# Finding a value of one vector based on the nonzero values of another vector

2 views (last 30 days)
L'O.G. on 8 Dec 2022
Commented: Stephen23 on 8 Dec 2022
Given two vectors, how do you determine the value of A where B is 1? In this case, A=[5 4]. How do I do this?
A = [2 5 1 4];
B = [0 1 0 1];

Arif Hoq on 8 Dec 2022
Edited: Arif Hoq on 8 Dec 2022
A = [2 5 1 4];
B = [0 1 0 1];
[I C]=find(B==1);
output=A(C)
output = 1×2
5 4

Image Analyst on 8 Dec 2022
If B is always guaranteed to be 0 or 1, you can do this
A = [2 5 1 4];
B = [0 1 0 1]; % B is a double here.
A = A(logical(B)) % Need to cast B to logical
A = 1×2
5 4
If B can be anything and you want to get A where B is not equal to zero:
A = [2 5 1 4];
B = [0 23 0 341];
A = A(B ~= 0)
A = 1×2
5 4
Stephen23 on 8 Dec 2022
Using LOGICAL() works in both cases:
A = [2 5 1 4];
B = [0 23 0 341];
A = A(logical(B))
A = 1×2
5 4

Voss on 8 Dec 2022
A = A(B == 1)

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