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How to extract matrix from a bigger matrix based on threshold of each column?

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I have a nX3 matrix. I need to extract a matrix such that all rows crossing the threshold of each column are selected. Threshold can be assumed to be 100(column 1),200(column2) and 300(column 3 )? Please help...

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Accepted Answer

Philippe Lebel
Philippe Lebel on 2 Dec 2019
Edited: Philippe Lebel on 2 Dec 2019
here is my try based on what i understood.
given a matrix a nx3:
a = [5,6,8;1,2,3;2,3,4;3,4,5;4,5,6]
a =
5 6 8
1 2 3
2 3 4
3 4 5
4 5 6
% the threshold on column 1 is 2
a_1 = a(a(:,1)>2,:)
a_1 =
5 6 8
3 4 5
4 5 6
% the treshold on column 2 is 4
a_2 = a_1(a_1(:,2)>4,:)
a_2 =
5 6 8
4 5 6
%the treshold on column 3 is 6
a_3 = a_2(a_2(:,3)>6,:)
a_3 =
5 6 8
a_3 is the matrix containing the row(s) that satisfy all tresholds.
A one-liner can be made for this operation:
a_tresh = a((a(:,1)>2)&(a(:,2)>4)&(a(:,3)>6),:)
a_tresh =
5 6 8

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Adam Danz
Adam Danz on 2 Dec 2019
This can be simplified and reduced to
a = [5,6,8;1,2,3;2,3,4;3,4,5;4,5,6];
thresh = [2,4,6]; % Row vector defining the threshold of each column of 'a'
a(all(a > thresh,2),:)
% ans =
% 5 6 8
Adam Danz
Adam Danz on 2 Dec 2019
Nice job interpreting the question. I wouldn't have guessed. Too many times I guessed on other questions, spent time writing out the solution, and then found that my interpretation wasn't correct.

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