Extract element from column vector with condition

Question

Sagar Dhage 2014-8-8

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/146887-extract-element-from-column-vector-with-condition

评论： Sagar Dhage 2014-8-22

采纳的回答： Nir Rattner

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I have column vector

P=[ 0; 212; 111; 190; 0; 223; 123; 200; 189; 219; 0; 190; 175; 202; 167; 181

....and so on]

I want to extract the 2nd and 3rd elements from the left 0 element IF LENGTH BETWEEN TWO 0 (the left 0 and right 0) is GREATER THAN 3. Save 2nd position elements in P2 column vector and 3rd position elements in P3 column vector. The result should be

After extraction, the remaining elements should be placed into P1 such as

P1 = [ 0; 212; 111; 190; 0; 223; 189; 219; 0; 190; 167; 181 ....and so on]

P2 = [123; 175]
P3 = [200; 202]

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Sagar Dhage 2014-8-8

Oh sorry, extract 2nd and 3rd position element if IF LENGTH BETWEEN two 0 is GREATER THAN 3.

Image Analyst 2014-8-8

编辑：Image Analyst 2014-8-8

It might be clearer if you said "is 4 or more" rather than is "greater than 3". So the left run has 121, 111, 190 and that's 3, but not more than 3 (not 4 or greater) so those are left alone and get transferred to P1.

It's fairly easy if you have the Image Processing Toolbox. Do you?

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Answer 1

Nir Rattner 2014-8-8

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https://ww2.mathworks.cn/matlabcentral/answers/146887-extract-element-from-column-vector-with-condition#answer_147951

编辑：Nir Rattner 2014-8-8

在 MATLAB Online 中打开

You can use the “find” function to find the indices of your zeros and then subtract each index by the one before to make sure the distance between them is not too large.

P=[ 0;  212; 111; 190; 0;  223; 123; 200; 189; 219; 0; 190; 175; 202; 167; 181; 0;];
Pzeros = find(P == 0);
violators = Pzeros(find(Pzeros(2 : end) - Pzeros(1: end - 1) > 4));
P1 = P;
P1([violators + 2; violators + 3]) = [];
P2 = P(violators + 2);
P3 = P(violators + 3);

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Sagar Dhage 2014-8-8

Thank Nir...

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Answer 2

Azzi Abdelmalek 2014-8-8

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/146887-extract-element-from-column-vector-with-condition#answer_147946

编辑：Azzi Abdelmalek 2014-8-8

在 MATLAB Online 中打开

Edit

P=[ 0; 212; 111; 190; 0; 223; 123; 200; 189; 219; 0; 190; 175; 202; 167; 181 ]
ii=strfind(P'~=0,[0 1])
idx=ii([diff([ii numel(P)])]>4)
P1=P'
jj=[idx+2 idx+3]
P1(jj)=[]
P2=P(idx+2)'
P3=P(idx+3)'

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Sagar Dhage 2014-8-8

Thanks Azzi..its working..

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Answer 3

Image Analyst 2014-8-8

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https://ww2.mathworks.cn/matlabcentral/answers/146887-extract-element-from-column-vector-with-condition#answer_147950

在 MATLAB Online 中打开

Method using the Image Processing Toolbox:

P=[ 0; 212; 111; 190; 0; 223; 123; 200; 189; 219; 0; 190; 175; 202; 167; 181]
P2 = [];
P3 = [];
measurements = regionprops(P~=0, P, 'PixelValues', 'Area')
for k = 1 : length(measurements)
  % Show length of this stretch in the command window:
  fprintf('Area of stretch #%d = %d\n', k, measurements(k).Area);
  % Tack onto P2 and P3 if the length >= 4.
  if measurements(k).Area >= 4
    P2 = [P2, measurements(k).PixelValues(2)];
    P3 = [P3, measurements(k).PixelValues(3)];
  end
end
% Show in command window:
P2
P3

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Image Analyst 2014-8-12

I'm leaving on a week long trip in an hour. It looks like you've accepted an answer so then just go with that.

Sagar Dhage 2014-8-22

I have modified your programme.. nw its gives wat I want..Thank you.

% measurementsX = regionprops(Px~=0, Px, 'PixelValues', 'Area') % for k = 1 : length(measurementsX)

for k = 1 : length(measurementsX) % Show length of this stretch in the command window: %fprintf('Area of stretch #%d = %d\n', k, measurementsX(k).Area); % Tack onto P2 and P3 if the length >= 4. if measurementsX(k).Area == 1 P1X_1 = [P1X_1, measurementsX(k).PixelValues(1)]; end end

for k = 1 : length(measurementsX) % Show length of this stretch in the command window: %fprintf('Area of stretch #%d = %d\n', k, measurementsX(k).Area); % Tack onto P2 and P3 if the length >= 4. if measurementsX(k).Area == 3 P1X_3 = [P1X_3, measurementsX(k).PixelValues(1)]; P2X_3 = [P2X_3, measurementsX(k).PixelValues(2)]; P3X_3 = [P3X_3, measurementsX(k).PixelValues(3)]; end end

for k = 1 : length(measurementsX) % Show length of this stretch in the command window: %fprintf('Area of stretch #%d = %d\n', k, measurementsX(k).Area); % Tack onto P2 and P3 if the length >= 4. if measurementsX(k).Area ==5 P1X_5 = [P1X_5, measurementsX(k).PixelValues(1)]; P4X_5 = [P4X_5, measurementsX(k).PixelValues(2)]; P5X_5 = [P5X_5, measurementsX(k).PixelValues(3)]; P2X_5 = [P2X_5, measurementsX(k).PixelValues(4)]; P3X_5 = [P3X_5, measurementsX(k).PixelValues(5)]; end end

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