index.m and rindex.m

[Bill Denney]

Here is a patch to eliminate code duplication and speed up index and 
rindex.m.

Bill

scripts/ChangeLog:

2006-10-30  Bill Denney  <address@hidden>
   * strings/index.m, strings/rindex.m: speed up these functions and 
remove code duplication
Index: index.m
===================================================================
RCS file: /cvs/octave/scripts/strings/index.m,v
retrieving revision 1.18
diff -u -r1.18 index.m
--- index.m     10 Oct 2006 16:10:31 -0000      1.18
+++ index.m     31 Oct 2006 04:55:37 -0000
@@ -1,4 +1,4 @@
-## Copyright (C) 1996 Kurt Hornik
+## Copyright (C) 1996, 2006 Kurt Hornik
 ##
 ## This file is part of Octave.
 ##
@@ -19,6 +19,7 @@
 
 ## -*- texinfo -*-
 ## @deftypefn {Function File} {} index (@var{s}, @var{t})
+## @deftypefnx {Function File} {} index (@var{s}, @var{t}, @var{direction})
 ## Return the position of the first occurrence of the string @var{t} in the
 ## string @var{s}, or 0 if no occurrence is found.  For example,
 ##
@@ -27,74 +28,101 @@
 ##      @result{} 4
 ## @end example
 ##
+## @var{direction} may be either "first" or "last" and you will be given
+## either the first or last element found.  rindex is index called with
+## the "last" direction.
+##
 ## @strong{Caution:}  This function does not work for arrays of strings.
+## @seealso{find,rindex}
 ## @end deftypefn
 
 ## Author: Kurt Hornik <address@hidden>
 ## Adapted-By: jwe
 
-function n = index (s, t)
+function n = index (s, t, direction)
 
   ## This is patterned after the AWK function of the same name.
 
-  if (nargin != 2)
+  if (nargin < 2) || (nargin > 3)
     print_usage ();
+  elseif (nargin < 3)
+    direction = "first";
   endif
-  
-  if (!ischar (s) || !ischar (t) || all (size (s) > 1) || all (size (t) > 1) )
+  direction = lower (direction);
+
+  if ! (ischar (s) && ischar (t) && isvector (s) && isvector (t) )
     error ("index: expecting string arguments");
+  elseif ! strcmp (direction, {"first" "last"})
+    error ("index: direction must be either \"first\" or \"last\"");
   endif
 
   l_s = length (s);
   l_t = length (t);
-  
+
+  n = 0;
   if ( l_s == 0 || l_s < l_t )
     ## zero length source, or target longer than source
+    ## return 0
     v = [];
-    
+
   elseif ( l_t == 0 )
     ## zero length target: return first
     v = 1;
-    
+
   elseif ( l_t == 1 )
     ## length one target: simple find
-    v = find (s==t);
-    
+    v = find (s==t, 1, direction);
+
   elseif ( l_t == 2 )
     ## length two target: find first at i and second at i+1
-    v = find (s (1 : l_s-1) == t (1) & s (2 : l_s) == t (2));
-    
+    v = find (s (1:l_s-1) == t(1) & s(2:l_s) == t(2), 1, direction);
+
   else
     ## length three or more: match the first three by find then go through
     ## the much smaller list to determine which of them are real matches
     limit = l_s - l_t + 1;
-    v = find (s (1 : limit) == t(1) & s (2 : limit+1) == t (2)
-             & s (3 : limit+2) == t(3) );
-  endif
-
-  if (l_t > 3)
-    
-    ## force strings to be both row vectors or both column vectors
-    if (all (size (s) != size (t)))
-      t = t.';
+    v = find (s (1:limit) == t(1)
+             & s (2:limit+1) == t(2)
+             & s (3:limit+2) == t(3));
+    if strcmp (direction, "last")
+      v = v(length(v):-1:1);
     endif
-    
-    ## search index vector for a match
-    ind = 0 : l_t - 1;
-    n = 0; # return 0 if loop terminates without finding any match
-    for idx = 1:length(v)
-      if (s (v(idx) + ind) == t)
-       n = v(idx);
-       break;
+
+    if (l_t > 3)
+
+      ## force strings to be both row vectors or both column vectors
+      if (all (size (s) != size (t)))
+       t = t.';
       endif
-    endfor
 
