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Re: choose elements from list based on elements in different list

• To: mathgroup at smc.vnet.net
• Subject: [mg86886] Re: choose elements from list based on elements in different list
• From: "Dana DeLouis" <dana.del at gmail.com>
• Date: Tue, 25 Mar 2008 01:16:12 -0500 (EST)

"Claus" <clausenator at gmail.com> wrote in message
news:frqpnb$4vl$1 at smc.vnet.net...
> Hi,
> I'm trying to choose elements from list based on elements in different 
> list and I came up with the ideas listed below. It seems to me that 
> there are a few too many steps involved here, and I need to run this on 
> larger lists (~20000 entries).
> Are there ways to improve this?
> Thanks,
> Claus
> 
> Here is the mathematica code:
> 
> Reihe1={22,33,44,0,0,16,5,0,0,0}
> Reihe2={16,27,0,0,5,11,5,0,0,12}
> 
> {22, 33, 44, 0, 0, 16, 5, 0, 0, 0}
> 
> {16, 27, 0, 0, 5, 11, 5, 0, 0, 12}
> 
> (*Find out where in Reihe1 and in Reihe2 are Zeros and notZeros*)
> 
> Reihe1Is0 = Thread[Reihe1 == 0]
> Reihe1Not0 = Thread[Reihe1 != 0]
> Reihe2Is0 = Thread[Reihe2 == 0]
> Reihe2Not0 = Thread[Reihe2 != 0]
> 
> {False, False, False, True, True, False, False, True, True, True}
> 
> {True, True, True, False, False, True, True, False, False, False}
> 
> {False, False, True, True, False, False, False, True, True, False}
> 
> {True, True, False, False, True, True, True, False, False, True}
> 
> (*Select the values of Reihe1 and Reihe2 which are of interest
> 
> There are 4 Cases (not all of them calculated later) :
>  Case1 :  Reihe1 and Reihe2 are 0
>  Case2 :  Reihe1 and Reihe2 are NOT 0
>  Case3 : (Reihe2 is NOT 0) AND (Reihe1 is 0)
>  Case4 : (Reihe1 is NOT 0) AND (Reihe2 is 0)*)
> 
> PreCase3=Pick[Reihe2,Reihe1Is0]
> PreCase4=Pick[Reihe1,Reihe2Is0]
> 
> {0, 5, 0, 0, 12}
> 
> {44, 0, 0, 0}
> 
> Case3=Select[PreCase3,#>0&]
> Case4=Select[PreCase4,#>0&]
> 
> {5, 12}
> 
> {44}


Hi.  Just another option would be to combine the two lists into an
integer.(0,1,2,or 3)


Reihe1 = {22, 33, 44, 0, 0, 16, 5, 0, 0, 0};
Reihe2 = {16, 27, 0, 0, 5, 11, 5, 0, 0, 12};

ptn = 2*DiscreteDelta /@ Reihe1 + DiscreteDelta /@ Reihe2

{0, 0, 1, 3, 2, 0, 0, 3, 3, 2}

Pick[Reihe2, ptn, 2]

{5, 12}

Pick[Reihe1, ptn, 1]

{44}

-- 
HTH   :>)
Dana DeLouis
Mathematica 6
But reading 5.2 Help. :>(