How to find the number of occurrences of each pair in a matrix?

Suppose my

A = [1 2 3; 
     2 3 1; 
     2 1 3] 

 % where any digit won't repeat in the same row.
 % I need to find out the number of occurrences of each pair.

Expected output:

Pair(1,2) = 1 occurence; 
Pair(2,1) = 1;
Pair(2,3) = 2;
Pair(3,2) = 0;
Pair(3,1) = 1; 
Pair(1,3) = 1;

I was trying this code

    for n = 2:3
    [j,i]=ind2sub(fliplr(size(A)),  strfind(reshape(A.',1,[]),[1 n]).');
    C = [i,j];
    d = numel(C(j));
    T9 = table(1, n, d)
    end

error occurs when the second row ends with 1 and the third row begins with 2.

Answer 1

[Bruno Luong]

A = [1 2 3; 
     2 3 1; 
     2 1 3];

u = unique(A);
P = nchoosek(u,2);
P = [P;fliplr(P)];
[~,J] = ismember([A(:,1:2); A(:,2:3)],P,'rows');
n = accumarray(J(:),1,[size(P,1) 1]);
% 
for k=1:size(P,1)
    fprintf('Pair %s, %d time\n',mat2str(P(k,:)),n(k));
end

Output

Pair [1 2], 1 time
Pair [1 3], 1 time
Pair [2 3], 2 time
Pair [2 1], 1 time
Pair [3 1], 1 time
Pair [3 2], 0 time

Answer 2

[David Goodmanson]

Hi MSK,

nrow = size(A,1);
B = A(:);
s1 = full(sparse(B(1:end-nrow),B(nrow+1:end),1))

puts instances if i,j into entry i,j. This should work with any number n of columns, assuming numbers 1 through n are used in each row.