Add a useful package (from Source forge) for octave

[CreaPhase.git] / octave_packages / strings-1.1.0 / editdistance.m

diff --git a/octave_packages/strings-1.1.0/editdistance.m b/octave_packages/strings-1.1.0/editdistance.m
new file mode 100644 (file)
index 0000000..45269d8
--- /dev/null
+++ b/octave_packages/strings-1.1.0/editdistance.m
@@ -0,0 +1,79 @@
+## Copyright (C) 2006 Muthiah Annamalai <muthiah.annamalai@uta.edu>
+##
+## 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{dist},@var{L}] =} editdistance (@var{string1}, @var{string2}, @var{weights})
+## Compute the Levenshtein edit distance between the strings @var{string1} and
+## @var{string2}. This operation is symmetrical.
+##
+## The optional argument @var{weights} specifies weights for the
+## deletion, matched, and insertion operations; by default it is set to
+## +1, 0, +1 respectively, so that a least editdistance means a 
+## closer match between the two strings. This function implements
+## the Levenshtein edit distance as presented in Wikipedia article,
+## accessed Nov 2006. Also the levenshtein edit distance of a string
+## with an empty string is defined to be its length.
+## 
+## The default return value is @var{dist} the edit distance, and
+## the other return value  @var{L} is the distance matrix.
+##
+## @example
+## @group
+##          editdistance('marry','marie') 
+##          ##returns value +2 for the distance.
+## @end group
+## @end example
+##
+## @end deftypefn
+
+function [dist, L] = editdistance (str1, str2, weights)
+  if(nargin < 2 || (nargin == 3 && length(weights)  < 3) )
+    print_usage();
+  end
+  
+  L1=length(str1)+1;
+  L2=length(str2)+1;
+  L=zeros(L1,L2);
+  
+  if(nargin < 3)
+    g=+1;%insertion
+    m=+0;%match
+    d=+1;%deletion
+  else
+    g=weights(1);
+    m=weights(2);
+    d=weights(3);
+  end
+
+  L(:,1)=[0:L1-1]'*g;
+  L(1,:)=[0:L2-1]*g;
+  
+  m4=0;
+  for idx=2:L1;
+    for idy=2:L2
+      if(str1(idx-1)==str2(idy-1))
+        score=m;
+      else
+        score=d;
+      end
+      m1=L(idx-1,idy-1) + score;
+      m2=L(idx-1,idy) + g;
+      m3=L(idx,idy-1) + g;
+      L(idx,idy)=min(m1,min(m2,m3));
+    end
+  end
+  
+  dist=L(L1,L2);
+endfunction