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Re: How to do a negative pattern?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg90582] Re: How to do a negative pattern?
  • From: "David Park" <djmpark at comcast.net>
  • Date: Mon, 14 Jul 2008 05:22:44 -0400 (EDT)
  • References: <g5dm6i$ht4$1@smc.vnet.net>

mylist = {{1, 1}, {1, 2}, {1, 3}, {2, 1}, {2, 2}, {2, 3}};

DeleteCases[mylist, Except[{_, 3}]]
{{1,3},{2,3}}

Cases[mylist, {_, 3}]
{{1,3},{2,3}}

-- 
David Park
djmpark at comcast.net
http://home.comcast.net/~djmpark/


"Steven Siew" <stevensiew2 at gmail.com> wrote in message 
news:g5dm6i$ht4$1 at smc.vnet.net...
>I have used the function DeleteCases which has the format
>
> DeleteCases[expr,pattern]
>
> However what I wanted is a negative pattern like
>
> DeleteCases[expr,negpattern]
>
> But I have no idea how to craft a negative pattern. Alternatively I
> suppose I could do with a DeleteCasesNot function. Something like
> this:
>
> $ cat file012.out
> Mathematica 5.2 for Students: Microsoft Windows Version
> Copyright 1988-2005 Wolfram Research, Inc.
>
> In[1]:=
> Out[1]= {stdout}
>
> In[2]:= (* Write your mathematica code below *)
>
> In[3]:= mylist={ {1,1},{1,2},{1,3},{2,1},{2,2},{2,3} }
>
> Out[3]= {{1, 1}, {1, 2}, {1, 3}, {2, 1}, {2, 2}, {2, 3}}
>
> In[4]:= myselectionA = DeleteCases[mylist,{_,1}]
>
> Out[4]= {{1, 2}, {1, 3}, {2, 2}, {2, 3}}
>
> In[5]:= myselectionB = DeleteCasesNot[mylist,{_,3}]
>
> Out[5]= {{1, 3}, {2, 3}}
>
> In[6]:= (* End of mathematica code *)
>
> In[7]:= Quit[];
>
>
> Does anyone has any idea how I could code up a DeleteCasesNot
> function?
> 



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