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From: Paul_Abrahams@MTS.cc.Wayne.edu
Newsgroups: comp.lang.icon
Subject: Using the ``map'' function
Message-ID: <315814@MTS.cc.Wayne.edu>
Date: 3 Apr 91 23:20:20 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Distribution: inet
Organization: The Internet
Lines: 36


 
In doing the index for my latest book, I need to sort the entries using a
nonstandard collating sequence.  I therefore need a ``keytrans'' function
that transforms a sorting key to a key that uses the correct collating
sequence.  Here's the obvious way to do it in Icon:
 
procedure keytrans(key)
   static collator
   initial {collator := ...} # printable chars in collating sequence order
   return map(key, collator, &ascii[33:128])
end
 
This is simple but slow since the map must be regenerated for each key.
Here's the other way:
 
procedure keytrans(key)
   static collator, lookup
   initial {
      collator := ...
      lookup = map(&ascii[33:128], collator, &ascii[33:128])
      }
   local c, retval
   retval := ""
   every c := !key do
      retval ||:= lookup[ord(c) - 31]
   return retval
end
 
This is inelegant but fast.
 
Is there any way I can have my cake and eat it too?  I wouldn't mind a small
loss in speed, but the difference here seems pretty big.
 
Paul Abrahams
Abrahams@mts.cc.wayne.edu