Add a useful package (from Source forge) for octave

[CreaPhase.git] / octave_packages / statistics-1.1.3 / nanmedian.m

diff --git a/octave_packages/statistics-1.1.3/nanmedian.m b/octave_packages/statistics-1.1.3/nanmedian.m
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+## Copyright (C) 2001 Paul Kienzle <pkienzle@users.sf.net>
+##
+## This program 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.
+##
+## This program 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
+## this program; if not, see <http://www.gnu.org/licenses/>.
+
+## -*- texinfo -*-
+## @deftypefn {Function File} @var{v} = nanmedian (@var{x})
+## @deftypefnx{Function File} @var{v} = nanmedian (@var{x}, @var{dim})
+## Compute the median of data while ignoring NaN values.
+##
+## This function is identical to the @code{median} function except that NaN values
+## are ignored.  If all values are NaN, the median is returned as NaN. 
+##
+## @seealso{median, nanmin, nanmax, nansum, nanmean}
+## @end deftypefn
+
+function v = nanmedian (X, varargin)
+  if nargin < 1 || nargin > 2
+    print_usage;
+  endif
+  if nargin < 2
+    dim = min(find(size(X)>1));
+    if isempty(dim), dim=1; endif;
+  else
+    dim = varargin{:};
+  endif
+
+  sz = size (X);
+  if (prod (sz) > 1)
+      ## Find lengths of datasets after excluding NaNs; valid datasets
+      ## are those that are not empty after you remove all the NaNs
+      n = sz(dim) - sum (isnan(X),varargin{:});
+
+      ## When n is equal to zero, force it to one, so that median
+      ## picks up a NaN value below
+      n (n==0) = 1;
+
+      ## Sort the datasets, with the NaN going to the end of the data
+      X = sort (X, varargin{:});
+
+      ## Determine the offset for each column in single index mode
+      colidx = reshape((0:(prod(sz) / sz(dim) - 1)), size(n)); 
+      colidx = floor(colidx / prod(sz(1:dim-1))) * prod(sz(1:dim)) + ...
+          mod(colidx,prod(sz(1:dim-1)));
+      stride = prod(sz(1:dim-1));
+
+      ## Average the two central values of the sorted list to compute
+      ## the median, but only do so for valid rows.  If the dataset
+      ## is odd length, the single central value will be used twice.
+      ## E.g., 
+      ##   for n==5, ceil(2.5+0.5) is 3 and floor(2.5+0.5) is also 3
+      ##   for n==6, ceil(3.0+0.5) is 4 and floor(3.0+0.5) is 3
+      ## correction made for stride of data "stride*ceil(2.5-0.5)+1"
+      v = (X(colidx + stride*ceil(n./2-0.5) + 1)  + ...
+           X(colidx + stride*floor(n./2-0.5) + 1)) ./ 2;
+  else
+    error ("nanmedian: invalid matrix argument");
+  endif
+endfunction