Selecting required elements from a matrix

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arjun
arjun 2014-9-15
编辑： Guillaume 2014-9-15
I have a matrix A which contains 1's and 0's I wish to construct a new matrix B such that it has all the i,j values where A(i,j)=1, i.e B will be 2 X N matrix with its elements as the indices of the elements in matrix A who have a value of 1. for eg: A=[1,0,1,1,0] then B={[1,1];[1,3];[1,4]} Thanks
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Matt J
Matt J 2014-9-15
B={[1,1];[1,3];[1,4]} does not produce a 2xN matrix,
>> B={[1,1];[1,3];[1,4]}
B =
[1x2 double]
[1x2 double]
[1x2 double]

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Guillaume
Guillaume 2014-9-15
编辑：Guillaume 2014-9-15
Is this what you're after ?
[row, col] = find(A);
B = [row col]';
I.e. use the two output version of find.
edit: The above answer assumes A is not a row vector. You can use Matt J fix to handle all cases or, if you know that A is a row vector:
[row, col] = find(A);
B = [row; col];
  2 个评论
Matt J
Matt J 2014-9-15
Small fix, to handle the case when A is a row vector
B = [row(:) col(:)].';
Guillaume
Guillaume 2014-9-15
Oh yes, thanks!
I really hate that you can't write simple generic code in matlab because the shape of the output is not always the same.

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