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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;
> >
> > 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
>
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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