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New nthargout function * nthargout.m: New function. * func.txi (Multiple Return Values): document nthargout. * module.mk (general_FCN_FILES): Add nthargout.m * help.cc (varargin, varargout): Cross-reference other arg functions. * ov-user-fucn.cc (nargin, nargout, isargout): Ditto. * NEWS (3.6): Mention this new file.
author Jordi Gutiérrez Hermoso <jordigh@octave.org>
date Tue, 25 Oct 2011 09:46:38 -0700
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children 9cae456085c2
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1 ## Copyright (C) 2011 Jordi Gutiérrez Hermoso
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2 ##
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3 ## This file is part of Octave.
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4 ##
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5 ## Octave is free software; you can redistribute it and/or modify it
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6 ## under the terms of the GNU General Public License as published by
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7 ## the Free Software Foundation; either version 3 of the License, or (at
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8 ## your option) any later version.
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9 ##
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10 ## Octave is distributed in the hope that it will be useful, but
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11 ## WITHOUT ANY WARRANTY; without even the implied warranty of
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12 ## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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13 ## General Public License for more details.
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14 ##
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15 ## You should have received a copy of the GNU General Public License
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16 ## along with Octave; see the file COPYING. If not, see
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17 ## <http://www.gnu.org/licenses/>.
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18
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19 ## -*- texinfo -*-
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20 ## @deftypefn {Function File} {} nthargout (@var{n}, @var{func}, @dots{})
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21 ## @deftypefnx {Function File} {} nthargout (@var{n}, @var{ntot}, @var{func}, @dots{})
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22 ## Return the @var{n}th output argument of function given by the
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23 ## function handle or string @var{func}. Any arguments after @var{func}
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24 ## are passed to @var{func}. The total number of arguments to call
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25 ## @var{func} with can be passed in @var{ntot}; by default @var{ntot}
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26 ## is @var{n}. The input @var{n} can also be a vector of indices of the
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27 ## output, in which case the output will be a cell array of the
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28 ## requested output arguments.
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29 ##
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30 ## The intended use @code{nthargout} is to avoid intermediate variables.
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31 ## For example, when finding the indices of the maximum entry of a
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32 ## matrix, the following two compositions of nthargout
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33 ##
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34 ## @example
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35 ## @group
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36 ## @var{m} = magic (5);
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37 ## cell2mat (nthargout ([1, 2], @@ind2sub, size(@var{m}),
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38 ## nthargout (2, @@max, @var{m}(:))))
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39 ## @result{} 5 3
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40 ## @end group
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41 ## @end example
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42 ##
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43 ## @noindent
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44 ## are completely equivalent to the following lines:
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45 ##
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46 ## @example
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47 ## @group
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48 ## @var{m} = magic(5);
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49 ## [~, idx] = max (@var{M}(:));
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50 ## [i, j] = ind2sub (size (@var{m}), idx);
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51 ## [i, j]
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52 ## @result{} 5 3
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53 ## @end group
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54 ## @end example
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55 ##
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56 ## It can also be helpful to have all output arguments in a single cell
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57 ## in the following manner:
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58 ##
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59 ## @example
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60 ## @var{USV} = nthargout ([1:3], @@svd, hilb (5));
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61 ## @end example
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62 ##
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63 ## @seealso{nargin, nargout, varargin, varargout, isargout}
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64 ## @end deftypefn
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65
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66 ## Author: Jordi Gutiérrez Hermoso
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67
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68 function out = nthargout (n, varargin)
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69 if (nargin < 2)
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70 print_usage ();
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71 endif
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72
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73 if (isa (varargin{1}, "function_handle") || ischar (varargin{1}))
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74 ntot = max (n(:));
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75 func = varargin{1};
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76 args = varargin(2:end);
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77 elseif (isnumeric (varargin{1})
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78 && (isa (varargin{2}, "function_handle") || ischar (varargin{2})))
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79 ntot = varargin{1};
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80 func = varargin{2};
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81 args = varargin(3:end);
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82 else
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83 print_usage ();
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84 endif
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85
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86 if (any (n != fix (n)) || ntot != fix (ntot) || any (n <= 0) || ntot <= 0)
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87 error ("nthargout: N and NTOT must consist of positive integers")
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88 endif
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89
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90 outargs = cell (1, ntot);
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91
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92 try
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93 [outargs{:}] = feval (func, args{:});
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94 if (numel (n) > 1)
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95 out = outargs(n);
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96 else
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97 out = outargs{n};
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98 endif
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99 catch
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100 err = lasterr ();
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101 if (strfind ("some elements undefined in return list", err))
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102 error ("nthargout: Too many output arguments: %d", ntot);
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103 else
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104 error (err);
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105 endif
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106 end_try_catch
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107
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108 endfunction
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109
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110 %!shared m
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111 %! m = magic (5);
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112 %!assert (nthargout ([1, 2], @ind2sub, size(m), nthargout (2, @max, m(:))), {5,3})
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113 %!assert (nthargout (3, @find, m(m>20)), [23, 24, 25, 21, 22]')