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Re: basic pattern matching

  • To: mathgroup at smc.vnet.net
  • Subject: [mg114349] Re: basic pattern matching
  • From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
  • Date: Thu, 2 Dec 2010 05:36:50 -0500 (EST)

On 30 Nov 2010, at 12:22, Peter Pein wrote:

>
> In[3]:== Cases[x,a_.*x:>a]
> Out[3]== {}
> should have been {1} shouldn't it? If the pattern matches (see
> Out[2]) then with a_. ==== 1. (Bug or feature?)
>
> In[4]:== Cases[y+x,a_.*x:>a]
> Out[4]== {1}
> is OK.
>
> Any enlightenment is highly welcome,
> thanks in advance, Peter
>

I think this is just a matter of the level at which Cases is applied. Note that:

Cases[x, a_.*x :> a, {0}]

{1}

Andrzej Kozlowski



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