MATLAB Answers

Colormap for multline plot

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Matt
Matt on 25 Feb 2020
Commented: Walter Roberson on 31 May 2021 at 7:46
How do I change the colormap of a multiline plot and have it change the colors of the existing lines? I am using Matlab 2018b. Here is a simple example.
x = rand(10,1000);
t = 0:999;
plot(t, x)
colormap winter
colormap white
colormap flag
fh = gcf;
fh.Colormap = colormap('flag');
fh.Children(1).Colormap = colormap('flag');
For me, the colors of the lines do not change. The following also did not work, the lines are plotted using the "default" color scheme.
fh2 = figure;
fh2.Colormap = colormap('flag');
ax = axes(fh);
ax = axes(fh2);
ax.Colormap = colormap('flag');
plot(ax, t, x)
Invoking "colorbar" shows a colorbar using the desired colormap. Using colormap with surf(peaks) does change the color of that plot. How do I change the colormap of a 2D multiline plot?

Accepted Answer

Bhaskar R
Bhaskar R on 25 Feb 2020
"A colormap is matrix of values between 0 and 1 that define the colors for graphics objects such as surface, image, and patch objects. MATLAB® draws the objects by mapping data values to colors in the colormap." from https://in.mathworks.com/help/matlab/ref/colormap.html
But you are trying to apply colormap to line data instead of surface, image, patch data objects.

More Answers (2)

Sindar
Sindar on 25 Feb 2020
Edited: Sindar on 25 Feb 2020
I believe this should work:
mylines = plot(t, x);
set(mylines,{'Color'},flag(length(mylines)))
For 2019b+, colororder is the function that controls this. I think the way you'd pass a colormap is
colororder(flag)
but you might need
colororder(flag(100))
  4 Comments
Walter Roberson
Walter Roberson on 31 May 2021 at 7:46
mylines = plot(t, x);
set(mylines,{'Color'}, num2cell(flag(length(mylines)),2))
when you use a cell array of parameter names, like {'Color'}, then you need a cell array of values to set.
This is an appropriate way to set the entries to different colors.
If you were to try
set(mylines, 'Color', something)
then that would be attempting to set the Color parameter of all the entries in mylines to the same value stored in something -- for example, 'Color', 'g' to set them all to green.

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Walter Roberson
Walter Roberson on 25 Feb 2020
line() colors are not affected by the colormap, ever. They are affected by the axes ColorOrder property.
In the release you are using, changing the ColorOrder property never affects lines that have already been drawn: you have to set the Color property of each of the line() objects that already exists.
Starting in r2019b, there is a new colororder() function that can set the axes ColorOrder property. As well, by default changing the ColorOrder will affect lines that have already been drawn. (I do not recall at the moment how to turn that off)
  1 Comment
Matt
Matt on 25 Feb 2020
Looks like another reason to roll to the newer release. After reading the documentation tagged to the functions you mention I saw this wonderful statement "Changing the order has no effect on existing plots. However, many graphics functions reset the color order back to the default value before plotting."

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