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Re: substitution within a substitution list

  • To: mathgroup at smc.vnet.net
  • Subject: [mg88592] Re: substitution within a substitution list
  • From: Bill Rowe <readnews at sbcglobal.net>
  • Date: Fri, 9 May 2008 03:25:24 -0400 (EDT)

On 5/8/08 at 4:13 AM, bipin.caz at googlemail.com (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}

>Does anyone know of a mathematica function for doing this?

Sure. Use a replacement rule with HoldPattern. For example,

In[4]:= subs /. HoldPattern[a_ -> _] -> a -> 20

Out[4]= {a->20,b->20,c->20}


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