MATLAB: Extracting elements from a matrix according to row number

indexingmatrix

I need to extract the elements in each column of matrix A according to row numbers given by the elements of vector X. For example, I have:
A = 9 3 4 6
    2 4 5 7
    4 5 6 8
X = [1 3 1 2]
And I would like the indexing function to return this:
B = [9 5 4 7]
I tried B = A(X,1:end) but got an error saying "Subscript indices must either be real positive integers or logicals". Any help on this would be greatly appreciated as I am new to Matlab and can't figure out where I'm going wrong.

Best Answer

I would use the sub2ind function, to convert the subscripts to linear indices:
idx = sub2ind(size(A), X', (1:4)');
B = A(idx)
B =
     9
     5
     4
     7
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