Source code in the octave programming language

function m = mode2(v)
  sv = sort(v);
  % build two vectors, vals and c, so that
  % c(i) holds how many times vals(i) appears
  i = 1; c = []; vals = [];
  while (i <= numel(v) )
    tc = sum(sv==sv(i)); % it would be faster to count
                         % them "by hand", since sv is sorted...
    c = [c, tc];
    vals = [vals, sv(i)];
    i += tc;
  endwhile
  % stack vals and c building a 2-rows matrix x
  x = cat(1,vals,c);
  % sort the second row (frequencies) into t (most frequent
  % first) and take the "original indices" i ... 
  [t, i] = sort(x(2,:), "descend");
  % ... so that we can use them to sort columns according
  % to frequencies
  nv = x(1,i);
  % at last, collect into m (the result) all the values
  % having the same bigger frequency
  r = t(1); i = 1;
  m = [];
  while ( t(i) == r )
    m = [m, nv(i)];
    i++;
  endwhile
endfunction


a = [1, 3, 6, 6, 6, 6, 7, 7, 12, 12, 17];
mode2(a)
mode(a)

a = [1, 1, 2, 4, 4];
mode2(a)    % returns 1 and 4
mode(a)     % returns 1 only