How to plot the sample mean in a scatter plot?

Hi; Yesterday I had a question about the gscatter command and with the help I got here, I got the results that I wanted:

     % Class 1
        x1 = [16; 18; 20; 11; 17; 8; 14; 10; 4; 7;];
        y1 = [13; 13; 13; 12; 12; 11; 11; 10; 9; 9];
        class1 = [x1 y1];

     % Class 2
        x2 = [8; 9; 6; 8; 5; 7; 4; 6; 4; 3];
        y2 = [8; 7; 7; 6; 5; 5; 4; 3; 2; 2]; 
        class2 = [x2 y2];

    % Class 3
        x3 = [19; 19; 17; 17; 16; 14; 13; 13; 11; 11];
        y3 = [6; 3; 8; 1; 4; 5; 8; 1; 6; 3];
        class3 = [x3 y3];

        figure(1)
        x = [x1;x2;x3];
        y = [y1;y2;y3];
        grp = [ones(size(x1));2*ones(size(x2));3*ones(size(x3))]; % Grouping variableis the class number for each observation in Band 1 and Band 2
        gscatter(x,y,grp,'brg','.xo'), xlabel('Band 1'), ylabel('Band 2'), title('Data of Each Class in a Two-Dimensional Vector Space'), legend('Class 1', 'Class 2', 'Class 3')

Now, I need to plot the sample mean of each class on the plot but I can't seem to find what I'm doing wrong. The code is as follows:

 % b - Compute the sample means and sample covariance matrices for each class and plot the means in the same vector space with the data

    % Class 1        
        M1 = mean(class1) % Sample Mean of Class 1
        C1 = cov(class1)  % Covariance Matrix of Class 1

    % Class 2      
      M2 = mean(class2) % Sample Mean of Class 2
      C2 = cov(class2)  % Covariance Matrix of Class 2

    % Class 3
      M3 = mean(class3) % Sample Mean of Class 3
      C3 = cov(class3)  % Covariance Matrix of Class 3

      figure(2)
      x = [x1;x2;x3];
      y = [y1;y2;y3];
      grp = [ones(size(x1));2*ones(size(x2));3*ones(size(x3))]; % Grouping variableis the class number for each observation in Band 1 and Band 2
      gscatter(x,y,grp,'brg','.xo'), xlabel('Band 1'), ylabel('Band 2'), title('Data of Each Class in a Two-Dimensional Vector Space with the Sample Means')
      hold on
      plot(M1(1,1),M1(1,2),'b')
      hold on
      plot(M2(1,1),M2(1,2),'r')
      hold on
      plot(M3(1,1),M3(1,2),'g'),legend('Class 1','Class 2','Class 3','Mean_Class 1','Mean_Class 2','Mean_Class 3')

The mean of each class is not shown in the figure. How can I plot the sample mean of each class?

Answer 1

[Image Analyst]

You didn't make an appropriate marker. Make the last chunk of your code this, and it will do it.

figure(2)
x = [x1;x2;x3];
y = [y1;y2;y3];
grp = [ones(size(x1));2*ones(size(x2));3*ones(size(x3))]; % Grouping variableis the class number for each observation in Band 1 and Band 2
gscatter(x,y,grp,'brg','.xo');
xlabel('Band 1');
ylabel('Band 2');
title('Data of Each Class in a Two-Dimensional Vector Space with the Sample Means', 'FontSize', 24)
hold on
plot(M1(1,1),M1(1,2), 'b*', 'MarkerSize', 18, 'LineWidth', 2)
plot(M2(1,1),M2(1,2), 'r*', 'MarkerSize', 18, 'LineWidth', 2)
plot(M3(1,1),M3(1,2), 'g*', 'MarkerSize', 18, 'LineWidth', 2)
legend('Class 1','Class 2','Class 3','Mean of Class 1','Mean of Class 2','Mean of Class 3')
grid on;

% Set up figure properties:
% Enlarge figure to full screen.
set(gcf, 'Units', 'Normalized', 'OuterPosition', [0 0 1 1]);
% Get rid of tool bar and pulldown menus that are along top of figure.
set(gcf, 'Toolbar', 'none', 'Menu', 'none');
% Give a name to the title bar.
set(gcf, 'Name', 'Demo by Augustin', 'NumberTitle', 'Off')

[Agustin]

Thank you so much! This was very helpful.