Sort and Compare elements in a row matrix to form a new one

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Konstantinos 2015-2-6

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评论： Konstantinos 2015-2-6

采纳的回答： Guillaume

I have the following row matrix (1x8):

Α = [ 1 0 0 1 0.5 0.4 0.5 0.4 ]

and I want to create a new matrix Β which contains the 5 elements of A with the higher values in a descending order:

Β = [ 1 1 0.5 0.5 0.4 ]

In the current example, A(6)=A(8)=0.4, so in this case I want to randomly choose which of these 2 elements will continue to form B and not neccesary take the one with the smaller index number (i.e A(6) instead of A(8)). If we assume that we don't know the elements of matrix A then we have to sort them and compare them before we form B. Can anyone share with me the appropriate code ?

Any help could be useful. Thanks in advance!

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Guillaume 2015-2-6

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I don't understand that bit: A(6)=A(8)=0.4, so in this case I want to randomly choose which of these 2 elements will continue to form B. Since they are the same value, chosing one at random or not does not matter, you always get the same value.

A = [1 0 0 1 0.5 0.4 0.5 0.4];
B = sort(A, 'descend');
B = B(1:5)

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Guillaume 2015-2-6

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Here is one way:

A = [1 0 0 1 0.5 0.4 0.5 0.4 0.3 0.4 0.2 0.4];
[B, idx] = sort(A, 'descend');  %sort in descending order as normal
lastindices = idx(B == B(5));   %get indices for element equals to B(5)
idx(B == B(5)) = lastindices(randperm(numel(lastindices))); %and shuffle randomly
B = B(1:5)
idx = idx(1:5)