Find a position of last changing value in array

Question

Nik Rocky 2020-6-7

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https://ww2.mathworks.cn/matlabcentral/answers/543983-find-a-position-of-last-changing-value-in-array

评论： Nik Rocky 2020-6-7

Hello,

i'm looking for function that detect a position of detection of last changing value (value stay constant or have just little changes).

In this case tube_dimension = 37;

I'm realize this in for-loop, but maybe thereare better way?

Sensivity_old = Sensivity;
TP ...
FN ....
Sensivity = (TP ./ (TP + FN));
if (Sensivity > Sensivity_old + 1.0e-03)
   Sencivity_end = tube_cnt;
else   
end
disp(Sencivity_end)

Thank you!

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Answer 1

Umair Hassan 2020-6-7

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https://ww2.mathworks.cn/matlabcentral/answers/543983-find-a-position-of-last-changing-value-in-array#answer_447677

编辑：Umair Hassan 2020-6-7

在 MATLAB Online 中打开

Hi Nikita,

You can use MATLAB's built in function differentrial (diff) to find out the minimum variability points of your data. The first index of the those points would be where your data would have the plateau. If you can attach some data, I would give you a code as well, otherwise psuedo code is:

plateau_points=diff(sensitivity);
plateau_points=find(plateau_points ==0) % finding where the points have 0 change
plateau_tube_dimension=tube_dimension(plateau_points(1));

Hope this helps,

Thanks!

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Nik Rocky 2020-6-7

在 MATLAB Online 中打开

Hi Hassan,

thanks for your response!

I trieded to do your Answer:

My input is:

Sensivity =
  Columns 1 through 18
    0.8749    0.8806    0.8860    0.9100    0.9114    0.9130    0.9361    0.9374    0.9480    0.9493    0.9539    0.9559    0.9576    0.9586    0.9596    0.9606    0.9609    0.9612
  Columns 19 through 36
    0.9619    0.9622    0.9626    0.9632    0.9639    0.9649    0.9659    0.9665    0.9672    0.9675    0.9675    0.9679    0.9682    0.9685    0.9685    0.9712    0.9728    0.9745
  Columns 37 through 50
    0.9768    0.9771    0.9771    0.9771    0.9771    0.9771    0.9771    0.9771    0.9771    0.9771    0.9771    0.9771    0.9771    0.9771

after

plateau_points=diff(Sensivity)

I get:

plateau_points =
  Columns 1 through 18
    0.0057    0.0054    0.0241    0.0013    0.0017    0.0231    0.0012    0.0106    0.0013    0.0046    0.0020    0.0017    0.0010    0.0010    0.0010    0.0003    0.0003    0.0007
  Columns 19 through 36
    0.0003    0.0003    0.0007    0.0007    0.0010    0.0010    0.0007    0.0007    0.0003         0    0.0003    0.0003    0.0003         0    0.0027    0.0017    0.0017    0.0023
  Columns 37 through 49
    0.0003         0         0         0         0         0         0         0         0         0         0         0         0

after:

plateau_points=diff(Sensivity);
plateau_points=find(plateau_points > 0); % finding where the points have 0 change
plateau_tube_dimension = nonzeros(plateau_points(end));

I get 37! Is a right one. Thank you very much!

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