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author | Rik <octave@nomad.inbox5.com> |
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date | Mon, 26 Jul 2010 21:25:36 -0700 |
parents | a8ce6bdecce5 |
children | 2b03258c240b |
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## Copyright (C) 1996, 1997, 1998, 1999, 2000, 2004, 2005, 2006, 2007, ## 2008, 2009 John W. Eaton ## Copyright (C) 2009, 2010 VZLU Prague ## ## 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} {} median (@var{x}) ## @deftypefnx {Function File} {} median (@var{x}, @var{dim}) ## If @var{x} is a vector, compute the median value of the elements of ## @var{x}. If the elements of @var{x} are sorted, the median is defined ## as ## @tex ## $$ ## {\rm median} (x) = ## \cases{x(\lceil N/2\rceil), & $N$ odd;\cr ## (x(N/2)+x(N/2+1))/2, & $N$ even.} ## $$ ## @end tex ## @ifnottex ## ## @example ## @group ## x(ceil(N/2)), N odd ## median(x) = ## (x(N/2) + x((N/2)+1))/2, N even ## @end group ## @end example ## ## @end ifnottex ## If @var{x} is a matrix, compute the median value for each ## column and return them in a row vector. If the optional @var{dim} ## argument is given, operate along this dimension. ## @seealso{mean,mode} ## @end deftypefn ## Author: jwe function retval = median (a, dim) if (nargin != 1 && nargin != 2) print_usage (); endif if (nargin < 2) [~, dim] = max (size (a) != 1); # First non-singleton dim. endif if (numel (a) > 0) n = size (a, dim); k = floor ((n+1) / 2); if (mod (n, 2) == 1) retval = nth_element (a, k, dim); else retval = mean (nth_element (a, k:k+1, dim), dim); endif ## Inject NaNs where needed, to be consistent with Matlab. retval(any (isnan (a), dim)) = NaN; else error ("median: invalid matrix argument"); endif endfunction %!test %! x = [1, 2, 3, 4, 5, 6]; %! x2 = x'; %! y = [1, 2, 3, 4, 5, 6, 7]; %! y2 = y'; %! %! assert((median (x) == median (x2) && median (x) == 3.5 %! && median (y) == median (y2) && median (y) == 4 %! && median ([x2, 2*x2]) == [3.5, 7] %! && median ([y2, 3*y2]) == [4, 12])); %!error median (); %!error median (1, 2, 3);