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how to change every value not equal to X in every rows

Asked by Isabelle Bouret on 17 Apr 2019
Latest activity Commented on by Walter Roberson
on 17 Apr 2019
Hi,
I have a matrix (20000x365) and I have a vector(20000x1) in which I have the column assiciate with the number that I DON'T want to change (This number change for every rows) .
For every rows I want to change every colums, beside the one that is in the vector, for 0
EX: matrix [18 3 1 11; 8 10 11 3; 9 14 6 1; 4 3 15 21]
Vector [3,1,3,2]
The answers should be [0 0 1 0; 8 0 0 0; 0 0 6 0; 0 3 0 0]
Thanks for your help!

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2 Answers

Answer by madhan ravi
on 17 Apr 2019
Edited by madhan ravi
on 17 Apr 2019
 Accepted Answer

Wanted = zeros(size(matrix));
indices=sub2ind(size(matrix),1:size(matrix,1),Vector);
Wanted(indices)=matrix(indices)

  6 Comments

See edited answer. size(matrix,1) not 2 also Vector.' - transpose Vector
indices=sub2ind(size(matrix),1:size(matrix,1),Vector.')
% it's easy to figure it out isn't ?
1:size(matrix,1) % creates a row vector
Vector.' % so if Vector is a column vector transpose it to create a row vector
Thank you!!
I have to modified a llittle bit
Wanted = zeros(size(l_s));
for i=1:L
if Vector(i,:)==0
continue
else
indices=sub2ind(size(Matrice),i,Vector(i,:).');
Wanted(indices)=Matrice(indices);
end
end
This work perfectly event though it may not be efficient
If you are going to loop then
Wanted = zeros(size(l_s));
for i = 1:L
if Vector(i) ~= 0
Wanted(i, Vector(i)) = Matrice(i, Vector(i));
end
end
or
Wanted = zeros(size(l_s));
for i = find(Vector)
Wanted(i, Vector(i)) = Matrice(i, Vector(i));
end

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Answer by Walter Roberson
on 17 Apr 2019
Edited by Walter Roberson
on 17 Apr 2019

rows = size(EX_matrix,1);
ind = (1:rows).' + (Vector(:)-1)*rows;
Output = zeros(size(EX_matrix));
Output(ind) = EX_matrix(ind);

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