How to plot an array using a for loop?

Question

I want to plot inside a for loop. I tried the following code also used hold on but the plot is still blank. I don't know where I am getting wrong.

M2 = true(21, 6);
M2(1:2, 3:5) = false;

R = [0.5:0.1:2.5];
H=[0:5:25];
m=21,
n=6,
for i=1:m
    for j=1:n        
        if M(i,j)==0
            plot(H(i),R(j), 'color', 'r')
            drawnow();
        end
    end
end

try plot(H(i),R(j), 'r.'). You are plotting individual points. Plot expect lines. Unless you tell it that its a point to draw (the dot after red), it will try to draw a line, but a line with 1 point is invisible — Ander Biguri
– Ander Biguri, Commented Nov 24, 2020 at 11:46

saastn · Accepted Answer · 2020-11-24 13:25:25Z

1

As Ander Biguri already said, the plot function actually does not draw anything when you provide only one point and do not specify any markers.

But, if you want to create some animated plot, that one of the points is displayed at a time:

h = scatter(0, 0, 'r');
xlim([min(H) max(H)]);
ylim([min(R) max(R)]);
for i=1:m
    for j=1:n
        if M(i,j)==0
            set(h, 'xdata', H(i), 'ydata', R(j));
            pause(0.5);
            drawnow();
        end
    end
end

Or if you want to show all point together, you don't even need a loop:

[HH, RR] = meshgrid(H, R);
scatter(HH(~M), RR(~M), 'r');
xlim([min(H) max(H)]);
ylim([min(R) max(R)]);

edited Nov 24, 2020 at 13:25

answered Nov 24, 2020 at 13:19

saastn

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