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########################################################################
##
## Copyright (C) 2004-2024 The Octave Project Developers
##
## See the file COPYRIGHT.md in the top-level directory of this
## distribution or <https://octave.org/copyright/>.
##
## This file is part of Octave.
##
## Octave is free software: you can redistribute it and/or modify it
## under the terms of the GNU General Public License as published by
## the Free Software Foundation, either version 3 of the License, or
## (at your option) any later version.
##
## Octave is distributed in the hope that it will be useful, but
## WITHOUT ANY WARRANTY; without even the implied warranty of
## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
## GNU General Public License for more details.
##
## You should have received a copy of the GNU General Public License
## along with Octave; see the file COPYING. If not, see
## <https://www.gnu.org/licenses/>.
##
########################################################################
## -*- texinfo -*-
## @deftypefn {} {@var{B} =} flip (@var{A})
## @deftypefnx {} {@var{B} =} flip (@var{A}, @var{dim})
## Return a copy of array @var{A} flipped across dimension @var{dim}.
##
## If @var{dim} is unspecified it defaults to the first non-singleton
## dimension.
##
## Examples:
##
## @example
## ## row vector
## flip ([1 2 3 4])
## @result{} 4 3 2 1
##
## ## column vector
## flip ([1; 2; 3; 4])
## @result{} 4
## 3
## 2
## 1
##
## ## 2-D matrix along dimension 1
## flip ([1 2; 3 4])
## @result{} 3 4
## 1 2
##
## ## 2-D matrix along dimension 2
## flip ([1 2; 3 4], 2)
## @result{} 2 1
## 4 3
## @end example
##
## @seealso{fliplr, flipud, rot90, rotdim, permute, transpose}
## @end deftypefn
function B = flip (A, dim)
if (nargin < 1)
print_usage ();
endif
nd = ndims (A);
sz = size (A);
if (nargin == 1)
## Find the first non-singleton dimension.
(dim = find (sz > 1, 1)) || (dim = 1);
elseif (! (isscalar (dim) && isindex (dim)))
error ("flip: DIM must be a positive integer");
endif
idx(1:max(nd, dim)) = {':'};
idx{dim} = size (A, dim):-1:1;
B = A(idx{:});
endfunction
%!assert (flip ([1 2; 3 4], 2), [2 1; 4 3])
%!assert (flip ([1 2; 3 4], 3), [1 2; 3 4])
## Test defaults
%!assert (flip ([1 2 3 4]), [4 3 2 1])
%!assert (flip ([1 2 3 4].'), [4 3 2 1].')
%!assert (flip ([1 2; 3 4]), flip ([1 2 ; 3 4], 1))
## Test NDArrays
%!test
%! a(1:2,1:2,1) = [1 2; 3 4];
%! a(1:2,1:2,2) = [5 6; 7 8];
%! b(1:2,1:2,1) = [5 6; 7 8];
%! b(1:2,1:2,2) = [1 2; 3 4];
%! assert (flip (a, 3), b);
%!test
%! a = b = zeros (2, 2, 1, 2);
%! a(1:2,1:2,:,1) = [1 2; 3 4];
%! a(1:2,1:2,:,2) = [5 6; 7 8];
%! b(1:2,1:2,:,1) = [5 6; 7 8];
%! b(1:2,1:2,:,2) = [1 2; 3 4];
%! assert (flip (a, 3), a);
%! assert (flip (a, 4), b);
%! assert (flip (a, 5), a);
%!error <Invalid call> flip ()
%!error <DIM must be a positive integer> flip (magic (3), -1)
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