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