Explicitly specifying line colors when plotting a matrix

x = 1:3;
y = [1 2 3; 42 40 34];
plot(x,y,'Color', [0.5 0.5 0.5; 1 0 0])

produce an error:

Error using plot
Color value must be a 3 element numeric vector

Same with:

plot(x,y,'rg')
Error using plot
Error in color/linetype argument

This has bugged me for years, but I have circumvented it by unrolling the matrix into a number of vectors that I plot one at a time using whatever color I prefer. But is there no way to tell MATLAB (in a compact, readable form) what colors I would like it to use for whatever number of lines it will plot?

[ELTH]

You can make a for loop and specify each line's colour based on the RGB code:

x = 1:3;
y = [22 20 18; 32 30 24; 42 40 34];
figure
hold on
for k=1:size(y,1)
  p(k)=plot(x,y(k,1:end),'LineWidth',2); 
  set(p(k),'Color',[(size(y,1)-k+1)/size(y,1) k/size(y,1) 0.1]);
end

Answer 1

[Kelly Kearney]

An alternative method would be to save the handles of the plotted data and set the colors via the array option of set. I find this method a lot less hassle than messing with ColorOrder and hold states:

x = 1:3;
y = [1 2 3; 42 40 34];
h = plot(x,y);
set(h, {'color'}, {[0.5 0.5 0.5]; [1 0 0]});

I often use the shortcut of using a colormap with num2cell to get the desired list of colors:

set(h, {'color'}, num2cell(jet(2),2));

[Alexei M]

Dear Kelly (or anyone else reading this),

Could you please "unpack" this answer a bit more? This method is exactly what I'm looking for, because I'm creating line plots with something like 50-100 curves at a time, and I want the colors between each curve to vary sequentially, from first to last curve in the data set. Hence, using a colormap is perfect. I got it to work by following your template and changing the argument in jet() to the total number of curves that I'm plotting.

However, I don't quite get why it's necessary to use cells in the argument of the set() function.

[Image Analyst]

I believe I answered your question in my demo attached in the 3rd (hidden) comment above: https://www.mathworks.com/matlabcentral/answers/19815-explicitly-specifying-line-colors-when-plotting-a-matrix#comment_241391 Show all the comments and look for colororder_demo. Actually, I'm just going to attach them here again.

[Kelly Kearney]

The cell arrays are used because I'm using the cell array syntax for set, as described in the help text for that function (third option):

"set(H,pn,pv) sets the named properties specified in the cell array of strings pn to the corresponding values in the cell array pv for all objects specified in H. The cell array pn must be 1-by-N, but the cell array pv can be M-by-N where M is equal to length(H) so that each object will be updated with a different set of values for the list of property names contained in pn."

I could also set multiple properties using this syntax:

set(h, {'color', 'linewidth'}, [num2cell(jet(2),2) num2cell((1:length(h))')]);

[Xi Guo]

Thanks for sharing! It is extremely helpful!

[Chien-Han Su]

I regret for not seeing this earlier! Thank you for sharing!

Answer 2

[Image Analyst]

In the help it says this:

"plot automatically chooses colors and line styles in the order specified by ColorOrder and LineStyleOrder properties of current axes. ColorOrder : m-by-3 matrix of RGB values

Colors to use for multiline plots. Defines the colors used by the plot and plot3 functions to color each line plotted. If you do not specify a line color with plot and plot3, these functions cycle through the ColorOrder property to obtain the color for each line plotted. To obtain the current ColorOrder, which might be set during startup, get the property value:

get(gca,'ColorOrder')

Note that if the axes NextPlot property is replace (the default), high-level functions like plot reset the ColorOrder property before determining the colors to use. If you want MATLAB to use a ColorOrder that is different from the default, set NextPlot to replacechildren. You can also specify your own default ColorOrder."

co = get(gca,'ColorOrder') % Initial
% Change to new colors.
set(gca, 'ColorOrder', [0.5 0.5 0.5; 1 0 0], 'NextPlot', 'replacechildren');
co = get(gca,'ColorOrder') % Verify it changed

% Now plot with changed colors.
x = 1:3;
y = [1 2 3; 42 40 34];
plot(x,y, 'LineWidth', 3);

The things I put in the set() command are especially important.

[Stefanos]

Thank you, really helpful.

[Andrew Reibold]

3 years later this answer is still helping people. :)

[Image Analyst]

Here's something that will probably be even more helpful. I'm attaching my colororder demo to show you how you can change the default colors to whatever you want.

[Kwon]

oh, it's work on subplot, too thank you~

[Cici Ma]

A note for subplot: need to put the set line before each plot command

x = 1:3;
y1 = [1 2 3; 42 40 34];
y2 = [3 5 8; 11 17 29];
subplot(2,1,1);
set(gca, 'ColorOrder', [0.5 0.5 0.5; 0.2 0.2 0.2],'NextPlot', 'replacechildren');
plot(x,y1, 'LineWidth', 3);
subplot(2,1,2);
set(gca, 'ColorOrder', [0.5 0.5 0.5; 0.2 0.2 0.2],'NextPlot', 'replacechildren');
plot(x,y2, 'LineWidth', 3);

And much appreciated to Image Analyst!

[KAE]

And if you need to restore the color order to the defaults, use reset(gca).

Answer 3

[Daniele Maddaluno]

I can solve your problem with something like this:

x = 1:5;
y = [x; x.^2; x.^3; x.^4; x.^5];
n = size(y, 1);

colors = hsv(n);
h = plot(x, y);
set(h, {'color'}, num2cell(colors, 2));

[rosa agliata]

just great! thanks a lot!

[Vivek Bhardwaj]

Hi, works perfectly, thank you. I have a follow-up question to this. Is it possible that I can have the colors based on a different data set? i.e. I use X and Y only for plotting but the colors of the plot are based on data set, say P (Pressures).

Answer 4

[Joakim Wang Erlandsson]

It is beyond me how matlab manages to be so unintuitive in the most simple sitiations. Luckily there is a smart community that can find workarounds for all of these shortcomings. Someone above stated happily that this answer is still helping people years after it was asked, too me this is just sad, that Mathworks haven't improved this in all of that time.

[Jim Camp]

Joakim, I partially agree with you. In my (limited) experience, MATLAB is much more intuitive than its competitors. If you think MATLAB is difficult, try R! However, this example shows that there is plenty of scope for improvement.