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## Copyright (C) 2012-2013 Jordi Gutiérrez Hermoso
##
## 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} {} nthargout (@var{n}, @var{func}, @dots{})
## @deftypefnx {Function File} {} nthargout (@var{n}, @var{ntot}, @var{func}, @dots{})
## Return the @var{n}th output argument of function given by the
## function handle or string @var{func}. Any arguments after @var{func}
## are passed to @var{func}. The total number of arguments to call
## @var{func} with can be passed in @var{ntot}; by default @var{ntot}
## is @var{n}. The input @var{n} can also be a vector of indices of the
## output, in which case the output will be a cell array of the
## requested output arguments.
##
## The intended use @code{nthargout} is to avoid intermediate variables.
## For example, when finding the indices of the maximum entry of a
## matrix, the following two compositions of nthargout
##
## @example
## @group
## @var{m} = magic (5);
## cell2mat (nthargout ([1, 2], @@ind2sub, size (@var{m}),
## nthargout (2, @@max, @var{m}(:))))
## @result{} 5 3
## @end group
## @end example
##
## @noindent
## are completely equivalent to the following lines:
##
## @example
## @group
## @var{m} = magic (5);
## [~, idx] = max (@var{M}(:));
## [i, j] = ind2sub (size (@var{m}), idx);
## [i, j]
## @result{} 5 3
## @end group
## @end example
##
## It can also be helpful to have all output arguments in a single cell
## in the following manner:
##
## @example
## @var{USV} = nthargout ([1:3], @@svd, hilb (5));
## @end example
##
## @seealso{nargin, nargout, varargin, varargout, isargout}
## @end deftypefn
## Author: Jordi Gutiérrez Hermoso
function out = nthargout (n, varargin)
if (nargin < 2)
print_usage ();
endif
if (isa (varargin{1}, "function_handle") || ischar (varargin{1}))
ntot = max (n(:));
func = varargin{1};
args = varargin(2:end);
elseif (isnumeric (varargin{1})
&& (isa (varargin{2}, "function_handle") || ischar (varargin{2})))
ntot = varargin{1};
func = varargin{2};
args = varargin(3:end);
else
print_usage ();
endif
if (any (n != fix (n)) || ntot != fix (ntot) || any (n <= 0) || ntot <= 0)
error ("nthargout: N and NTOT must consist of positive integers");
endif
outargs = cell (1, ntot);
try
[outargs{:}] = feval (func, args{:});
if (numel (n) > 1)
out = outargs(n);
else
out = outargs{n};
endif
catch
err = lasterr ();
if (strfind ("some elements undefined in return list", err))
error ("nthargout: Too many output arguments: %d", ntot);
else
error (err);
endif
end_try_catch
endfunction
%!shared m
%! m = magic (5);
%!assert (nthargout ([1,2], @ind2sub, size (m), nthargout (2, @max, m(:))), {5,3})
%!assert (nthargout (3, @find, m(m>20)), [23, 24, 25, 21, 22]')
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