Find unique pairs in a matrix

Question

Let's assume I have the following matrix:

A = [1 1 2 1;1 2 2 1;2 1 3 0;2 2 2 0;3 1 2 1]

Where the first column is an index and the next two an interaction and the last one a logic saying yes or no. So know I would like to generate the following heat map based on the interactions. "X" axis represents interactions and "Y" axis represents index.

   1-2  1-3  2-2
1   1   NaN   1
2  NaN   0    0
3   1   NaN  NaN

My current approach:

B = sortrows(A,[2,3]);

Afterwards I apply find for each row and column individually.

Is there a function similar to unique which can check for two columns at the same time?

Answer 1

Here's a way, using unique(...,'rows'):

A = [1 1 2 1; 1 2 2 1; 2 1 3 0; 2 2 2 0; 3 1 2 1]; % data
[~, ~, jj] = unique(A(:,[2 3]),'rows'); % get interaction identifiers
B = accumarray([A(:,1) jj], A(:,4), [], @sum, NaN); % build result, with NaN as fill value

This gives

B =
     1   NaN     1
   NaN     0     0
     1   NaN   NaN