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MathGroup Archive 1999

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Re: Re: Re: Select in Math.

  • To: mathgroup at smc.vnet.net
  • Subject: [mg18663] Re: [mg18532] Re: [mg16518] Re: Select in Math.
  • From: kewjoi at hixnet.co.za (Kew Joinery)
  • Date: Thu, 15 Jul 1999 01:45:50 -0400
  • References: <ef280f77.24b8f8da@aol.com>
  • Sender: owner-wri-mathgroup at wolfram.com

There is a dispute between two professors and both sides asked me to be a witness,
so I will reproduce my original massage. Up to me (I'm only 17) the most seemly
code I received was from Andrzej Kozlowski and Jurgen Tischer:
  Select[Level[list,{-2}],OrderedQ]

BobHanlon at aol.com wrote:

> Arnold,
>
> As best as I can interpret the original question, I do not understand your
> result.  However, without a definition of the problem with more clarity than
> the one example, I can't say one way or the other.
>
> Perhaps, Eugene (kewjoi at hixnet.co.za) can clarify what the desired output
> should be.
>
> Bob Hanlon
>
> In a message dated 7/9/99 4:57:32 AM, arnoldk at gauss.cam.wits.ac.za writes:
>
> >Regarding your solution on extracting increasing sublists:
> >
> >[mg16518]. Consider
> >
> >In[42]:=
> >list={{1,4,3,2},{1,3,2,4},{2,3},{5},{6,8}};
> >
> >In[43]:=
> >list=Union[Sort /@ list]
> >
> >Out[43]=
> >{{5},{2,3},{6,8},{1,2,3,4}}
> >
> >In[44]:=
> >elts=Union[Flatten[%]]
> >
> >Out[44]=
> >{1,2,3,4,5,6,8}
> >
> >In[45]:=
> >incrlist=Select[list,Union[Flatten[Complement[list,{#}]]]!=elts&]
> >
> >Out[45]=
> >{{5},{6,8},{1,2,3,4}}
> >
> >However, the correct output should be  {{5},{2,3},{6,8}}.
> >
>
> Original messages:
>
> In a message dated 3/8/99 6:43:38 PM, kewjoi at hixnet.co.za writes:
>
> >My question is how can I extract (select) list of lists in increasing
> >order?
> >For example:
> >In[2]:=list={{{1,2,3,4},{1,2,4,3}},{{2,3,1},{5}},{6,7}}
> >Out[2]={{{1,2,3,4},{1,2,4,3}},{{2,3,1},{5}},{6,7}}
> >
> >I 'd like to obtain only the parts in increased order, therefore the
> >result should be :
> >Out[3]={{1,2,3,4},{5},{6,7}}
> >I did try (Cases, Select, and Extract) but definitely not in proper way.
> >
>
> Eugene,
>
> This may be what you want.
>
> list={{{1,2,3,4},{1,2,4,3}},{{2,3,1},{5}},{6,7}};
>
> The nesting of the lists does not appear to be pertinent to your problem,
> so simplify the structure by eliminating the nesting.  Also, Sort sublists
> and eliminate duplicates:
>
> list = Union[Sort /@ {list //.
>                                         {x__List} -> Sequence[x]}]
>
> {{5}, {6, 7}, {1, 2, 3}, {1, 2, 3, 4}}
>
> Eliminate subsets
>
> elements = Union[Flatten[list]];
>
> list = Select[list, Not[Union[Flatten[
>                                         Complement[list, {#}]]] == elements]&]
>
> {{5}, {6, 7}, {1, 2, 3, 4}}
>
> Sort by first element
>
> Sort[list, First[#1] < First[#2]&]
>
> {{1, 2, 3, 4}, {5}, {6, 7}}
>
> Bob Hanlon




Arnold Knopfmacher wrote:

> Bob
>
> As I understand Eugene's question (perhaps he can confirm this for us),
> if given the list
> list={{1,4,3,2},{1,3,2,4},{2,3},{5},{6,8}};
> the desired output would be {{2,3},{5},{6,8}} since these are the sublists
> whose elements are in increasing order. Your solution outputs
> {{5},{6,8},{1,2,3,4}}
> which would then be incorrect if my interpretation of the question is right.
> Arnold
>
> Arnold Knopfmacher
> Deputy Director:
> Centre for Applicable Analysis and Number Theory
> Witwatersrand University
> Johannesburg 2050
> South Africa
> http://sunsite.wits.ac.za/wits/science/number_theory/arnold.htm
> Fax: 2711-4039317
> Phone: 2711- 7163353
> email: arnoldk at gauss.cam.wits.ac.za


On Tue, Mar 9, 1999, Kew Joinery <kewjoi at hixnet.co.za> wrote:

>Hello,
>My name is Eugene(16 years old) and I ask you small help, please.
>My question is how can I extract (select) list of lists in increasing
>order?
>For example:
>In[2]:=list={{{1,2,3,4},{1,2,4,3}},{{2,3,1},{5}},{6,7}}
>Out[2]={{{1,2,3,4},{1,2,4,3}},{{2,3,1},{5}},{6,7}}
>
>I 'd like to obtain only the parts in increased order, therefore the
>result should be :
>Out[3]={{1,2,3,4},{5},{6,7}}
>I did try (Cases, Select, and Extract) but definitely not in proper way.





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