Re: patterns
- To: mathgroup at smc.vnet.net
- Subject: [mg3734] Re: patterns
- From: ianc (Ian Collier)
- Date: Sun, 14 Apr 1996 02:59:46 -0400
- Organization: Wolfram Research, Inc.
- Sender: owner-wri-mathgroup at wolfram.com
In article <4ki9uv$9dm at dragonfly.wolfram.com>, Susan Rempe
<rempe at euclid.chem.washington.edu> wrote:
> I have a list of numbers and symbols.
> How can I collect all the members of the list
> which have a common denominator?
>
> ex. list={Sin[theta]/r, Cos[theta]/(r*s), 2*Csc[theta]/(2*r)}
>
> Say I want to collect all members of the list with r in the denominator;
>
> i.e. answer=Sin[theta]/r;
>
If you know exactly what the denominator you want to select is then the
folling will work:
In[19]:=
list={Sin[theta]/r, Cos[theta]/(r*s), 2*Csc[theta]/(2*r)}
Out[19]=
Sin[theta] Cos[theta] Csc[theta]
{----------, ----------, ----------}
r r s r
In[20]:=
?Select
Select[list, crit] picks out all elements ei of list for
which crit[ei] is True. Select[list, crit, n] picks out
the first n elements for which crit[ei] is True.
In[21]:=
Select[ list, Denominator[ # ]==r&]
Out[21]=
Sin[theta] Csc[theta]
{----------, ----------}
r r
You can use more sophisticated selction criteria if you wish.
I hope this helps.
--Ian
-----------------------------------------------------------
Ian Collier
Wolfram Research, Inc.
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tel:(217) 398-0700 fax:(217) 398-0747 ianc at wolfram.com
Wolfram Research Home Page: http://www.wolfram.com/
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