Find first k largest elements?

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.

Answer 1

[Matt J]

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

[Rubel Ahmed]

@Matt J thanks but I have figured out this is also useful

[~, idx] = sort(A);

ans = A(sort(idx(end-2:end)));

[Matt J]

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.