Adding a random value (-0.1 : 0.1) to scatterplot data points to prevent exact overlapping.

Hello.

Ive been tasked with generating a scatterplot for grading students' assignments. The variable 'grades' is loaded from a .csv file, which ill be attaching to this post.

I've managed to make the loop work, generating the proper scatterplot, but I am supposed to apply a random value between -0.1 : 0.1 to the datapoints, IF there are multiple plotted in the same spot. The random value in this interval MUST be added to both the x- and y-value for each datapoint that overlaps. I simply do not know how to do that.

grades = readtable(grades);
G = zeros(height(grades), width(grades)-2);
for i = 3 : width(grades)
    G(:,(-2+i)) = table2array(grades(:,i));
end

AS = [1: size(G,2)];

figure()
hold on
for i = 1 : size(G,1)
    Gd = zeros(1, size(G,1));
    Gd = G(i,:);
    scatter(AS, Gd);
end
xlim([0 size(grades,2)-1]), xticks([1:1:size(grades,2)-2]), 
ylim([-5 14]), yticks(Scale),
title('Students grading on assignments'), xlabel('Assignment'),
ylabel('Grade');
hold off

Is there any way to quickly and/or easily implement that change in my code? The attached code is part of a function script (more specifically, the 2nd section of the script). In case it is needed in order to assist me, the full script is attached as well.

function gradesPlot(grades)
close all

Scale = [-3 0 2 4 7 10 12];
G = computeFinalGrades(grades);
A = [sum(G(:) == -3) sum(G(:) == 0) sum(G(:) == 2) sum(G(:) == 4) ...
    sum(G(:) == 7) sum(G(:) == 10) sum(G(:) == 12)];

figure()
hold on
bar(Scale, A);
ylim([0 max(A)+1]), yticks(0:1:max(A)+1), xlim([-5 14]),  
xticks(Scale), title('Students grading'), xlabel('Grade'),
ylabel('Amount of students');
hold off

% -------------------------------------------------------------------------

grades = readtable(grades);
G = zeros(height(grades), width(grades)-2);
for i = 3 : width(grades)
    G(:,(-2+i)) = table2array(grades(:,i));
end

AS = [1: size(G,2)];

figure()
hold on
for i = 1 : size(G,1)
    Gd = zeros(1, size(G,1));
    Gd = G(i,:);
    scatter(AS, Gd);
end
xlim([0 size(grades,2)-1]), xticks([1:1:size(grades,2)-2]), 
ylim([-5 14]), yticks(Scale),
title('Students grading on assignments'), xlabel('Assignment'),
ylabel('Grade');
hold off

% -------------------------------------------------------------------------

Gm = zeros(1, size(G,2));
for i = 1 : size(G,2)
    Gm(:,i) = mean(G(:,i));
end

figure()
hold on
plot(AS,Gm)
xlim([0 size(grades,2)-1]), xticks([1:1:size(grades,2)-2]), 
ylim([-5 14]), yticks(Scale),
title('Average grading on assignments'), xlabel('Assignment'),
ylabel('Average grade');
hold off

Answer 1

[OCDER]

Try this example to see how to adjust X and Y values by a random value between -0.1 to 0.1 only if (x,y) are duplicates.

X = [1 1 2 2 3 3 4 4]';
Y = [1 1 3 4 5 5 6 7]'; %(x,y) = (1,1) and (3,5) have overlapping points
Xadj = zeros(size(X));  %store values to adjust x
Yadj = zeros(size(Y));  %store values to adjust y
[~, ~, Idx] = unique([X Y], 'rows');  %find unique (x,y) coordinates
for j = 1:length(Idx)
    Loc = (Idx == j);
    Copies = sum(Loc);
    if Copies > 1
        Xadj(Loc) = 0.2*rand(Copies, 1) - 0.1; %add values from -0.1 to 0.1
        Yadj(Loc) = 0.2*rand(Copies, 1) - 0.1; %add values from -0.1 to 0.1
    end
end
scatter(X+Xadj, Y+Yadj) %Plot X and Y, adjusting values if they overlap.

%NOTE: Adjustment could still be too small that overlaps happen. 
       You would need to set a minimum adjustment value then.