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I have a matrix [301,4201] and I would like to select only the values ​​ >=1.5.

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Alice Zaghini
Alice Zaghini on 24 Jun 2021
Commented: Steven Lord on 25 Jun 2021
However I don't know the position of the values inside the matrix. In the end I would always get a matrix (I don't know the final dimension).
  5 Comments
Steven Lord
Steven Lord on 25 Jun 2021
What if only 17 of the values in your matrix were greater than 1.5? What exactly would you want the shape of that submatrix to be? You have two choices in that case (assuming you don't want to add dimensions): it must be of size [1 17] or [17 1].
What if only 1000 of the values in your matrix were greater than 1.5? What shape would you want the submatrix to have?
Please explain in detail exactly what you want the submatrix to look like in those cases. That information may help us determine if what you want is possible in MATLAB and how to achieve it if it is.

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Answers (1)

Sean Brennan
Sean Brennan on 24 Jun 2021
This might help. The example below uses a random 10x10 matrix as a placeholder to demo the "find" command.
dummy_data = rand(10,10)*2; % Create a random 10x10 matrix where data is scattered between 0 and 2
% Find indices where data is larger than 1.5. These will range from 1 to
% 100 since there are 10x10 different elements, and MATLAB numbers them 1
% to 100 with 1,2,3 going down the first column, 11,12,13 down second
% column, etc. See ind2sub() to convert from MATLAB's internal indices to
% row,col form.
indices_big_number = find(dummy_data>1.5)
dummy_data(indices_big_number) % Show the results
% If you need the row and column, and don't like ind2sub, then use this
% [row_index,col_index] = find(dummy_data>1.5); % Find indices where data is larger than 1.5

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