how to plot points in different colors based on class?

   x1         x2     class
-1.7986   -1.6730     1
-1.0791   -0.5937     1
-0.5995    0.7556     1
1.0791   -1.4032      1
0.1199    0.2159      1
-0.3597   -0.4857    -1
0.3597   -1.5651     -1
-0.5995   -0.4857    -1
-0.1199    0.3238    -1
-1.5588   -0.4857    -1
how to plot x1 and x2 based on the class,class 1 and class -1 with different colors

Answer 1

[Image Analyst]

Try this:

clc;
m=[...
-1.7986   -1.6730     1
-1.0791   -0.5937     1
-0.5995    0.7556     1
1.0791   -1.4032      1
0.1199    0.2159      1
-0.3597   -0.4857    -1
0.3597   -1.5651     -1
-0.5995   -0.4857    -1
-0.1199    0.3238    -1
-1.5588   -0.4857    -1]
x1 = m(:,1);
x2 = m(:, 2);
classes = m(:,3);
sizes = 15 * ones(1,length(x1));
% Plot first class
scatter(x1(classes == 1), x2(classes == 1), 150, 'b', '*')
% Plot second class.
hold on;
scatter(x1(classes == -1), x2(classes == -1), 120, 'r', '*')

[Joseph Cheng]

on the same lines of scatter+hold on if you have more than 2 classes and it would be too tedious to code for each case the following can be used to plot in a for loop

x1 = rand(10,1);
x2= rand(10,1);
class = (-1).^randi(2,10,1).*randi(10,10,1);

uClass = unique(class)

pntColor = hsv(length(uClass))
figure,hold on
for ind = 1:length(uClass)
    scatter(x1(class == uClass(ind)), x2(class == uClass(ind)), 150, 'MarkerFaceColor',pntColor(ind,:),'Marker','*')
end

Answer 2

[Joseph Cheng]

you can find which indexes have either class and plot accordingly.

x1 = rand(10,1);
x2= rand(10,1);
class = (-1).^randi(2,10,1);

figure,plot(x1(class==1),x2(class==1),x1(class==-1),x2(class==-1))