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## -*- texinfo -*-
## @deftypefn  {} {@var{m} =} mode (@var{x})
## @deftypefnx {} {@var{m} =} mode (@var{x}, @var{dim})
## @deftypefnx {} {[@var{m}, @var{f}, @var{c}] =} mode (@dots{})
## Compute the most frequently occurring value in a dataset (mode).
##
## @code{mode} determines the frequency of values along the first non-singleton
## dimension and returns the value with the highest frequency.  If two, or
## more, values have the same frequency @code{mode} returns the smallest.
##
## If the optional argument @var{dim} is given, operate along this dimension.
##
## The return variable @var{f} is the number of occurrences of the mode in
## the dataset.
##
## The cell array @var{c} contains all of the elements with the maximum
## frequency.
## @seealso{mean, median}
## @end deftypefn

function [m, f, c] = mode (x, dim)

  if (nargin < 1)
    print_usage ();
  endif

  if (! (isnumeric (x) || islogical (x)))
    error ("mode: X must be a numeric vector or matrix");
  endif

  nd = ndims (x);
  sz = size (x);
  if (nargin < 2)
    ## Find the first non-singleton dimension.
    (dim = find (sz != 1, 1)) || (dim = 1);
  else
    if (! (isscalar (dim) && dim > 0 && rem (dim, 1) == 0))
      error ("mode: DIM must be an integer and a valid dimension");
    endif
  endif

  if (isempty (x))
    ## Empty x produces NaN for m, 0 for f, , but m, f and c
    ## shape depends on size of x.
    if ((nargin == 1) && (nd == 2) && (sz == [0 0]))
      f = 0; # f always a double even if x is single.
      if (isa (x, "single"))
        m = NaN ("single");
        c = {(NaN (0, 1, "single"))};
      else
        m = NaN;
        c = {(NaN (0, 1))};
      endif
    else
      sz(dim) = 1;
      f = zeros (sz); # f always a double even if x is single.
      c = cell (sz);
      if (isa (x, "single"))
        m = (NaN (sz, "single"));
        c(:) = NaN (1, 0, "single");
      else
        m = NaN (sz);
        c(:) = NaN (1, 0);
      endif
    endif
    return;
  endif

  if (dim > nd || sz(dim) == 1)
    ## Special case of mode over singleton dimension.
    m = x;
    f = ones (size (x));
    c = num2cell (x);
    return;
  endif

  sz2 = sz;
  sz2(dim) = 1;
  sz3 = ones (1, nd);
  sz3(dim) = sz(dim);

  if (issparse (x))
    t2 = sparse (sz(1), sz(2));
  else
    t2 = zeros (sz);
  endif

  if (dim != 1)
    perm = [dim, 1:dim-1, dim+1:nd];
    t2 = permute (t2, perm);
  endif

  xs = sort (x, dim);
  t = cat (dim, true (sz2), diff (xs, 1, dim) != 0);

  if (dim != 1)
    t2(permute (t != 0, perm)) = diff ([find(permute (t, perm))(:); prod(sz)+1]);
    f = max (ipermute (t2, perm), [], dim);
    xs = permute (xs, perm);
  else
    t2(t) = diff ([find(t)(:); prod(sz)+1]);
    f = max (t2, [], dim);
  endif

  c = cell (sz2);
  if (issparse (x))
    m = sparse (sz2(1), sz2(2));
  else
    m = zeros (sz2, class (x));
  endif
  for i = 1 : prod (sz2)
    c{i} = xs(t2(:, i) == f(i), i);
    m(i) = c{i}(1);
  endfor

endfunction


%!test
%! [m, f, c] = mode (toeplitz (1:5));
%! assert (m, [1,2,2,2,1]);
%! assert (f, [1,2,2,2,1]);
%! assert (c, {[1;2;3;4;5],[2],[2;3],[2],[1;2;3;4;5]});
%!test
%! [m, f, c] = mode (toeplitz (1:5), 2);
%! assert (m, [1;2;2;2;1]);
%! assert (f, [1;2;2;2;1]);
%! assert (c, {[1;2;3;4;5];[2];[2;3];[2];[1;2;3;4;5]});
%!test
%! a = sprandn (32, 32, 0.05);
%! sp0 = sparse (0);
%! [m, f, c] = mode (a);
%! [m2, f2, c2] = mode (full (a));
%! assert (m, sparse (m2));
%! assert (f, sparse (f2));
%! c_exp(1:length (a)) = { sp0 };
%! assert (c ,c_exp);
%! assert (c2,c_exp);

