Re: patterns

• To: mathgroup at smc.vnet.net
• Subject: [mg3744] Re: patterns
• From: gaylord at ux1.cso.uiuc.edu (richard j. gaylord)
• Date: Sun, 14 Apr 1996 03:01:30 -0400
• Organization: university of illinois
• Sender: owner-wri-mathgroup at wolfram.com

```In article <4kkth9\$7jl at dragonfly.wolfram.com>, ianc at wolfram.com (Ian
Collier) wrote:

> 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;
> >
> >
>
>
> 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
>

ian [and the others who have posted responses to this question]:

you've all apparently missed the point of what this person wants to do [i
think]. she wants ONLY Sin[theta]/r to be returned, not 2*Csc[theta]/(2*r)
as well.

i'd give the answer to this question, myself but there is too little room
in the margin to fit it in.

-fermat-

--
"if you're not programming functionally, then you're programming dysfunctionally"

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```

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