Question

I’m plotting two vectors against one another. I would like to vary the symbol used to plot each point based on the corresponding value in a third vector.

In other words, if I’m plotting X and Y, I know I can make each plot point display as ‘*’ like so:

plot (X, Y, "*")

But how can I involve a third vector Z such that ‘*’ is displayed for some values of Z, and ‘+’ is displayed for others?

Answer 1

Try something like this:

x = [1 2 3];
y = [1 4 9];
z = {'*' '+' '*'};
for i_=1:length(x)
    eval(["plot(x(" num2str(i_) "),y(" num2str(i_) "),'" z{i_} "')"])
    hold on
end

This essentially makes n plots, where n is the length of x and y. If you want the point color to change for each point you can use hold all instead of hold on. If you want the point style to be conditional on the value of y, you can do

x = [1 2 3];
y = [1 4 9];
z = {'*' '+' '*'};
for i_=1:length(x)
    if (y(i_) > 1)
        z{i_} = '*';
    else
        z{i_} = '+';
    end
    eval(["plot(x(" num2str(i_) "),y(" num2str(i_) "),'" z{i_} "')"])
    hold on
end