How can I change the line color in a 2D graph using colormap?

Hello everyone,

there is a mx5 matrix composed by the following columns:

x1 y1 x2 y2 c

where (x1,y1) and (x2,y2) are respectively the initial e and final coordinates of a link; c is the "color" variable.

I would like to assign a different color to the links according to c, using colormap.

I have already adopted the following solution:

A = rand(10,5);
  c = A(:,5);
  for i=1:10
      x1=A(i,1);
      y1=A(i,2);
      x2=A(i,3);
      y2=A(i,4);
      plot([x1,x2],[y1,y2],'Color', [c(i) 0.2*(1-c(i)) 0.3*(1-c(i))])
      hold on
  end

The result is not satisfying. I would like to use the default colormap, but I know that is not possible to use it with plot. Does anybody know if it is possible to use surf? And how?

I need it for my thesis, any help is appreciated. Thanks a lot! :)

Answer 1

[Star Strider]

I am not certain what result you want.

Try this:

A = rand(10,5);
cm = colormap(parula(size(A,1)));                           % Default Colormap
% c = A(:,5);
for i=1:10
    x1=A(i,1);
    y1=A(i,2);
    x2=A(i,3);
    y2=A(i,4);
    plot([x1,x2],[y1,y2],'Color', cm(i,:))
    hold on
end

[alex mango]

Thank you, but not really what I want. I want to use the parameter "c" to discriminate the RGB triplet. So, if two links have the same "c", they must have the same color. Did I explain myself?

Thanks for any help.

[Star Strider]

That wasn’t part of your original Question, and all your data are random here.

I would use either sort, using the third output to define the colours, (or sortrows using the second output to define them, although you may have to use unique on the ‘index’ output of sortrows as well).

Determine the number of unique items as the length of the first output, define a colormap with that number of colours, then use the third output of unique to define the colours.

[alex mango]

Could you explain with an example please?

[Star Strider]

I still have no idea what you want.

This creates a random matrix, then colours every line defined by the first 4 columns with the colour defined for it in the 5-th column. Note that the 5-th column must be an integer for this to work, so if they are not, you have to define them as integers. The unique function will do that.

Example —

M = rand(20, 5);                                                    % Create Matrix
[Cu,~,Idx] = unique(M(:,5), 'stable');                              % Find Unique Elements Of Col #5, Return Index, Don’t Sort
cm = colormap(jet(max(Idx)));                                       % Define ‘colormap’

figure(1)
for k1 = 1:size(M,1)
    plot(M(k1,[1 3]), M(k1,[2 4]), 'Color',cm(Idx(k1),:), 'LineWidth',2)
    hold on
end

[alex mango]

That's exactly what I wanted. Thank you very much for your help and for your patience.

[Star Strider]

As always, my pleasure.

If my Answer helped you solve your problem, please Accept it!