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MathGroup Archive 1998

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Re: Re: Efficient way to merge lists--Programming help

  • To: mathgroup at smc.vnet.net
  • Subject: [mg12801] Re: Re: Efficient way to merge lists--Programming help
  • From: "Allan Hayes" <hay at haystack.demon.cc.uk>
  • Date: Fri, 12 Jun 1998 04:05:33 -0400
  • References: <6ll172$elg$1@dragonfly.wolfram.com>
  • Sender: owner-wri-mathgroup at wolfram.com

Carl Woll wrote in message <6ll172$elg$1 at dragonfly.wolfram.com>...
>Hi Daniel,
>
>As you said, we can now compare timings of different solutions. I gave a
>slightly different solution than yours, and it had an error. Also,
>after comparing my fixed solution with yours, I realized how to speed
>it up slightly. My tests show that the following solution is slightly
>faster than yours.
>
>repair[rough_, fine_] := Module[{f,g,result},
> f[{a_,b_,c_}] := g[a,b,_] = {a,b,c};
> f /@ fine;
> result = Apply[g, rough, {2}];
> g = List;
> result
>]
> ...................[cut] ...........

Carl,
It looks as if you need {1}instead of {2} in line 4. g still has to do a
lot of searching. The following variant is about twice as quick on my
tests (its important to limit the search by Position)

repair2[rough_, fine_] :=
Module[{f, r=rough},
   f[s:{a___,_}] :=
       r[[First[Position[r,{a,_},{1},1,Heads->False]]]] = s;
    f /@ fine;
    r
]

Other variants, like using positions in both lists don't seem to be of
much benefit.

Allan
------------------------------------------------------------- 
Allan Hayes
Training and Consulting
Leicester UK
http://www.haystack.demon.co.uk
hay at haystack.demon.co.uk
voice: +44 (0)116 271 4198
fax: +44(0)116 271 8642



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