Extract top 10 values from each row

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Saurabh
Saurabh 2011-10-10
Hello,
I have a matrix and wish to keep only the top 10 values in each row and replace all the other (bottom 90) values with zeros. Is there an efficient way to achieve this?

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采纳的回答

Walter Roberson
Walter Roberson 2011-10-10
[sortvals, sortidx] = sort(A,'descend');
B = zeros(size(A),class(A));
for K = 1 : size(A,2)
B(sortidx(1:10,K),K) = sortvals(1:10,K);
end
Yes, it could probably be done without a loop, using sub2ind(), but that would not necessarily be any faster, and would probably be less clear.
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Walter Roberson
Walter Roberson 2011-10-10
Adjusting for rows:
[sortvals, sortidx] = sort(A,2,'descend');
B = zeros(size(A),class(A));
for K = 1 : size(A,1)
B(K,sortidx(K,1:10)) = sortvals(K,1:10);
end

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更多回答（1 个）

Laura Proctor
Laura Proctor 2011-10-10
This code will keep the top ten rows and replaces everything from the 11th row on with a zero.
A = rand(100);
A(11:end,:) = 0;
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Saurabh
Saurabh 2011-10-10
Oh, I meant 'top 10' as in the maximum 10 values.
Example, for simplicity, consider the top 2 values
A =
1 2 3 4
4 3 2 5
6 5 4 2
1 4 2 3
Then I want the output as
B =
0 0 3 4
4 0 0 5
6 5 4 2
0 4 0 3
Thus, the top two values of each row are kept and others are replaced with zeros.
Saurabh
Saurabh 2011-10-10
I answered a bit late.
Laura: That method would work, but it destroys the element order. I wish to preserve the order as in above example.

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