How to find the multiple max values

say like I have this 2D matrix

11  2  3  6  
 5  6  9  8  
 9 55 11 12
80 14 15 16 
17 97 35 20 
21 22 23 27

and I want to find the 4 largest values in column 3. How do I do that? *I did read some of the other posts but I can't seem to find anything conclusive.

Answer 1

[Walter Roberson]

dvals = sort(YourMatrix(:,3), 'descend');
largest4 = dvals(1:4);

[Anonymous Matrix]

great! thanks! but just one more question if you don't mind. How do I get the indices? (i'm sorry if the answer is insanely obvious but i'm kinda sick so my brain isn't functioning really well right now)

[Walter Roberson]

 [dvals, dindex] = sort(YourMatrix(:,3), 'descend');
 largest4 = dvals(1:4);
 index_of_largest4 = dindex(1:4);

[jaah navi]

With respect to the matrix

[11  2  3  6;  
 5  6  9  8;  
 9 55 11 12;
80 14 15 16; 
17 97 35 20; 
21 22 23 27]

how to frame the matrix such that it should display with two maximum values of each column and the other values to be zero.

lets say the output should be in the following manner

[0 0 0 0;
 0 0 0 0;
 0 55 0 0;
 80 0 0 0;
 0 97 35 0;
 21 0 23 27]

Could you please help me on this.

[Walter Roberson]

What should be done if there are duplicate matches? Three all the same, or one max and two copies of second best?

[jaah navi]

with respect to the matrix

11  2  3  6  
 5  6  9  8  
 9 55 11 12
80 14 15 16 
17 97 35 20 
21 22 23 27

how to find the largest four values in all columns.

[Guillaume]

Since this old answer has been revived, note that since R2017b you can use maxk which may or may not be faster than sorting the whole array/column. See also topkrows (R2016b or later) which may have been the ultimate goal here.

[largest4, indexoflargest4] = maxk(Yourmatrix(:, 3), 4);
%or
[largest4rows, indices] = topkrows(Yourmatrix, 4, 3);

@Jaah navi, as usual, when wanting to operate on the whole matrix reshape it into a single column with (:).

[Walter Roberson]

What should be done if there are duplicate matches? Five all the same, or one max and four copies of second best, or one max and one second best and three copies of the third best, and so on? Your question contains no information about how you want to handle ties.

[Guillaume]

I found out later that the question was also asked here in more details. Asking the same questions in several places just duplicate efforts and waste people's time. Please don't do that.