CODEWITHSUNDEEP
octave
jdmcnair
jdmcnair

Reputation: 1315

Octave - Variable point symbol in plot

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?

Upvotes: 2

Views: 3866

Answers (3)

TheCommonEngineer
TheCommonEngineer

Reputation: 527

Can also be done by getting the indices of elements of Z for which +/* are to printed in 2 separate arrays using find method.

Considering that you want to print (+) for positive values of Z and (*) for negative values, the following code will do it:

    pos = find(Z > 0); neg = find(Z <= 0);
    plot(X(pos), Y(pos), 'k+', X(neg), Y(neg), 'k*');

Upvotes: 4

Bill Yang
Bill Yang

Reputation: 1413

code below will print 'ro' for z > 0 and 'bx' for z < 0

plot(x(z>0), y(z>0), 'ro', x(z<0), y(z<0), 'bx')

Upvotes: 2

andyras
andyras

Reputation: 15930

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

Upvotes: 2

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