%!assert (mode ([2,3,1,2,3,4],1),[2,3,1,2,3,4])
%!assert (mode ([2,3,1,2,3,4],2),2)
%!assert (mode ([2,3,1,2,3,4]),2)
%!assert (mode (single ([2,3,1,2,3,4])), single (2))
%!assert (mode (int8 ([2,3,1,2,3,4])), int8 (2))

%!assert (mode ([2;3;1;2;3;4],1),2)
%!assert (mode ([2;3;1;2;3;4],2),[2;3;1;2;3;4])
%!assert (mode ([2;3;1;2;3;4]),2)

%!test
%! x = magic (3);
%! [m, f, c] = mode (x, 3);
%! assert (m, x);
%! assert (f, ones (3,3));
%! assert (c, num2cell (x));

%!test
%! x = single (magic (3));
%! [m, f, c] = mode (x, 3);
%! assert (class (m), "single");
%! assert (class (f), "double");
%! assert (class (c), "cell");
%! assert (class (c(1)), "cell");
%! assert (class (c{1}), "single");

%!shared x
%! x(:,:,1) = toeplitz (1:3);
%! x(:,:,2) = circshift (toeplitz (1:3), 1);
%! x(:,:,3) = circshift (toeplitz (1:3), 2);
%!test
%! [m, f, c] = mode (x, 1);
%! assert (reshape (m, [3, 3]), [1 1 1; 2 2 2; 1 1 1]);
%! assert (reshape (f, [3, 3]), [1 1 1; 2 2 2; 1 1 1]);
%! c = reshape (c, [3, 3]);
%! assert (c{1}, [1; 2; 3]);
%! assert (c{2}, 2);
%! assert (c{3}, [1; 2; 3]);
%!test
%! [m, f, c] = mode (x, 2);
%! assert (reshape (m, [3, 3]), [1 1 2; 2 1 1; 1 2 1]);
%! assert (reshape (f, [3, 3]), [1 1 2; 2 1 1; 1 2 1]);
%! c = reshape (c, [3, 3]);
%! assert (c{1}, [1; 2; 3]);
%! assert (c{2}, 2);
%! assert (c{3}, [1; 2; 3]);
%!test
%! [m, f, c] = mode (x, 3);
%! assert (reshape (m, [3, 3]), [1 2 1; 1 2 1; 1 2 1]);
%! assert (reshape (f, [3, 3]), [1 2 1; 1 2 1; 1 2 1]);
%! c = reshape (c, [3, 3]);
%! assert (c{1}, [1; 2; 3]);
%! assert (c{2}, [1; 2; 3]);
%! assert (c{3}, [1; 2; 3]);
%!shared   ## Clear shared to prevent variable echo for any later test failures

