How to plot one curve and change color according to value

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Manitux
Manitux 2024-8-18
评论： Manitux 2024-8-19
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?
  1 个评论
Manitux
Manitux 2024-8-18
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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采纳的回答

DGM
DGM 2024-8-18
Ran in:
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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显示 3更早的评论
Image Analyst
Image Analyst 2024-8-19
编辑：Image Analyst 2024-8-19
I don't understand why we need both m and c and c0. Isn't it just y > 25, like
m = y > 25
Manitux
Manitux 2024-8-19
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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更多回答（3 个）

Image Analyst
Image Analyst 2024-8-18
Ran in:
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;
John D'Errico
John D'Errico 2024-8-18
编辑：John D'Errico 2024-8-18
Ran in:
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])
colorbar
William Rose
William Rose 2024-8-18
编辑：William Rose 2024-8-18
Ran in:
@Fritz Weld,
[Edit: clean up code a lttle bit.]
x = linspace(0,10);
y = sin(3*x).*exp(0.5*x);
y1=zeros(size(y)); y2=y1; % initialize
for i=1:length(y)
if y(i)<=25
y1(i)=y(i);
y2(i)=NaN;
else
y1(i)=NaN;
y2(i)=y(i);
end
end
plot(x,y1,'-b.',x,y2,'-r.');
Probably not the easiest or prettiest way to do it but it works.
Another approach is to use scatter with a colormap.
  1 个评论
William Rose
William Rose 2024-8-18
Ran in:
@Fritz Weld,
x = linspace(0,10);
y = sin(3*x).*exp(0.5*x);
c=(y>25);
map=[0,0,1;1,0,0];
scatter(x,y,[],c,'filled');
colormap(gca,map);
"scatter" will not connect the points.

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