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Re: Filtering a list of list for certain elements that are neighbours

  • To: mathgroup at smc.vnet.net
  • Subject: [mg88839] Re: [mg88834] Filtering a list of list for certain elements that are neighbours
  • From: Curtis Osterhoudt <cfo at lanl.gov>
  • Date: Mon, 19 May 2008 05:14:48 -0400 (EDT)
  • Organization: LANL
  • References: <200805181134.HAA23914@smc.vnet.net>
  • Reply-to: cfo at lanl.gov

Something along these lines might work (needs to be modified for sub-lists of 
different lengths, containing different symbols, etc.):



In[987]:= mylist = {{a, b, c}, {a, c, b}, {b, a, c}, {b, c, a}, {c, 
   a, b}, {c, b, a}}

Out[987]= {{a, b, c}, {a, c, b}, {b, a, c}, {b, c, a}, {c, a, b}, {c, 
  b, a}}

In[998]:= (MatchQ[#1, {a, _, b}] || 
    MatchQ[#1, {b, _, a}] & ) /@ mylist

Out[998]= {False, True, False, True, False, False}

In[999]:= Pick[mylist, %]

Out[999]= {{a, c, b}, {b, c, a}}

          Hope that helps!
                    C.O.


On Sunday 18 May 2008 05:34:18 Steven Siew wrote:
> I have a list of lists
>
> mylist={{a,b,c},{a,c,b},{b,a,c},{b,c,a},{c,a,b},{c,b,a}}
>
> I want to filter out all lists that have "a being a neighbor to b".
>
> I am looking for the following result.
>
> {{a,c,b},{b,c,a}}
>
>
> For this toy example, I can probably do it by hand but my real problem
> has 120 lists in a list. And I need to filter out various combination
> of letters like "s cannot be next to d" , "s cannot be next to j" , "c
> cannot be next to j" , "h cannot be next to d" and "h cannot be next
> to s".



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