Re: Indexed Slot in a Rule - How to do it??

*To*: mathgroup at smc.vnet.net*Subject*: [mg100354] Re: Indexed Slot in a Rule - How to do it??*From*: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>*Date*: Mon, 1 Jun 2009 07:12:31 -0400 (EDT)*References*: <gvtme0$gct$1@smc.vnet.net>

Hi, a) is seems to be better to use x[1], x[2], ... instead of x1,x2,.. b) xvars={x1,x2,x3}; xvars /. sym_ /; StringMatchQ[ToString[sym], "x*"] :> Slot[ToExpression[StringDrop[ToString[sym], 1]]] Regards Jens Alan wrote: > Here's the problem. Convert a vector (list) with symbol names into > indexed slots. I'm doing this so that I can turn the vector into > function that takes a list. Here's an example of the desired > behavior: > > eqs = {0, 5*x1, 1, 10*x3, 3*x2}; > > convert this to: > > indexedeqs = {0, 5*#[[1]], 1, 10*#[[3]], 3*#[[2]]}; > > T[q_]:=indexedeqs; > > T[{1,2,3}] = {0,5,1,30,6} > > I can't for the life of me figure out how to do this. I've been > performing meta-Mathematica all week. Here's the closest I've come: > > xvars={x1,x2,x3}; > MapIndexed[Rule[#1, #[[First@#2]]] &, xvars] > > But, this treats the second # literally, and puts in the current item > from xvars. I need a way for the second # to just be # without it > really taking a value. > > So, I tried doing it as a string: > xvars={x1,x2,x3}; > MapIndexed[Rule[#1, "#[[" <> ToString[First@#2] <> "]]"] &, xvars] > > And this creates a rule that looks correct, but, its right hand side > of the rule is a string instead of an expression. > > I can't figure this out!!! Any help is greatly appreciated. > > All the best, > Alan >