Re: Applying a set of rules to a List
- To: mathgroup at yoda.physics.unc.edu
- Subject: Re: Applying a set of rules to a List
- From: John Lee <lee at math.washington.edu>
- Date: Wed, 27 Jan 93 10:28:42 -0800
Tony Varghese <avarg at s1.arc.umn.edu> writes: > I would like to apply a set of rules to all the elements of a list and > I've tried a number of things with no success. > What I have is a set of equations in which certain variables are to be > held at fixed values. The equations are stored as a list, say, oldEqns. > The substitution rules are stored in a variable called fpRules. > I need to get a new set of equations obtained by ReplaceAll'ing the > old eqns with the fpRules. Here is one attempt: > applyRules[item_] := ReplaceAll[item, fpRules] > newEqns = Map[ applyRules, oldEqns ] > Unfortunately this did not work; I don't see any difference between > oldEqns and newEqns even though I KNOW there are places where the rules > can be applied. > Anyone see the problem? Your setup should work as it stands. Here's a simple example: In[89]:= oldEqns = {a,b,c,d} Out[89]= {a, b, c, d} In[90]:= fpRules = {a->A, c->C} Out[90]= {a -> A, c -> C} In[91]:= applyRules[item_] := ReplaceAll[item, fpRules] In[92]:= newEqns = Map[ applyRules, oldEqns ] Out[92]= {A, b, C, d} So my guess is that your rules aren't really doing what you want them to. Perhaps the left-hand sides don't really match the internal form (FullForm) of your equations. Jack Lee Dept. of Mathematics University of Washington Seattle, WA