Re: function mySet[]
- To: mathgroup at smc.vnet.net
- Subject: [mg36122] Re: [mg36096] function mySet[]
- From: Andrzej Kozlowski <andrzej at lineone.net>
- Date: Thu, 22 Aug 2002 04:32:59 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
One simple approach is to use Module:
In[1]:=
a = { 1, 2, 3, 4, 5 };
In[2]:=
mySet[ s_String ] :=Module[{t=Symbol[s]},t={ 2, 3, 4, 5, 6 }]
In[3]:=
mySet[ SymbolName[ Unevaluated[a] ] ];
In[4]:=
a
Out[4]=
{1,2,3,4,5}
Note that "Unevaluated" is needed since SymbolName evaluates its input.
Andrzej Kozlowski
Toyama International University
JAPAN
On Wednesday, August 21, 2002, at 10:52 AM, Prof. Korvink wrote:
> I am struggling with a problem:
>
> I would like to have a function mySet[] that takes a string argument
> that is the correct string name of a "variable" and is able to
> make assignments to that variable. Naively:
>
> a = { 1, 2, 3, 4, 5 };
> mySet[ s_String ] :=
> Symbol[ s ] = { 2, 3, 4, 5, 6 }; (* ERRONEOUS! *)
> mySet[ SymbolName[ a ] ];
> a
>
> should give:
>
> { 2, 3, 4, 5, 6 }
>
> The problem is that Symbol[ s ] immediately evaluates to a List
> and I cannot for the love of anything generate an expression that
> evaluates to the actual unevaluated symbol.
> I have tried many variants with HoldAll and so on, with no luck,
> hopefully only out of ignorance.
>
> What sometimes works (but circumstances is erratic!) is to do a:
>
> mySet[ s_String ] :=
> Evaluate[ToExpression[StringJoin[s,"={2,3,4,5,6}"]]]
>
> I do not find this a clean way to do things. Can anyone offer some
> insight and perhaps a solution?
>
> Jan Korvink
>
>
>
>