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## Copyright (C) 2000-2013 Paul Kienzle
## Copyright (C) 2008-2009 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} {} intersect (@var{a}, @var{b})
## @deftypefnx {Function File} {[@var{c}, @var{ia}, @var{ib}] =} intersect (@var{a}, @var{b})
##
## Return the elements in both @var{a} and @var{b}, sorted in ascending
## order. If @var{a} and @var{b} are both column vectors return a column
## vector, otherwise return a row vector.
## @var{a}, @var{b} may be cell arrays of string(s).
##
## Return index vectors @var{ia} and @var{ib} such that @code{a(ia)==c} and
## @code{b(ib)==c}.
##
## @end deftypefn
## @seealso{unique, union, setxor, setdiff, ismember}
function [c, ia, ib] = intersect (a, b, varargin)
if (nargin < 2 || nargin > 3)
print_usage ();
endif
[a, b] = validargs ("intersect", a, b, varargin{:});
if (isempty (a) || isempty (b))
c = ia = ib = [];
else
## form a and b into sets
if (nargout > 1)
[a, ja] = unique (a, varargin{:});
[b, jb] = unique (b, varargin{:});
else
a = unique (a, varargin{:});
b = unique (b, varargin{:});
endif
if (nargin > 2)
c = [a; b];
[c, ic] = sortrows (c);
ii = find (all (c(1:end-1,:) == c(2:end,:), 2));
c = c(ii,:);
len_a = rows (a);
else
c = [a(:); b(:)];
[c, ic] = sort (c); # [a(:);b(:)](ic) == c
if (iscellstr (c))
ii = find (strcmp (c(1:end-1), c(2:end)));
else
ii = find (c(1:end-1) == c(2:end));
endif
c = c(ii);
len_a = length (a);
endif
if (nargout > 1)
ia = ja(ic(ii)); # a(ia) == c
ib = jb(ic(ii+1) - len_a); # b(ib) == c
endif
if (nargin == 2 && (rows (b) == 1 || rows (a) == 1))
c = c.';
endif
endif
endfunction
%!# Test the routine for index vectors ia and ib
%!test
%! a = [3 2 4 5 7 6 5 1 0 13 13];
%! b = [3 5 12 1 1 7];
%! [c,ia,ib] = intersect (a, b);
%! assert (c, [1 3 5 7]);
%! assert (ia, [8 1 7 5]);
%! assert (ib, [5 1 2 6]);
%! assert (a(ia), c);
%! assert (b(ib), c);
%!test
%! a = [1,1,2;1,4,5;2,1,7];
%! b = [1,4,5;2,3,4;1,1,2;9,8,7];
%! [c,ia,ib] = intersect (a, b, "rows");
%! assert (c, [1,1,2;1,4,5]);
%! assert (ia, [1;2]);
%! assert (ib, [3;1]);
%! assert (a(ia,:), c);
%! assert (b(ib,:), c);
%!test
%! a = [1 1 1 2 2 2];
%! b = [1 2 3 4 5 6];
%! c = intersect (a, b);
%! assert(c, [1,2]);
%!test
%! a = [1 2 3 4; 5 6 7 8; 9 10 11 12];
%! [b, ia, ib] = intersect (a, a, "rows");
%! assert (b, a);
%! assert (ia, [1:3]');
%! assert (ib, [1:3]');
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