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How to replace elements in a matrix using logical

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Ara Jo on 19 Oct 2020
Closed: MATLAB Answer Bot on 20 Aug 2021
Hello,
I would like to set some columns to zero for certain rows indicated by a logical. For instance, if we have a matrix X
X =
1 1 1 1
2 2 2 2
3 3 3 3
4 4 4 4
Suppose I have a logical that is true for row 3 and 4. Then I would like to replace column 3 to 4 with zero for row 3 and 4, so that the result is:
X =
1 1 1 1
2 2 2 2
3 3 0 0
4 4 0 0
To indicate the columns I want to replace I have tried things like 3:end, or size(B,1):end, but I get a message Subscript indices must either be real positive integers or logicals.
However, even if I only use integers, let's say 3:4, I still get the same message. What am I doing wrong? Thanks for your advice!

Ameer Hamza on 19 Oct 2020
Edited: Ameer Hamza on 19 Oct 2020
Try this
X = [
1 1 1 1
2 2 2 2
3 3 3 3
4 4 4 4];
tf = [false; false; true; true];
X(tf, tf) = 0;
Result
>> X
X =
1 1 1 1
2 2 2 2
3 3 0 0
4 4 0 0