Use biplot(): How to plot three different colors after running PCA using only the first 2 principal components

Hello,

I am new to Matlab and I do not know the syntax well enough to do this task.

I have a data set and I split it into training and testing data as below:

X = csvread('mydata.csv');
flag = X(:,1);
label = X(:,2);
P = X(:,3:end);
train = X(flag < 5,:);
test = X(flag == 5,:);

Now for the "label", which is the second column of data set X, there are three different values: 0, 8, 9. I want to distinguish between the three classes (0, 8, 9) with a different plot symbol and color.

My research so far lets me believe that biplot() is the right tool in MATLAB to do this, but I am not sure how to what function to call or how to manipulate different parameters in biplot() to help me with this.

Below is what I have got so far:

Zeros = label(label == 0);
Eights = label(label == 8);
Nines = label(label == 9);
[coeff,score,latent] = pca(train);

plot (scores(Zeros), scores(Eights),scores(Nines),'.r','markersize', 20);
hold on
plot (scores(~Zeros), scores(~Eights),scores(~Nines),'^b', 'markersize', 7);
Subscript indices must either be real positive integers or logicals.

% Error in myPCA (line 24)
% plot (scores(Zeros), scores(Eights),scores(Nines),'.r','markersize', 20);

biplot(coeff(:,1:2),'scores',score(:,1:2));
% This works fine, but all of the data points are all red.

Thank you!