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

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...

[Adam Danz]

Small examples of inputs and expected outputs are usually worth 1000 words.

Answer 1

[Philippe Lebel]

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

[Mathieu Morel]

Thanks a lot !

[Adam Danz]

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

[Philippe Lebel]

nice one, I forgot about all()

thanks for the input

[Adam Danz]

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.