how to do something like A(:,B(:)) ?

2013 9 25
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Hello everybody,
I have a matrix A of size n x p, e.g. 10*4
A =
0.2760 0.7513 0.8407 0.3517
0.6797 0.2551 0.2543 0.8308
0.6551 0.5060 0.8143 0.5853
0.1626 0.6991 0.2435 0.5497
0.1190 0.8909 0.9293 0.9172
0.4984 0.9593 0.3500 0.2858
0.9597 0.5472 0.1966 0.7572
0.3404 0.1386 0.2511 0.7537
0.5853 0.1493 0.6160 0.3804
0.2238 0.2575 0.4733 0.5678
and a vector B (1 x n), e.g.
B =
2 2 4 4 1 2 2 3 3 4
and I would like to build a vector C (1 x n) where C(k) = A(k,B(k)) (in my example I would like to get C = [0.7513 0.2551 0.5853 .......] I thought I was pretty comfortable with matlab syntax but I'm lost there ! :) if anyone has any idea ...

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Azzi Abdelmalek
Azzi Abdelmalek 2013-9-25

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nm=size(A)
C=A(sub2ind(nm,1:nm(1),B))

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SebLambert
SebLambert 2013-9-25
ok thank you very much ! that is where I was arriving myself :) but then if A is n x p x q and B is n x p, I have to do something like :
[X,Y] = ndgrid(1:size(A,1),1:size(A,2));
A(sub2ind(size(A),X,Y,B))
Am I right ?

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Youssef Khmou
Youssef Khmou 2013-9-25

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you can create your vectors as the following :
C1=A(:,B(1));
C2=A(:,B(2));
C4=A(:,B(4));

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SebLambert
SebLambert 2013-9-25
thanks for your answer but I guess that is not what I want to do :) I want to have only one vector where the kth element is A(k,B(k))

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