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Re: easier method for Flatten[Position[list2,x_x...??

• To: mathgroup at smc.vnet.net
• Subject: [mg94080] Re: easier method for Flatten[Position[list2,x_x...??
• From: Raffy <raffy at mac.com>
• Date: Thu, 4 Dec 2008 07:15:55 -0500 (EST)
• References: <gh0jlg$5mu$1@smc.vnet.net> <200812020540.AAA19072@smc.vnet.net>

On Dec 3, 2:42 am, Curtis Osterhoudt <c... at lanl.gov> wrote:
>   These methods based on the replacement list are very clever! I have long
> gotten used to the replacements notation, but didn't know it could be used
> like this.
>    I tried to see if there was any documentation provided with Mathematica
> (v. 7, here) illustrating anything like that. However, the only documentation I can find on Rule gives the shorthand right-arrow notation "->" and say
> s NOTHING about the Rule[lhs, rhs] possibility (I had to deduce that from the solutions posted here, and look at the FullForm of some replacements).  Can anyone point me to a spot in the documentation where an example using the "Rule[lhs, rhs]" notation is used or explained? If not, it would be a nice improvement in future versions.
>
>           Regards,
>                        C.O.
>
> On Monday 01 December 2008 22:40:27 Szabolcs Horv=C3=A1t wrote:
>
>
>
> > Van Der Burgt, Maarten wrote:
> > > Dear all,
>
> > > Below I have two lists.
>
> > > The elements x in list1 all appear again in the 2nd level of list2
> > > together with an associated parameter xP.
>
> > > I want to extract the xP as illustrated below.
>
> > > I have the feeling it can be done in an easier way.
>
> > > Does anyone have an idea how?
>
> > Like this:
>
> > In[1]:=
> > list1 = {a, b, b, e};
> > list2 = {{a, aP}, {b, bP}, {c, cP}, {d, dP}, {e, eP}, {f, fP}};
>
> > In[3]:= list1 /. Rule @@@ list2
> > Out[3]= {aP, bP, bP, eP}
>
> > > Thanks for your help,
>
> > > Maarten
>
> > > list1={a,b,b,e};
>
> > > list2={{a,aP},{b,bP},{c,cP},{d,dP},{e,eP},{f,fP}};
>
> > > pos = Flatten[Position[list2,x_List/;x[[1]]==#]&/@list1];
>
> > > list2[[pos,2]]
>
> > > Out-> {aP,bP,bP,eP}
>
> =2D-
> =========================
==
> =========================
==
> ========
> Curtis Osterhoudt
> cfo at remove_this.lanl.and_this.gov
> PGP Key ID: 0x4DCA2A10
> Please avoid sending me Word or PowerPoint attachments
> Seehttp://www.gnu.org/philosophy/no-word-attachments.html
> =========================
==
> =========================
==
> ========

a->b//FullForm

• References:
  • Re: easier method for Flatten[Position[list2,x_x...??
    • From: Szabolcs Horvát <szhorvat@gmail.com>