access the elements in a matrix given the column indexes
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For example x = [1 2 3 4; 5 6 7 8; 9 10 11 12]
Given the row indexes vector y = [1 3 4]; I'd like to get the associated elements : x(1, y(1)) = 1, x(2, y(2)) = 7, x(3, y(3)) = 12. [1 7 12]
Don't use loop.
THanks
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Jan
2013-8-15
how about
diag( x(:, y) )
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Jan
2013-8-15
in x(:, y) the colon operator returns all rows of the matrix x. the second argument 'y' does 'column selection', i.e. it picks only the interesting columns from x:
x(:, [1 2 4])
ans =
1 2 4
5 6 8
9 10 12
the values you are looking for obviously appear as diagonal elements in the result and can be extracted with the diag() function.
the reason why the intersting values are on the diagonal is pretty simple, allthough I admit, that one might must give it a second thought :)
I hope that helped!
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