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Re: substitution within a substitution list

  • To: mathgroup at smc.vnet.net
  • Subject: [mg88604] Re: substitution within a substitution list
  • From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
  • Date: Fri, 9 May 2008 07:16:33 -0400 (EDT)
  • Organization: The Open University, Milton Keynes, UK
  • References: <fvudmu$ebg$1@smc.vnet.net>

Bipin wrote:

> I'm trying to find a way of changing the substitution values within a
> substitution list.
> 
> For example, if I have the following substitution list:-
> 
> subs = {a->1, b->2, c->2}
> 
> I want to programmatically replace the value associated with 'b' from
> 2 to 20, ie ending up with
> 
> subs = {a->1, b->20, c->2}

You could use a rule to change the rules:

     subs /. (b -> x_) -> b -> 20

For instance,

In[1]:= subs = {a -> 1, b -> 2, c -> 2}

Out[1]= {a -> 1, b -> 2, c -> 2}

In[2]:= subs = subs /. (b -> x_) -> b -> 20

Out[2]= {a -> 1, b -> 20, c -> 2}

Regards,
-- Jean-Marc


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