Re: Passing arguments and pattern matching
- To: mathgroup at smc.vnet.net
- Subject: [mg33821] Re: [mg33792] Passing arguments and pattern matching
- From: Andrzej Kozlowski <andrzej at tuins.ac.jp>
- Date: Fri, 19 Apr 2002 02:27:41 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
The answer to your question seems indeed rather simple but it may be
that I have just missed yur point . Anyway it seems to me that the
following does what you are asking for(?):
In[1]:=
a = {x, Log[x], y, x y, Log[y] };
In[2]:=
b = {x};
In[3]:=
myPattern[lista_List,listb_List] := Position[lista,#]&/@listb
In[4]:=
myPattern[a,b]
Out[4]=
{{{1},{2,1},{4,1}}}
In[5]:=
myPattern[a,{Log[x]}]
Out[5]=
{{{2}}}
Andrzej Kozlowski
Toyama International University
JAPAN
http://platon.c.u-tokyo.ac.jp/andrzej/
On Tuesday, April 16, 2002, at 04:50 PM, Coleman, Mark wrote:
> Greetings,
>
> I have a question on pattern matching that I have been struggling with.
> First I'll describe the issue broadly, and then attempt to illustrate
> it with a specific example. My intution is that is a relatively simple
> answer, but I have been unable to find it.
>
> I would like to write a general function that accepts these two lists
> as arguments, i.e., myPattern[a_List,b_List]. The function would act
> something like the built-in Mathematica Postion[] pattern function and
> return the positions of any elements of b that occur in List a. This
> function will be called by other functions, so the user will not know
> in advance the values of lists a or b. In my attempts to build this
> function I have used the Position[] function. The difficulty is that
> Position treats the arguments I pass it as 'literal', and not as
> references to what the arguement represents.
>
> For instance, let's say I define two lists as follows:
>
> a = {x, Log[x], y, x y, Log[y] };
> b = {x};
>
> Now say I wish to compute the position of x or various functions of x
> in a, then of course
>
>
> In[24]:= Position[a,x]
>
> Out[24]= {{1},{2,1},{4,1}}
>
> In[26]:= Position[a,Log[x]]
>
> Out[26]= {{2}}
>
> and so on. But now assume I wish to define a function
>
> myPattern[lista_List,listb_List] := Position[lista,listsb]
>
> If I call myPatten[a,b], this is the same as executing
>
>
> In[27]:=Position[a,b]
>
> Out[27]= {}
>
> My question is, how do I have Mathematica treat the second argument not
> as a literal ("b"), but as representing a the value of the underlying
> argument? For instance
>
> myPattern[a,{Log[x]}] would return {{2}}
>
> Thanks!
>
>
>
>