How to plot different parts of one vector with different colors?

Hello. I have a time vector and ecg vector on y axis which need to be plotted in the same figure with 3 different colors. There are three different zones (time before), suspicious zone in the middle (which I want to be yellow) and time after. How can it be plotted? I tried to plot like in the code below, but it can't be plotted like that.

if true
  time1colored(1) = time1(1:523);
  time1colored(2) = time1(524:704);
  time1colored(3) = time1(705:end);
  rr3colored(1) = rr3(1:523);
  rr3colored(2) = rr3(524:704);
  rr3colored(3) = rr3(705:end);
  colors='gyr';
  figure; cla;
  for i=1:3
    plot(time1colored(1),rr3colored(1), 'Color', colors(i))
  end

    plot(time1,rr3)
    xlabel('time [s]'),ylabel('interval [ms]')
end

Answer 1

[James Tursa]

Something like this if you go with the segmented approach:

ix = { 1:523, 524:704, 704:numel(time1) };
colors = 'gyr';
figure; cla;
for i=1:3
    plot(time1(ix{i}),rr3(ix{i}),'Color',colors(i)); hold on
end

[miki90]

Yes, you made it more elegant than I did it a couple of minutes ago. I separated the vector in 3 segments and plotted it in one function. Thank you so much!

[Vidz]

gives error as runs out of colors

Index exceeds the number of array elements (3).

So, I did

plot(time1(ix{i}),rr3(ix{i}),'Color',[rand rand rand]); hold on

[Walter Roberson]

The color list is hardcoded by way of

colors = 'gyr';

You can expand that to include any of the 8 color codes bcgkmrwy

If you need more than that, then I suggest using one of the color tables, such as

ctab = copper(23);
[...]
plot(time1(ix{i}), rr3(ix{i}), 'Color', ctab(i,:)); hold on

Answer 2

[Walter Roberson]

This is not possible in MATLAB using plot() or related calls. plot() and related calls use line() objects, and line() objects are restricted to a single color.

You can break the vector into segments and draw the segments separately.

If you look in the File Exchange you will find a couple of different contributions for drawing colored lines.

[miki90]

Your idea is also good and worked for me. Thanks!

Answer 3

[miki90]

Sorry for posting on an answered post, but, applying this code to plotting with markers, I haven't got only markers but the points connected with lines too. Can anyone tell me why?

if true
  ip = { 1:523, 524:824, 824:numel(rr4) };
colors = ['g*','y*','r*'];
figure(); cla;
for i=1:3
  plot(rr4(ip{i}),rr5(ip{i}),colors(i)); hold on
end
end

[James Tursa]

Use a cell array for your colors and dereference it using curly { } braces. The way you are doing it now colors is a simple char array and colors(i) is only one character of that array. E.g.,

colors = {'g*','y*','r*'}; % <-- curly braces
figure(); cla;
for i=1:3
  plot(rr4(ip{i}),rr5(ip{i}),colors{i}); hold on  % <-- curly braces
end

[miki90]

I guess I will have to read Matlab theory a lot more. Thanks a lot, once again.

[James Tursa]

You could have used your char array as is, but you would have to change that colors(i) to colors(i,:). I think this makes the code a bit harder to read, and also your construction of colors depends on all of your row strings being the same length. The cell array approach looks neater IMO and also allows you to easily use different length char strings for each color if you wanted to.

[Walter Roberson]

Also as well as using colors(i,:) you would have had to use colors = ['g*';'y*';'r*'] and all of the specifications would have had to have been the same length. Your existing colors = ['g*','y*','r*']; is building a single character vector with contents 'g*y*r*' . Using cell arrays is better in this case.

Alternately from R2017a onwards you could stay with your existing code but use colors = ["g*","y*","r*"]; which would not require any change to the indexing you are using.