Matlab - plotting function with a for loop over a matrix - matlab

Question

I have an assignment which sounds like:
"“Grades per assignment”: A plot with the assignments on the x-axis and the grades on the y-axis. The x-axis must show all assignments from 1 to M, and the y-axis must show all grade −3 to 12. The plot must contain:
Each of the given grades marked by a dot. You must add a small random number (between -0.1 and 0.1) to the x- and y-coordinates of each dot, to be able tell apart the different dots which otherwise would be on top of each other when more than one student has received the same grade in the same assignment.
The average grade of each of the assignments plotted as a line"
For now i have created this function:
function gradesPlot(grades)
figure(2);
n_assignments=size(grades,2);
hold on; % Retain current plot when adding new plots.
for i = 1:n_assignments % Loop through every assignment.
% Scatter plot of assignment vs grades for that assignment.
% One assignment on every iteration.
n_assignments2=([1:size(grades,2)]);
scatter(n_assignments2,grades(:,i)'jitter', 'on', 'jitterAmount', 0.1)
hold off; % Set the hold state to off.
end
%Titles to the plot
title('Grades per assignment');
xlabel('Assignment');
ylabel('Given grades');
break;
end
when i run the code it says that the vectors must be same length.
And it looks like it doesn't loop over the matrix more than ones.
The test grades i am using as input is looking like this:
grades=[[-3,4,10];[7,4,12];[7,10,12];[0,4,4];[2,2,2];[2,2,2]]
I hope some of you guys can help me get this function to work - maybe in an easier way?
Thank you in advance

Answer 1

You should not turn off hold since it is tells MatLab to plot everything in the current active plot, roughly speaking. You can find a possible solution to your problem down below: I added some explanations in comments.
function gradesPlot(grades)
figure(2);
% Extract the relevant information: number of assignements, number of grades
[n_assignments,n_grades] = size(grades);
hold on; % Retain current plot when adding new plots.
for i = 1:n_assignments % Loop through every assignment.
% Scatter plot of assignment vs grades for that assignment.
% One assignment on every iteration
% For Scatter, you have to provide 2 vectors of the same size: in this
% way, we are putting al the dots corresponding to the grades of the
% i-th assignement in correspondence of the i-th coordinate on the x
% axis. We are also temporary saving in h the handle to the attributes
% of the dots, in order to retrieve the color.
h = scatter(i*ones(n_grades,1),grades(i,:),'jitter', 'on', 'jitterAmount', 0.1);
% This plots the horizontal line corresponding to the average of the
% grades related to the i-th assignement
l = line([i-0.5 i+0.5],[1,1]*mean(grades(i,2:end)));
% For using the same color as the dots.
l.Color = h.CData;
end
%Titles to the plot
title('Grades per assignment');
xlabel('Assignment');
ylabel('Given grades');
axis([0 n_assignments+1 -4 13])
end
Remember that the break command must be used inside a loop, not for exiting a function. Use return if you desire.