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

• To: mathgroup at smc.vnet.net
• Subject: [mg86755] Re: choose elements from list based on elements in different list
• From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
• Date: Thu, 20 Mar 2008 02:54:30 -0500 (EST)
• Organization: Uni Leipzig
• References: <frqpnb\$4vl\$1@smc.vnet.net>
• Reply-to: kuska at informatik.uni-leipzig.de

```Hi,

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

try for "PreCase3"

Last /@ Select[Transpose[{Reihe1, Reihe2}], #[[1]] == 0 &]

and

First /@ Select[Transpose[{Reihe1, Reihe2}], #[[2]] == 0 &]

for "PreCase4"

Regards
Jens

Claus wrote:
> 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}
>

```

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