How to plot one curve and change color according to value

Question

Manitux 2024-8-18，18:03

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https://ww2.mathworks.cn/matlabcentral/answers/2146114-how-to-plot-one-curve-and-change-color-according-to-value

评论： Manitux 2024-8-19，19:07

The tricky thing is that I get an attribute with the values and would like to have this part in the plot in a different color:

x = linspace(0,10);

y = sin(3*x).*exp(0.5*x);

c = find(y > 25);

m(length(x)) = 0;

m(c) = 1;

figure;

plot(x, y, 'b')

Where m becomes 1 the color should be red, else blue.

Can someone find the easiest way to do this?

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Manitux 2024-8-18，19:50

Ah, I see there is a misunderstanding. The "m" is part of the transmitted data, not a special limit. For the demo-code it was just generated as an example.

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Answer 1

DGM 2024-8-18，19:39

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Also:

% inputs

thresh = 25;

x = linspace(0,10,100);

y = sin(3*x).*exp(0.5*x);

% m is equivalent to (y>thresh), so it's entirely redundant

% adding 1 here casts the logical result to float

% and converts it to a 1-based index vector for direct

% addressing of the color table (CT)

c = (y > thresh) + 1;

% create an unfilled patch

hp = patch([x NaN],[y NaN],[c NaN],'EdgeColor','interp');

hp.LineWidth = 2; % if you want fatter lines

yline(thresh);

% apply the color

CT = [0 0 1; 1 0 0];

colormap(CT)

Of course, the color transitions where ever there are samples in the data, not necessarily exactly on y=25.

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Image Analyst 2024-8-19，15:22

编辑：Image Analyst 2024-8-19，15:23

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I don't understand why we need both m and c and c0. Isn't it just y > 25, like

m = y > 25

Manitux 2024-8-19，19:07

Try this:

x = linspace(0,10);

y = randi([-50 50], 1, length(x));

m(length(x)) = 0;

m([30 31 32 33 34 35 36 37 60 61 62 63 64 65 90 91 92 93 94 95]) = 1;

patch([x NaN],[y NaN],[m NaN],'EdgeColor','interp');

CT = [0 0 1; 1 0 0];

colormap(CT)

"y" and "m" are signals I receive on an interface and need to paint "y" in 2 different colors, depending on the bool of "m". My first sample was just how I tried to get this solved (by myself).

But your idea to take "patch" is brilliant ;-)

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Answer 2

Image Analyst 2024-8-18，18:34

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Maybe this:

x = linspace(0,10);

y = sin(3*x) .* exp(0.5 * x);

plot(x,y,'-b.');

hold on

yline(25, 'LineWidth', 2, 'Color', 'm');

mask = y > 25;

y1 = nan(1, numel(y));

y1(mask) = y(mask);

plot(x, y1,'-r.');

grid on;

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William Rose 2024-8-18，19:39

@Image Analyst, nice.

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Answer 3

John D'Errico 2024-8-18，22:07

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编辑：John D'Errico 2024-8-18，22:12

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As ifs often the case, I am far too late to the party. :) But there are often many ways to solve a problem, so I like to be able to offer an alternative. scatter is one in this case.

x = 1:100;

y = sin(x/10);

scatter(x,y,[],y > 0.5)

yline(0.5,'r')

For more complex cases, scatter can still work. And, of course, we can control the colormap used.

k = cos(x/10) > 0;

scatter(x,y,[],k)

colormap([0 1 0;0 0 1])

And finally, scatter will alllow me to segregate multiple sections on the curve, according to my choosing.

k = round(cos(x/10));

scatter(x,y,[],k)

colormap([1 0 0;0 1 0;0 0 1])