[Octave-cvsupdate] SF.net SVN: octave:[7956] trunk/octave-forge/main/statistics

[<ha...@us...>]

Revision: 7956
          http://octave.svn.sourceforge.net/octave/?rev=7956&view=rev
Author:   hauberg
Date:     2010-11-26 22:07:52 +0000 (Fri, 26 Nov 2010)

Log Message:
-----------
New function: combnk

Modified Paths:
--------------
    trunk/octave-forge/main/statistics/INDEX

Added Paths:
-----------
    trunk/octave-forge/main/statistics/inst/combnk.m

Modified: trunk/octave-forge/main/statistics/INDEX
===================================================================
--- trunk/octave-forge/main/statistics/INDEX	2010-11-26 16:56:40 UTC (rev 7955)
+++ trunk/octave-forge/main/statistics/INDEX	2010-11-26 22:07:52 UTC (rev 7956)
@@ -42,6 +42,7 @@
  trimmean	
  zscore	
  tabulate
+ combnk
 Experimental design
  fullfact ff2n
 Linear regression

Added: trunk/octave-forge/main/statistics/inst/combnk.m
===================================================================
--- trunk/octave-forge/main/statistics/inst/combnk.m	                        (rev 0)
+++ trunk/octave-forge/main/statistics/inst/combnk.m	2010-11-26 22:07:52 UTC (rev 7956)
@@ -0,0 +1,82 @@
+## Copyright (C) 2010  Soren Hauberg
+##
+## 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{c} =} combnk (@var{data}, @var{k})
+## Return all combinations of @var{k} elements in @var{data}.
+## @end deftypefn
+
+function retval = combnk (data, k)
+  ## Check input
+  if (! isvector (data))
+    error ("combnk: first input argument must be a vector");
+  endif 
+
+  if (!isreal (k) || k != round (k) || k < 0)
+    error ("combnk: second input argument must be a non-negative integer");
+  endif
+
+  ## Simple checks
+  n = numel (data);
+  if (k == 0 || k > n)
+    retval = resize (data, 0, k);
+  elseif (k == n)
+    retval = data (:).';
+  else
+    retval = __combnk__ (data, k);
+  endif
+
+  ## For some odd reason Matlab seems to treat strings differently compared to other data-types...
+  if (ischar (data))
+     retval = flipud (retval);
+  endif
+endfunction
+
+function retval = __combnk__ (data, k)
+  ## Recursion stopping criteria
+  if (k == 1)
+    retval = data (:);
+  else
+    ## Process data
+    n = numel (data);
+    retval = [];
+    for j = 1:n
+      C = __combnk__ (data ((j+1):end), k-1);
+      C = cat (2, repmat (data (j), rows (C), 1), C);
+      retval = [retval; C];
+    endfor
+  endif
+endfunction
+
+%!demo
+%! c = combnk (1:5, 2);
+%! disp ("All pairs of integers between 1 and 5:");
+%! disp (c);
+
+%!test
+%! c = combnk (1:3, 2);
+%! assert (c, [1, 2; 1, 3; 2, 3]);
+
+%!test
+%! c = combnk (1:3, 6);
+%! assert (isempty (c));
+
+%!test
+%! c = combnk ({1, 2, 3}, 2);
+%! assert (c, {1, 2; 1, 3; 2, 3});
+
+%!test
+%! c = combnk ("hello", 2);
+%! assert (c, ["lo"; "lo"; "ll"; "eo"; "el"; "el"; "ho"; "hl"; "hl"; "he"]);


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