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A question about sorting a vector

Asked by Cantor Set on 7 Sep 2019
Latest activity Commented on by Cantor Set on 8 Sep 2019
Suppose I have a column vector V of length N and I map every element in V to an element y in Y so, we have a column vector Y of length N.
Suppose I want to sort Y in an ascending order and pick r elements from the vector V that corrosponds to the least r values in Y.
I thought of:
V; Y;
N; r;
[Ys idx]=sort(Y);
for i=1:r
Best(i)=V(idx(Ys(i)))
end
Best(i)
So is this correct?

  2 Comments

That code gives an error for me. I assume it does for you, too. So, how can it be right?
Is this homework? You are pretty close to a solution, but
idx(Ys(i))
is the wrong way to index, because Ys(i) is not a whole number that can be used in this way.
A part of a homework problem.
Thank you!

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1 Answer

Answer by Star Strider
on 7 Sep 2019
 Accepted Answer

It does not look correct to me, specifically because ‘Ys’ may not necessarily be an integer greater than 0, as required for subscript references in MATLAB, and also within the size limits of ‘V’. (We have no idea what ‘Y’ is, since you have not told us.)
This may give you the result you want, however you have not told us that, either. It nevertheless avoids the explicit loop:
V = randn(10,1); % Create Vector
Y = randn(10,1); % Create Vector
[Ys, idx]=sort(Y);
r = 5; % Choose A Value
Best = V(idx(1:r)) % Result

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