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MathGroup Archive 2008

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How to do a negative pattern?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg90562] How to do a negative pattern?
  • From: Steven Siew <stevensiew2 at gmail.com>
  • Date: Sun, 13 Jul 2008 15:47:31 -0400 (EDT)

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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