## Test empty inputs
%!test <*48690>
%! [m, f, c] = mode ([]);
%! assert (m, NaN);
%! assert (f, 0);
%! assert (c, {(NaN (0, 1))});
%!test <*48690>
%! [m, f, c] = mode (single ([]));
%! assert (class (m), "single");
%! assert (class (f), "double");
%! assert (c, {(single (NaN (0, 1)))});
%!test <*48690>
%! [m, f, c] = mode ([], 1);
%! assert (m, NaN (1, 0));
%! assert (f, zeros (1, 0));
%! assert (c, cell (1, 0));
%!test <*48690>
%! [m, f, c] = mode ([], 2);
%! assert (m, NaN (0, 1));
%! assert (f, zeros (0, 1));
%! assert (c, cell(0, 1));
%!test <*48690>
%! [m, f, c] = mode ([], 3);
%! assert (m, []);
%! assert (f, []);
%! assert (c, cell (0, 0));
%!test <*48690>
%! [m, f, c] = mode (ones (0, 1));
%! assert (m, NaN);
%! assert (f, 0);
%! assert (c, {(NaN (1, 0))});
%!test <*48690>
%! [m, f, c] = mode (ones (0, 1), 1);
%! assert (m, NaN);
%! assert (f, 0);
%! assert (c, {(NaN (1, 0))});
%!test <*48690>
%! [m, f, c] = mode (ones (0, 1), 2);
%! assert (m, NaN (0, 1));
%! assert (f, zeros (0, 1));
%! assert (c, cell (0, 1));
%!test <*48690>
%! [m, f, c] = mode (ones (0, 1), 3);
%! assert (m, NaN (0, 1));
%! assert (f, zeros (0, 1));
%! assert (c, cell (0, 1));
%!test <*48690>
%! [m, f, c] = mode (ones (1, 0));
%! assert (m, NaN);
%! assert (f, 0);
%! assert (c, {(NaN (1, 0))});
%!test <*48690>
%! [m, f, c] = mode (ones (1, 0), 1);
%! assert (m, NaN (1, 0));
%! assert (f, zeros (1, 0));
%! assert (c, cell (1, 0));
%!test <*48690>
%! [m, f, c] = mode (ones (1, 0), 2);
%! assert (m, NaN);
%! assert (f, 0);
%! assert (c, {(NaN (1, 0))});
%!test <*48690>
%! [m, f, c] = mode (ones (1, 0), 3);
%! assert (m, NaN (1, 0));
%! assert (f, zeros (1, 0));
%! assert (c, cell (1, 0));
%!test <*48690>
%! [m, f, c] = mode (ones (0, 0, 0));
%! assert (m, NaN (1, 0, 0));
%! assert (f, zeros (1, 0, 0));
%! assert (c, cell (1, 0, 0));
%!test <*48690>
%! [m, f, c] = mode (ones (0, 0, 0), 1);
%! assert (m, NaN (1, 0, 0));
%! assert (f, zeros (1, 0, 0));
%! assert (c, cell (1, 0, 0));
%!test <*48690>
%! [m, f, c] = mode (ones (0, 0, 0), 2);
%! assert (m, NaN (0, 1, 0));
%! assert (f, zeros (0, 1, 0));
%! assert (c, cell (0, 1, 0));
%!test <*48690>
%! [m, f, c] = mode (ones (0, 0, 0), 3);
%! assert (m, NaN (0, 0, 1));
%! assert (f, zeros (0, 0, 1));
%! assert (c, cell (0, 0, 1));
%!test <*48690>
%! [m, f, c] = mode (ones (1, 5, 0), 2);
%! assert (m, NaN (1, 1, 0));
%! assert (f, zeros (1, 1, 0));
%! assert (c, cell (1, 1, 0));
%!test <*48690>
%! [m, f, c] = mode (ones (5, 1, 0), 2);
%! assert (m, NaN (5, 1, 0));
%! assert (f, zeros (5, 1, 0));
%! assert (c, cell (5, 1, 0));
%!test <*48690>
%! [m, f, c] = mode (ones (2, 0));
%! assert (m, NaN (1, 0));
%! assert (f, zeros (1, 0));
%! assert (c, cell (1, 0));
%!test <*48690>
%! [m, f, c] = mode (ones (0, 2));
%! assert (m, NaN (1, 2));
%! assert (f, zeros (1, 2));
%! assert (c, {(NaN (1, 0)),(NaN (1, 0))});
%!test <*48690>
%! [m, f, c] = mode (ones (1, 1, 1, 0));
%! assert (m, NaN (1, 1));
%! assert (f, zeros (1, 1));
%! assert (c, {(NaN (1, 0))});
%!test <*48690>
%! [m, f, c] = mode (ones (1, 1, 1, 0), 1);
%! assert (m, NaN (1, 1, 1, 0));
%! assert (f, zeros (1, 1, 1, 0));
%! assert (c, cell (1,1,1,0));

## Test input validation
%!error <Invalid call> mode ()
%!error <X must be a numeric> mode ({1 2 3})
%!error <DIM must be an integer> mode (1, ones (2,2))
%!error <DIM must be an integer> mode (1, 1.5)
%!error <DIM must be .* a valid dimension> mode (1, 0)
%!error <DIM must be .* a valid dimension> mode (1, -1)
%!error <DIM must be .* a valid dimension> mode (1, -1.5)
%!error <DIM must be .* a valid dimension> mode (1, Inf)
%!error <DIM must be .* a valid dimension> mode (1, NaN)