
Modificato: Jonne Klockars il 14 Ott 2022
Yep, now it works. Thank you.

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