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MathGroup Archive 2006

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Re: Insulating data from code

  • To: mathgroup at smc.vnet.net
  • Subject: [mg66591] Re: Insulating data from code
  • From: Peter Pein <petsie at dordos.net>
  • Date: Sun, 21 May 2006 00:29:41 -0400 (EDT)
  • References: <e4ekai$9av$1@smc.vnet.net> <e4jtnn$d02$1@smc.vnet.net> <e4mn63$6o7$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Paul Abbott schrieb:
> In article <e4jtnn$d02$1 at smc.vnet.net>, Peter Pein <petsie at dordos.net> 
> wrote:
> 
>> Ray Koopman schrieb:
>>> >From time to time I've wanted to partition the first level of one
>>> list, say A, the same way that another list, say B, is partitioned.
>>> One way to do this is
>>>
>>> copyPartition[A_List, B_List] /; Length@A >= Length@Flatten@B :=
>>>                               Module[{i = 0}, Map[A[[++i]]&,B,{-1}]]
>>>
>>> But all the methods I've thought of have a pointer that functions
>>> something like i in the above code. I'd like to eliminate the pointer,
>>> because in the unlikely event that A contains an unevaluated symbol
>>> that is the same as the name of the pointer with $ appended -- e.g.,
>>> i$, if the pointer is i -- then in the returned list that symbol will
>>> have a numeric value assigned to it. Unique[i] doesn't help. The
>>> only solution I see is the probabilistic one of giving the pointer a
>>> strange (random?) name that hopefully would be very unlikely to show
>>> up as data. But that would be giving up. Does anyone have any ideas?
>>>
>> Hi Ray,
>>
>>   use Replace[]:
>>
>> A={a,b,c,d,e};
>> B={{1},{2,3},{{{4}},5}};
>>
>> Ap=B/.Thread[Flatten[B]\[Rule]A]
>> --> {{a},{b,c},{{{d}},e}}
> 
> No, that won't work. Try
> 
>   A={a,b,c,d,a};
>   B={{1},{2,1},{{{3}},2}};
> 
>   Ap=B/.Thread[Flatten[B] -> A]
> 
> You get
> 
>   {{a}, {b, a}, {{{d}}, b}}
> 
> whereas I think the OP wanted
> 
>   {{a}, {b, c}, {{{d}}, a}}
> 
> Cheers,
> Paul
> 
> _______________________________________________________________________
> Paul Abbott                                      Phone:  61 8 6488 2734
> School of Physics, M013                            Fax: +61 8 6488 1014
> The University of Western Australia         (CRICOS Provider No 00126G)    
> AUSTRALIA                               http://physics.uwa.edu.au/~paul
> 
Hi Paul,

  well, I recognized this and came to a solution similar to J. Siehler's:

A={a,{b,{c,{d,{e}}}},f};
B={x,{x},{{x,x},x},x};

cpStruct=ReplacePart[##,
         Sequence@@(Position[#,_,{-1},Heads->False]&/@{##})]&;

cpStruct[B,A]
--> {a,{b},{{c,d},e},f}

Peter


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