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

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 ...

Answer 1

[Azzi Abdelmalek]

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

[SebLambert]

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 ?

[Azzi Abdelmalek]

It's true

Answer 2

[Youssef Khmou]

you can create your vectors as the following :

 C1=A(:,B(1));

 C2=A(:,B(2));

 C4=A(:,B(4));

[SebLambert]

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))