-  elseif (length(v) > 0)
-    n = v(1);
+      ## search index vector for a match
+      ind = 0:l_t-1;
+      ## return 0 if loop terminates without finding any match
+      for idx = 1:length(v)
+       if (s (v(idx) + ind) == t)
+         n = v(idx);
+         break;
+       endif
+      endfor
+    endif
 
-  else
-    n = 0;
+  endif
 
+  if (n == 0) && ~ isempty (v)
+    ## return the first found if n is not already set and v is not empty
+    n = v(1);
   endif
 
 endfunction
+
+## Test the function out
+%!assert(index("astringbstringcstring", "s"), 2)
+%!assert(index("astringbstringcstring", "st"), 2)
+%!assert(index("astringbstringcstring", "str"), 2)
+%!assert(index("astringbstringcstring", "string"), 2)
+
+## test everything out in reverse
+%!assert(index("astringbstringcstring", "s", "last"), 16)
+%!assert(index("astringbstringcstring", "st", "last"), 16)
+%!assert(index("astringbstringcstring", "str", "last"), 16)
+%!assert(index("astringbstringcstring", "string", "last"), 16)
Index: rindex.m
===================================================================
RCS file: /cvs/octave/scripts/strings/rindex.m,v
retrieving revision 1.16
diff -u -r1.16 rindex.m
--- rindex.m    10 Oct 2006 16:10:31 -0000      1.16
+++ rindex.m    31 Oct 2006 04:55:37 -0000
@@ -1,4 +1,4 @@
-## Copyright (C) 1996 Kurt Hornik
+## Copyright (C) 1996, 2006 Kurt Hornik
 ##
 ## This file is part of Octave.
 ##
@@ -28,6 +28,7 @@
 ## @end example
 ##
 ## @strong{Caution:}  This function does not work for arrays of strings.
+## @seealso{find,index}
 ## @end deftypefn
 
 ## Author: Kurt Hornik <address@hidden>
@@ -41,60 +42,6 @@
     print_usage ();
   endif
 
-  if (!ischar (s) || !ischar (t) || all (size (s) > 1) || all (size (t) > 1) )
-    error ("rindex: expecting string arguments");
-  endif
-
-  l_s = length (s);
-  l_t = length (t);
-
-  if ( l_s == 0 || l_s < l_t )
-    ## zero length source, or target longer than source
-    v = [];
-    
-  elseif ( l_t == 0 )
-    ## zero length target: return last
-    v = l_s;
-    
-  elseif ( l_t == 1 )
-    ## length one target: simple find
-    v = find (s==t);
-    
-  elseif ( l_t == 2 )
-    ## length two target: find first at i and second at i+1
-    v = find (s (1 : l_s-1) == t (1) & s (2 : l_s) == t (2));
-    
-  else
-    ## length three or more: match the first three by find then go through
-    ## the much smaller list to determine which of them are real matches
-    limit = l_s - l_t + 1;
-    v = find (s (1 : limit) == t(1) & s (2 : limit+1) == t (2)
-             & s (3 : limit+2) == t(3) );
-  endif
-
-  if (l_t > 3)
-    
-    ## force strings to be both row vectors or both column vectors
-    if (all (size (s) != size (t)))
-      t = t.';
-    endif
-    
-    ## search index vector for a match
-    ind = 0 : l_t - 1;
-    n = 0; # return 0 if loop terminates without finding any match
-    for idx = length(v):-1:1
-      if (s (v(idx) + ind) == t)
-       n = v(idx);
-       break;
-      endif
-    endfor
-
-  elseif (length(v) > 0)
-    n = v(length(v));
-
-  else
-    n = 0;
-
-  endif
+  n = index (s, t, "last");
 
 endfunction