How to retrieve the location of the points plotted ordered

Question

Kevin Voogd 2020-6-2

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https://ww2.mathworks.cn/matlabcentral/answers/540531-how-to-retrieve-the-location-of-the-points-plotted-ordered

评论： Star Strider 2020-6-2

I have two vectors x and y which are not sorted. However, when I plot(x,y), it results in the expected plot. Here is an example of the arrays and the plot. As you can see, I would like to have the vectors ordered starting from x(1) = 0, y(1) = 0 and then following the order of the dots as if it was a continuous line. I cannot figure it out how to automatize this process since I have quite a lot arrays/graphs to look at and it is not worth it to do it manually.

x = [1.99802555286103e-05	2.11219844159594e-05	2.28345777469832e-05	2.39763066343323e-05	2.54034677435188e-05	2.59743321871934e-05	2.65451966308679e-05	2.74014932963798e-05	2.85432221837290e-05	2.85432221837290e-05	2.85432221837290e-05	2.85432221837290e-05	2.79723577400544e-05	2.76869255182171e-05	2.65451966308679e-05	2.54034677435188e-05	2.42617388561696e-05	2.28345777469832e-05	2.11219844159594e-05	1.91239588630984e-05	1.71259333102374e-05	1.59842044228882e-05	1.39861788700272e-05	1.19881533171662e-05	9.70469554246784e-06	7.42123776776952e-06	5.70864443674578e-06	3.99605110572207e-06	1.99802555286102e-06	0];
y = [-3.68207566170104e-05	-3.48227310641493e-05	-3.33955699549629e-05	-3.13975444021019e-05	-2.96849510710781e-05	-2.74014932963798e-05	-2.54034677435188e-05	-2.34054421906578e-05	-2.11219844159595e-05	-1.88385266412611e-05	-1.62696366447255e-05	-1.39861788700272e-05	-1.11318566516543e-05	-9.13383109879327e-06	-7.99210221144412e-06	-6.27950888042038e-06	-5.13777999307122e-06	-3.71061888388478e-06	-3.13975444021020e-06	-3.13975444021020e-06	-2.85432221837291e-06	-2.85432221837291e-06	-2.56888999653562e-06	-2.56888999653562e-06	-2.56888999653562e-06	-2.28345777469833e-06	-2.28345777469833e-06	-1.99802555286104e-06	-1.42716110918645e-06	0];

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Answer 1

Star Strider 2020-6-2

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https://ww2.mathworks.cn/matlabcentral/answers/540531-how-to-retrieve-the-location-of-the-points-plotted-ordered#answer_444979

在 MATLAB Online 中打开

The easiest way to do that is to use the flip function (or fliplr or flipud, depending on what you want to do).

Try this:

flipx = flip(x);
flipy = flip(y);
figure
plot(flipx, flipy)
grid
dx = gradient(flipx);                           % Optional
dy = gradient(flipy);                           % Optional
figure                                          % Optional
quiver(flipx, flipy, dx,dy)                     % Optional
grid

The quiver plot just demonstrates that the flip operation does what you want it to do. It is not necesary for the code.

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Kevin Voogd 2020-6-2

Dear Star Strider,

indeed the flip function is what I was looking for. You saved me!

Thank you!

Star Strider 2020-6-2

As always, my pleasure!

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Answer 2

Fangjun Jiang 2020-6-2

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https://ww2.mathworks.cn/matlabcentral/answers/540531-how-to-retrieve-the-location-of-the-points-plotted-ordered#answer_444967

编辑：Fangjun Jiang 2020-6-2

在 MATLAB Online 中打开

If you run plot(x,y) instead of plot(x,y,'o'), you will see the correct curve. So your data is already "sorted" as you wanted. I would say that you are lucky that the x, y data is in current order. If x is sorted based on its value, it would be hard to get to the current order.

To illustrate the issue

% x data is in the right order, both curve and dot plot are correct
figure;plot(x,y,'o');
figure;plot(x,y);
% x data is sorted by value, curve plot is incorrect
[xx,index]=sort(x);
yy=y(index);
figure;plot(xx,yy,'*');
figure;plot(xx,yy);

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Kevin Voogd 2020-6-2

Dear Fangjun Jiang, thank you for your time. However, the answer that Star Strider wrote is what I was looking for. I am sorry if my question was not clear enough.

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