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

*To*: mathgroup at smc.vnet.net*Subject*: [mg100331] Re: [mg100289] Indexed Slot in a Rule - How to do it??*From*: Bob Hanlon <hanlonr at cox.net>*Date*: Mon, 1 Jun 2009 07:08:13 -0400 (EDT)*Reply-to*: hanlonr at cox.net

eqs = {0, 5*x1, 1, 10*x3, 3*x2}; Extract all variable names xvars = Union[Cases[eqs, _Symbol?(! NumericQ[#] &), Infinity]]; Attributes[Function] {HoldAll,Protected} Since Function has attribute HoldAll T = Function[Evaluate[xvars], Evaluate[eqs]]; The argument to T is a Sequence T[1, 2, 3] {0,5,1,30,6} T[Sequence @@ {1, 2, 3}] {0,5,1,30,6} Consequently, Apply T to a List T @@ {1, 2, 3} {0,5,1,30,6} Apply[T, {1, 2, 3}] {0,5,1,30,6} Bob Hanlon ---- Alan <alan.stone at yahoo.com> 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