Find first k largest elements?

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Rubel Ahmed
Rubel Ahmed 2021-8-13
评论： Matt J 2021-8-13
Hi all
I have an array say A = [1 5 7 4 8 10 14]. I want to find most largest, second most largest and 3rd most largest elements from A.
I have figured out that it can be done using maxk function which is abailable for update version of Matlab but I am using R2017a where maxk function is not availablle.
Anyway, I want to see the output like Ans = [14 10 8]. Please help.Thanks in advance.

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采纳的回答

Matt J
Matt J 2021-8-13
编辑：Matt J 2021-8-13
Ran in:
The efficient way would probably be to use a File Exchange MEX alternative to maxk() like this,
https://www.mathworks.com/matlabcentral/fileexchange/23576-min-max-selection?s_tid=srchtitle
but you could also do,
A = [1 5 7 4 8 10 14];
B=sort(A,'descend');
B=B(1:3)
B = 1×3
14 10 8
  2 个评论
Rubel Ahmed
Rubel Ahmed 2021-8-13
@Matt J thanks but I have figured out this is also useful
[~, idx] = sort(A);
ans = A(sort(idx(end-2:end)));
Matt J
Matt J 2021-8-13
Ran in:
I wouldn't recommend that.
A=rand(3e7,1);
tic;
B=maxk(A,3);
toc
Elapsed time is 0.039257 seconds.
tic;
B=sort(A,'descend');
B=B(1:3);
toc;
Elapsed time is 1.968519 seconds.
tic;
[~,idx]=sort(A);
B=A(idx(end:end-2));
toc
Elapsed time is 2.338227 seconds.

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