findout the second largest element in each row and its location in a matrix

I have a (3*5) matrix i.e A=[1 2 3 4 5, 6 7 9 8 10, 11 12 14 13 15], i would like to find out the second largest element in each row and its location in the matrix. i expect 2 outputs 1)second_maxvalue_A=[4,9,14] 2)location_of_second_maxval=[4,3,3]

Answer 1

[Guillaume]

One possible way is to find the largest values, replace them with a very small value (-Inf) and search for the new largest values:

A=[1 2 3 4 5; 6 7 9 8 10; 11 12 14 13 15] %your example A was a single row
m = max(A, [], 2); %find the max in each row
A(bsxfun(@eq, A, m)) = -Inf; %replace the max(s) by -Inf
m = max(A, [], 2)  %find the new max which is the second largest.

[navan]

 Thanks Guillaume,

That works.thanks alot

[zahra najjar]

what about the place!

[Bruno Luong]

zahra najja: Please read the other ANSWERS bellow, or even better the DOC of MIN

Answer 2

[Steven Lord]

If you're using release R2017b or later, use maxk.

Answer 3

[Thomas Koelen]

Edit: seems like I misread second largest...

, should be ;.

A=[1 2 3 4 5; 6 7 9 8 10; 11 12 14 13 15];
[m,i] = max(A,[],2)

gives you:

m =

     5
    10
    15

i =

     5
     5
     5

example:

A=rand(3,5);
[m,i] = max(A,[],2)

gives:

    0.8147    0.9134    0.2785    0.9649    0.9572
    0.9058    0.6324    0.5469    0.1576    0.4854
    0.1270    0.0975    0.9575    0.9706    0.8003

m =

    0.9649
    0.9058
    0.9706

i =

     4
     1
     4

[Thomas Koelen]

Finding second or third biggest can be done this way:

m=3;n=4;ggg = rand(m,n);
[svals,idx] = sort(ggg(:),'descend'); % sort to vector
svals(2) % second largest value
[II,JJ] = ind2sub([m,n],idx(2)) % position in the matrix

[Guillaume]

Doesn't this find the second largest element in the matrix, rather than each row?

Secondly, if there are more than one element equal to the max, it still returns the max.

[Guillaume]

A generic way of finding the nth largest value of each row, if it exists:

function nl = nthlargestrow(m, n)
   %m:  a 2d matrix to search
   %n:  an integer
   %nl: cell array containing the nth largest value of each row. If a row does not have n different values, the cell is empty
   nl = cell(size(m, 1), 1);
   u = cellfun(@unique, num2cell(m, 2), 'UniformOutput', false);
   hasnelements = cellfun(@numel, u) >= n;
   nl(hasnelements) = cellfun(@(row) row(end-n+1), u(hasnelements), 'UniformOutput', false)
end

Answer 4

[Thorsten]

A=[1 2 3 4 5; 6 7 9 8 10; 11 12 14 13 15];
% remove highest value in each row
sz = size(A);
[~, ind] = max(A, [], 2);
ind = ind + [0; cumsum(repmat(sz(2), [sz(1)-1 1]))];
A = A';
A(ind) = [];
A = reshape(A, [sz(2)-1 sz(1)])';
% find highest value in each row (i.e., second largest of original matrix)
[max2, ind2] = max(A, [], 2);