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MathGroup Archive 2012

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Re: replace one rule in a list of rules

  • To: mathgroup at smc.vnet.net
  • Subject: [mg125556] Re: replace one rule in a list of rules
  • From: Peter Pein <petsie at dordos.net>
  • Date: Sun, 18 Mar 2012 02:47:44 -0500 (EST)
  • Delivered-to: l-mathgroup@mail-archive0.wolfram.com
  • References: <jk1fv4$515$1@smc.vnet.net>

Am 17.03.2012 08:54, schrieb Kathryn Isaac:
> I have a list of simple rules. I want to repeatedly replace one of
> them.  Is the best way to simply prepend the new rules, or is there a
> "prettier" approach?
>
> Thanks,
> Alan Isaac
>

You can apply pattern matching to rules:

In[12]:= rules = Thread[{a,b,c} -> {x,y,z}]
Out[12]= {a -> x, b -> y, c -> z}
In[13]:= newrules = rules /. HoldPattern[b -> _] :> b -> newy
Out[13]= {a -> x, b -> newy, c -> z}



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