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Re: replace one rule in a list of rules

  • To: mathgroup at smc.vnet.net
  • Subject: [mg125544] Re: replace one rule in a list of rules
  • From: Ray Koopman <koopman at sfu.ca>
  • Date: Sun, 18 Mar 2012 02:43:33 -0500 (EST)
  • Delivered-to: l-mathgroup@mail-archive0.wolfram.com
  • References: <jk1fv4$515$1@smc.vnet.net>

On Mar 17, 12:54 am, Kathryn Isaac <kathryn.is... at gmail.com> wrote:
> 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

If all you want to change is the right-hand side of the rule
then use RuleDelayed with a dummy right-hand-side variable:

rlist = {a -> a1, b :> bx};
bx = b1; {a,b}/.rlist
bx = b2; {a,b}/.rlist

{a1,b1}
{a1,b2}



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