string-variable-Set-snarl
- To: mathgroup at smc.vnet.net
- Subject: [mg22491] string-variable-Set-snarl
- From: James Fuite and Tania Nordli <jfuite at UAlberta.ca>
- Date: Sat, 4 Mar 2000 02:26:55 -0500 (EST)
- Organization: University of Alberta, Edmonton, Canada
- Sender: owner-wri-mathgroup at wolfram.com
Dear Advanced Mathematica Users,
The following is a short and perhaps trivial problem that has caused me
some frustration. I cannot write a program that allows me to change the
value of any given variable if given the name of the variable as a
string. What follows is an equivalent situation. Let
In[3]= {cow = Random[], emu = Random[], ant = Random[]}
Out[3]= {0.2, 0.3, 0.4}
. . . . some selection process . . . .
In[25]= animalname
Out[25]= cow
In[25]= Head[animalname]
Out[25]= String
Given a string, here "cow", corresponding to a variable, here cow, I
cannot clear or set a value for the variable itself. Of course I cannot
use Clear[cow] or cow = 2 because I do not know which variable will be
chosen, as represented by the variable animalname. My lame attempts
such as Clear[animalname] or ToExpression[animalname] = 2 only fail to
affect cow - it seems that I am caught trying to work on the wrong side
of the equals sign (Set)! My goal would be a line such as:
In[28]= ToExpression[animalname]
Out[28]= 2
which I think would imply that cow = 2 and has thus been affected. Who
can guide me from line 25 to line 28? What are the general
considerations?
Sincerely,
James J. Fuite.