How to replace zeros in a matrix by the elements of an array?

Question

Julius 2012-6-6

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Hi everybody! I have a matrix (A) that contains zeros but it may contain also ones.

    R=1:8;     A=[1 0 0 0;
                  0 0 0 0; 
                  1 0 1 1]

How to replace all the ones by zeros and all the zeros by elements of an array (R) going column-wise so that the resulting matrix (B) would look like:

               B=[0 2 5 7;
                  1 3 6 8;
                  0 4 0 0]

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Thomas 2012-6-6

I think this might be homework.. can you show what you have done so far?

Julius 2012-6-6

Yes, I've done this:

D=3;

N=4;

A=zeros(D,N);

equations=sum(A(:)==0);

R=1:equations;

for j=1:N

for i=1:D

if A(i,j)==1

A(i,j)=0;

else

ID(i,j)=?????;

end

B=A

....but I don't know how to continue

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Answer 1

Thomas 2012-6-6

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在 MATLAB Online 中打开

You are on the right track, though it can be done in much simpler way but since you are a beginner this will suffice..

use

Your input matrix was zeros, just add a count for R values

Editing your code:

A=[1 0 0 0;
                  0 0 0 0; 
                  1 0 1 1]  
D=3;
N=4;
% A=zeros(D,N);
equations=sum(A(:)==0);
R=1:equations;
count=1;
for j=1:N
for i=1:D
if A(i,j)==1
A(i,j)=0;
else
ID(i,j)=R(count);
count=count+1;
end
end
end 
ID

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Thomas 2012-6-6

count is a variable.. I'm incrementing it every iteration..

Julius 2012-6-6

I see.....that's why I didn't find such command. Very clever!

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Answer 2

Image Analyst 2012-6-6

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https://ww2.mathworks.cn/matlabcentral/answers/40461-how-to-replace-zeros-in-a-matrix-by-the-elements-of-an-array#answer_50113

在 MATLAB Online 中打开

R=1:8;    
A=[1 0 0 0;
   0 0 0 0; 
   1 0 1 1]
linearIndices = A == 0
B = A; % Make a copy.
B(A==1) = 0
B(linearIndices) = R;

This is a vectorized way of doing it rather than your for loop method.

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Julius 2012-6-6

I just wanted to write down that the answer for your question is: B(A==0)=R.Meanwhile, you have done it instead of me. I just tried it and it worked. It wouldn't even cross my mind to do it that way. And it seems to be a faster code than the mine one. Thank you!

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