How do I index into a matrix with a vector to extract the jth column for each row?
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Richard
le 3 Mai 2016
Réponse apportée : Star Strider
le 3 Mai 2016
Is there an easy way to index into a matrix with a vector to extract the jth column of the matrix for each row? As an example, lets take the 4 x 4 matrix created by
A = magic(4);
A =
16 2 3 13
5 11 10 8
9 7 6 12
4 14 15 1
I have a vector which describes which columns I'd like to extract:
ii = [1; 2; 1; 2]
ii =
1
2
1
2
Is there a straightforward way of indexing into the matrix to return the vector:
result =
16
11
9
14
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Star Strider
le 3 Mai 2016
There is. Use the sub2ind function:
A = magic(4);
ii = [1; 2; 1; 2];
ix = sub2ind(size(A), [1:4]', ii);
result = A(ix)
result =
16
11
9
14
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