How to give different colour for those indices which is zero in matlab plot

Hi All,

I am plotting numerical sensor data from huge file. I got my plot. But I want to show red colour to those points which is zero in the plot. I mean these data are wrong data and I want to give them different colur in the plot.

I tried with

idx=find(not(input5(:,1)));

But it will plot total zeros in the plot.How Can I rectify it. Thanks

Answer 1

[Image Analyst]

POKA, try this:

y = rand(1, 50) - 0.3;
x = 1 : length(y);
% clip some points to zero
y(y < 0) = 0;
% Find indexes above 0
aboveZero = y > 0;
% Plot all data.
plot(x, y, 'b*-', 'LineWidth', 2);
hold on;
grid on;
% Plot all data zero as red spots.
plot(x(~aboveZero), y(~aboveZero), 'r.', 'MarkerSize', 30);
xlabel('x', 'FontSize', 30);
ylabel('y', 'FontSize', 30);
title('Bad Data in Red', 'FontSize', 30);

[POKA]

Thanks .. I will try this

[POKA]

</matlabcentral/answers/uploaded_files/84167/jhakas.png> Hi Image Analyst It worked! Would you explain how you got those indices for which my data is zero. I could not understand ~abovezero part.

[POKA]

[Image Analyst]

From this:

aboveZero = y > 0;

you get a logical vector that is true if y is more than 0 and false if it's 0 or negative. So ~aboveZero is the opposite. It gives a logical vector that is false if y is more than 0 and true if it's 0 or negative.

So when do do y(~aboveZero) we get indexes only where ~aboveZero is true, in other words, only the indexes where y is zero or negative. Those are what I overplotted as red spots on top of all the original data.

[POKA]

Hi Image Analyst, I have one doubt . You made some points to zero and took indices for which data is not zero. But in my case I have already zeros in my data. So I doubt whether I am creating more zeros by executing previous lines.please see the data

[Image Analyst]

Ignore the first few lines where I had to create my own data because you initially forgot to attach yours:

y = rand(1, 50) - 0.3;
x = 1 : length(y);
% clip some points to zero
y(y < 0) = 0;

I had to have some data for the demo right? And I didn't have your data so I made up some. Since you already have the y data, you can just pick up with the line of code after those.

[POKA]

Thanks understood .

Answer 2

[David Goodmanson]

Hi POKA,

something like this?

x = 0:.01:50;
y = sin(x);
ind = abs(y)<.005   % or whatever tolerance is appropriate to find the zeros;
                    % sometimes y == 0 will not work
plot(x,y,x(ind),y(ind),'.r')