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Could anyone help me how to display the top three highest values in each column and display the other values to be zero.

Asked by jaah navi on 2 Jun 2019
Latest activity Edited by Guillaume
on 2 Jun 2019
I am having a matrix
A= [2.3433 2.8950 2.9967 3.8753 3.9190 3.9104 3.9563 3.9525;
0.5167 0.4839 0.4885 0.1197 0.2249 0.2497 0.2874 0.2798;
0.4429 0.4348 0.4009 0.2255 0.1793 0.2188 0.1807 0.1816;
0.3900 0.1836 0.1741 0.1292 0.1241 0.1093 0.1058 0.1280;
0.0792 0.1701 0.1765 0.1033 0.0859 0.0758 0.0681 0.0769;
0.2301 0.1068 0.1036 0.0698 0.0868 0.0945 0.0912 0.0847]
I want to display the top three highest values in each column and the rest of the other values should be displayed as zero.
Could anyone please help me on this.

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2 Answers

Answer by Guillaume
on 2 Jun 2019
 Accepted Answer

Getting the top 3 values of each column is trivial with maxk
top3 = maxk(A, 3, 1)
I don't see the point in having 0s below these values but if that's you really want, you can simply concatenate a zero matrix below that
top3padded = [mask(A, 3, 1); zeros(size(A, 1)-3, size(A, 2))]

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When i use the above command its staing undefined function or variable maxk,mask.
For your info if
A=[0.5238 0.9547 0.7060 0.3709 0.9102 0.9044 0.1877 0.2748;
0.2649 0.4306 0.6451 0.8909 0.9091 0.0332 0.3219 0.2415;
0.0684 0.9616 0.5523 0.8564 0.5916 0.5324 0.4039 0.2431;
0.4363 0.7624 0.2181 0.4024 0.3326 0.7165 0.5486 0.1542;
0.1739 0.0073 0.7724 0.3180 0.8531 0.1793 0.0487 0.9564;
0.0261 0.6800 0.2280 0.6086 0.4424 0.3365 0.5527 0.9357]
i need to have
B=[0.5238 0.9547 0.7060 0 0.9102 0.9044 0 0.2748;
0.2649 0 0.6451 0.8909 0.9091 0 0 0 ;
0 0.9616 0 0.8564 0 0.5324 0.4039 0 ;
0.4363 0.7624 0 0 0 0.7165 0.5486 0 ;
0 0 0.7724 0 0.8531 0 0 0.9564;
0 0 0 0.6086 0 0 0.5527 0.9357]
Could you please help me on this.
You're probably on a version earlier than 2017b. Please fill the release field on the top right of the page.
On old versions, you'll have to use sort as shown by Geoff.
edit: Actually looking at your desired output, it's slightly more complicated:
[~, roworder] = sort(A, 1, 'descend');
A(sub2ind(size(A), roworder(4:end, :), repmat(1:size(A, 2), size(A, 1)-3, 1))) = 0

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Answer by Geoff Hayes
on 2 Jun 2019

jaah - try using sort to sort the columns of your matrix in descending order
B = sort(A, 'descend');
To set all but the first three columns to zero, then do
B(4:end,:) = 0;

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