Loop with Different Colors in Array using Line function in MATLAB

Question

I have created an array of colors to loop over when outputting different plots.

Somewhere in the code it is broken. I am getting no errors, but yet the colors output does not represent the color array. It outputs the last color in the array for all lines in the color black.

figure1 = figure('Color','w');

apples = [3 5 6 3 2]
oranges = [2 3 4 5 6]
grapes = [3 4 3 2 5]
count = [1 2 3 4 5]


C = {'b','r','g','m','k'} 
hold on
for i = 1:5

line(count, apples, 'LineStyle','-','LineWidth', 2, ...
        'Marker','x', 'MarkerSize',10, 'Color',C{i},'DisplayName','apples');

  line(count, oranges, 'LineStyle','-', 'LineWidth', 2, ...
        'Marker','.', 'MarkerSize',10, 'Color',C{i},'DisplayName','oranges');  

line(count, grapes, 'LineStyle','-', ...
        'Marker','.', 'MarkerSize',10, 'Color',C{i},'DisplayName','grapes' );
end
hold off

I see you're plotting 3 lines. Why does color index i range from 1 to 5? — SecretAgentMan
– SecretAgentMan, Commented Mar 27, 2019 at 17:43
Yes, you told MATLAB to plot each line in every color, and black was the last one so it's on top. What did you want it to do? — beaker
– beaker, Commented Mar 27, 2019 at 17:44
@beaker, I need to plot the first line with color blue, second line with color red, and third line with color green. — Minimalist
– Minimalist, Commented Mar 27, 2019 at 17:46
Then remove the loop and change C{i} to C{1}, C{2} and C{3}. You've already duplicated the plot statements, you don't need to repeat them again. — beaker
– beaker, Commented Mar 27, 2019 at 17:48
I need the loop for future growth of more plots. More automated. — Minimalist
– Minimalist, Commented Mar 27, 2019 at 17:50

SecretAgentMan · Accepted Answer · 2019-03-27 18:11:56Z

Issue: As alluded to in my comment, your index i ranges from 1 to 5 and inside said loop you plot three lines each time (15 total lines). Each iteration is changing plotting three lines with the same color (first blue, then red, and so on).

Solution:
General approach is to separate the plot and the plot properties in organized way that automates desired portions.

Automate color: Code below uses a matrix of RGB values called Cmat.
Common line properties: Common plot properties (all lines) adjusted with for loop.
Individual line properties: Specific line properties adjusted via switch statement.

I generally like to leave the DisplayName with the plot call just for readability but that's my preference, especially if variable names are more abstract.

% MATLAB R2017a
figure1 = figure('Color','w');
hold on 

apples = [3 5 6 3 2];
oranges = [2 3 4 5 6];
grapes = [3 4 3 2 5];
count = [1 2 3 4 5];


% C = {'b','r','g','m','k'} 
Cmat = [0 0 1; 1 0 0; 0 1 0; .8 0 .2; 0 0 0];   % use a matrix of RGB values

p(1) = plot(count,apples,'DisplayName','apples')      % give plots handles
p(2) = plot(count,oranges,'DisplayName','oranges')
p(3) = plot(count,grapes,'DisplayName','grapes')

% Cosmetics
for j = 1:3                  
    p(j).LineStyle = '-';        % Common plot property adjustments
    p(j).LineWidth = 2;
    p(j).MarkerSize = 10;
    p(j).Color = Cmat(j,:);
    switch j                     % Specific plot property adjustments
        case 1
            p(j).Marker = 'x';   % Marker type for 1st line
        case 2 
            p(j).Marker = '.';
        case 3
            p(j).Marker = '.';
    end
end    
% legend('show')    % include legend

Undoubtedly there are more efficient solutions. I encourage OP and future readers to also see this excellent answer from @gnovice.

gnovice · Accepted Answer · 2019-03-27 18:06:54Z

3

Your problem is that you are replotting all three of your lines repeatedly, each time with a different color, the last time with black. You should either plot each line without a loop like this:

line(count, apples, 'LineStyle', '-', 'LineWidth', 2, ...
     'Marker', 'x', 'MarkerSize', 10, ...
     'Color', C{1}, 'DisplayName', 'apples');
line(count, oranges, 'LineStyle', '-', 'LineWidth', 2, ...
     'Marker', '.', 'MarkerSize', 10, ...
     'Color', C{2}, 'DisplayName', 'oranges');
line(count, grapes, 'LineStyle', '-', ...
     'Marker', '.', 'MarkerSize', 10, ...
     'Color', C{3}, 'DisplayName', 'grapes');
              % ^
              % Note this difference

Or call line once inside a loop like this:

data = {apples, oranges, grapes};         % Cell array of your y data
markers = {'x', '.', '.'};                % Cell array of your markers
names = {'apples', 'oranges', 'grapes'};  % Cell array of your names

for iLine = 1:numel(data)
  line(count, data{iLine}, 'LineStyle', '-', ...
       'Marker', markers{iLine}, 'MarkerSize', 10, ...
       'Color', C{iLine}, 'DisplayName', names{iLine});
end

A third option is to update the ColorOrder property of the axes so that it automatically (and repeatedly) cycles through your preferred colors (defined as RGB triples). Note that you'll have to use plot instead of line to create your lines this way:

C = [0 0 1; 1 0 0; 0 1 0; 1 0 1; 0 0 0]; 
set(gca, 'ColorOrder', C);

hold on;
plot(count, apples, 'LineStyle', '-', 'LineWidth', 2, ...
     'Marker', 'x', 'MarkerSize', 10, 'DisplayName', 'apples');
plot(count, oranges, 'LineStyle', '-', 'LineWidth', 2, ...
     'Marker', '.', 'MarkerSize', 10, 'DisplayName', 'oranges');
plot(count, grapes, 'LineStyle', '-', ...
     'Marker', '.', 'MarkerSize', 10, 'DisplayName', 'grapes');

edited Mar 27, 2019 at 18:06

answered Mar 27, 2019 at 17:51

gnovice

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2 Comments

Minimalist Over a year ago

gnovice really nice explanation.

SecretAgentMan Over a year ago

Nice! Didn't know about ColorOrder property adjustment option. Thanks for sharing. Very succinct options. (+1)

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