## Copyright (C) 2000, 2005, 2007, 2008 Daniel Calvelo
## Copyright (C) 2009 Jaroslav Hajek
##
## 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
## <http://www.gnu.org/licenses/>.

## -*- texinfo -*-
## @deftypefn {Function File} {} sortrows (@var{a}, @var{c})
## Sort the rows of the matrix @var{a} according to the order of the
## columns specified in @var{c}.  If @var{c} is omitted, a
## lexicographical sort is used. By default ascending order is used 
## however if elements of @var{c} are negative then the corresponding  
## column is sorted in descending order.
## @end deftypefn

## Author: Daniel Calvelo, Paul Kienzle
## Adapted-by: jwe

function [s, i] = sortrows (m, c)

  default_mode = "ascend";
  other_mode = "descend";

  if (issparse (m))
    error ("sortrows: sparse matrices not yet supported");
  endif

  ## If the sort is homogeneous, we use the built-in faster algorithm.
  if (nargin == 1)
    i = __sort_rows_idx__ (m, default_mode);
  elseif (all (c > 0))
    i = __sort_rows_idx__ (m(:,c), default_mode);
  elseif (all (c < 0))
    i = __sort_rows_idx__ (m(:,-c), other_mode);
  else
    ## Otherwise, fall back to the old algorithm
    for ii = 1:length (c);
      if (c(ii) < 0)
        mode{ii} = other_mode;
      else
        mode{ii} = default_mode;
      endif
    endfor
    indices = abs(c(:));

    ## Since sort is 'stable' the order of identical elements will be
    ## preserved, so by traversing the sort indices in reverse order we
    ## will make sure that identical elements in index i are subsorted by
    ## index j.
    indices = flipud (indices);
    mode = flipud (mode');
    i = [1:size(m,1)]';
    for ii = 1:length (indices);
      [trash, idx] = sort (m(i, indices(ii)), mode{ii});
      i = i(idx);
    endfor
  endif

  s = m(i,:);

endfunction

%!shared x, idx
%! [x, idx] = sortrows ([1, 1; 1, 2; 3, 6; 2, 7], [1, -2]);
%!assert (x, [1, 2; 1, 1; 2, 7; 3, 6]);
%!assert (idx, [2; 1; 4; 3]);