# Is there such a matrix operation

Wolfgang2b
Say I have two matrices of the form

A = [1 0 0 1 0 1] (1 x 6 row vector)

and

B = [ a b c] (1 x 3 row vector). The number of elements in B = number of 1s in A.

Is there any matrix operation that could be done on A and B that would give me C = [a 0 0 b 0 c]? That is the 1's of A should be replaced with the values in B and zeros left as it is.

I am looking for operations that would not access the individual elements separately (i.e. I am not looking for things like if A(1)==1, C(1)=A(1)*b(1) etc... or inserting zeros.) I am looking for some operation like A*B that would give this result.

Sorry about the cryptic title. I can't really describe it without examples.

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## Answers and Replies

DonAntonio
Say I have two matrices of the form

A = [1 0 0 1 0 1]

Either this is a $\,1\times 6\,$ matrix, which is the same as a six-coordinate row vector, or you meant something else

that I, at least, cannot imagine what it is.

and

B = [ a b c]. The number of elements in B = number of 1s in A.

The same as above. Do you know what a matrix is? You should also know we have LaTeX in this site for us all to

properly write mathematics. This would be a huge improvement in this kind of question.

DonAntonio

Is there any matrix operation that could be done on A and B that would give me C = [a 0 0 b 0 c]? That is the 1's of A should be replaced with the values in B and zeros left as it is.

I am looking for operations that would not access the individual elements separately (i.e. I am not looking for things like if A(1)==1, C(1)=A(1)*b(1) etc... or inserting zeros.) I am looking for some operation like A*B that would give this result.

Sorry about the cryptic title. I can't really describe it without examples.

Wolfgang2b
Either this is a $\,1\times 6\,$ matrix, which is the same as a six-coordinate row vector, or you meant something else

that I, at least, cannot imagine what it is.

Yes, it is a 1 x 6 row vector or you can take the transpose and consider it a 6 x 1 column vector. Doesn't really matter. Same for the other matrix.

Do you know what a matrix is? You should also know we have LaTeX in this site for us all to

properly write mathematics. This would be a huge improvement in this kind of question.

DonAntonio
I know there was a matrix with Keanu Reeves in it. Like that one actually. I also have done few problems with the matrices in math. I don't know why this is relevant here. Can't I call row vectors as matrices? I store them as matrices in Matlab and would like to do matrix operations.

I also don't see the need to write this question in LaTeX as it does not contain any complex equations that would otherwise be unintelligible. However I would do that in future questions. For now, I will update the OP.