Mercurial > hg > octave-avbm
view scripts/statistics/base/median.m @ 7017:a1dbe9d80eee
[project @ 2007-10-12 21:27:11 by jwe]
author | jwe |
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date | Fri, 12 Oct 2007 21:27:37 +0000 |
parents | 93c65f2a5668 |
children | 83a8781b529d |
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## Copyright (C) 1996, 1997, 1998, 1999, 2000, 2004, 2005, 2006, 2007 ## John W. Eaton ## ## 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}, @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 ## @iftex ## @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 ## @end iftex ## @ifinfo ## ## @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 ifinfo ## 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{std, mean} ## @end deftypefn ## Author: jwe function retval = median (a, dim) if (nargin != 1 && nargin != 2) print_usage (); endif if (nargin < 2) dim = find (size (a) > 1, 1); if (isempty (dim)) dim = 1; endif endif sz = size (a); s = sort (a, dim); if (numel (a) > 0) if (numel (a) == sz(dim)) if (rem (sz(dim), 2) == 0) i = sz(dim) / 2; retval = (s(i) + s(i+1)) / 2; else i = ceil (sz(dim) /2); retval = s(i); endif else idx = cell (); nd = length (sz); for i = 1:nd idx{i} = 1:sz(i); endfor if (rem (sz(dim), 2) == 0) i = sz(dim) / 2; idx{dim} = i; retval = s(idx{:}); idx{dim} = i+1; retval = (retval + s(idx{:})) / 2; else idx{dim} = ceil (sz(dim) / 2); retval = s(idx{:}); endif endif else error ("median: invalid matrix argument"); endif endfunction