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MathGroup Archive 2009

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Re: DeleteCases

  • To: mathgroup at smc.vnet.net
  • Subject: [mg98189] Re: DeleteCases
  • From: Simon <simonjtyler at gmail.com>
  • Date: Wed, 1 Apr 2009 06:00:13 -0500 (EST)
  • References: <gqsn69$3qp$1@smc.vnet.net>

Hi Filippo,
the examples you give can be covered by using a ReplaceRepeated...
the below examples will delete the second occurrence, but are simply
modified.

In[1]:= {{0,0,1,1},{0,0,2,2},{0,0,3,3},{1,1,0,0},{1,1,2,2},{1,1,3,3},
{2,2,0,0},{2,2,1,1},{2,2,3,3},{3,3,0,0},{3,3,1,1},{3,3,2,2}}//.{x___,
{a_,a_,b_,b_},y___,{b_,b_,a_,a_},z___}:>{x,{a,a,b,b},y,z}
Out[1]= {{0,0,1,1},{0,0,2,2},{0,0,3,3},{1,1,2,2},{1,1,3,3},{2,2,3,3}}
or
In[2]:= {{0,0,1,1},{0,0,2,2},{0,0,3,3},{1,1,0,0},{1,1,2,2},{1,1,3,3},
{2,2,0,0},{2,2,1,1},{2,2,3,3},{3,3,0,0},{3,3,1,1},{3,3,2,2}}//.
{x___,a_List,y___,b_List,z___}/;a==Reverse[b]:>{x,a,y,z}
Out[2]= {{0,0,1,1},{0,0,2,2},{0,0,3,3},{1,1,2,2},{1,1,3,3},{2,2,3,3}}

Simon

On Mar 31, 5:19 pm, Filippo Miatto <sottosupr... at gmail.com> wrote:
> Dear all,
> Given this example list:
>
> {{0, 0, 1, 1}, {0, 0, 2, 2}, {0, 0, 3, 3}, {1, 1, 0, 0}, {1, 1, 2, 2}, 
> {1, 1, 3, 3}, {2, 2, 0, 0}, {2, 2, 1, 1}, {2, 2, 3, 3}, {3, 3, 0, 0},  
> {3, 3, 1, 1}, {3, 3, 2, 2}}
>
> I need the elements {a,a,b,b} and {b,b,a,a} to be the same, i.e. i  
> want to delete one of the two occurrences from the list. (or all but  
> one if the condition is more complicated, say {a,b,c,d} and {b,a,c,d}  
> or {a,b,c,d} and {a,b,d,c})
> How can i do that? Can i use DeleteCases? if so, what conditional  
> should I use to compare different elements in the list?
> I tried without success for all the night.. (it's 6.15AM now!)
> Thank you,
>
> Filippo



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