How to extract a part of a matrix with condition in Matlab

Question

I have a sat of matrices and I want to extract only a part of the matrix that satisfy a condition.

For example: values of the 150x180 matrix goes from 0 to 2.80 and I only want those between 1.66 and 1.77 I want to keep the values within the rang in their original location in the original matrix and set the other to zero.

can anybody help me please.

Thank you

Answer 1

You can use logical indexing. First, find A entries that do not satisfy your conditions. Next, using A(idx) change them to 0:

% example matrix
A = 2.8*rand(150, 180);

% find entries meeting some criterion
idx = A<1.66 | A>1.77;
A(idx) = 0;

Or simpler, as Rody Oldenhuis suggested, you can include the logical expression directly in the matrix reference:

A(A<1.66 | A>1.77) = 0;

This yields a shorter and cleaner code, but not a faster code: MATLAB still explicitly creates the logical index variable, but clears it afterwards.