Previous variable affects "/."
- To: mathgroup@smc.vnet.net
- Subject: [mg11236] Previous variable affects "/."
- From: Vilis Nams <vnams@nsac.ns.ca>
- Date: Mon, 2 Mar 1998 23:11:33 -0500
- Organization: ISINet, Nova Scotia
I am using "/." to change expressions, as follows:
In[1]:
{1, 2}, {3, 4}, {5, 6}, {7, 8}}; In[2]:
/. {x_,
y_} -> {x}
Out[2]: {1}, {3}, {5}, {7}}
The results are expected.
But, if I now define x to be something already, e.g. In[3]: ;
Then, when I do the Replace, Mathematica uses my previously-defined x, as follows
:
In[4]:
/. {x_, y_} -> {x}
Out[4]: {7}, {7}, {7}, {7}}
I tried to even wrap it inside of a function, to have x as a local
variabe, as
in:
In[5]:[v_] :odule[{x, y}, v /. {x_, y_} -> {x}];
But, it still used the x defined previously: In[6]:[a]
Out[6]:ยป7}, {7}, {7}, {7}}
This is no problem when I'm just creating and using variables in one
session,
because I can remember which variables I created. But, I have such
Replace
statements sprinkled inside of functions that I defined. I cannot
remember all
the symbols I used in those definitions. Even worse, I may not get an
error
message - I just may get the wrong result without knowing it.
How can I use the Replace and x_, and make sure that previously-defined
variables don't influence the results?
--------------------
Vilis O. Nams
Dept of Biology, NSAC
Box 550, Truro, NS, Canada
vnams @ nsac.ns.ca
-------------------