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Re: Find Position of many elements in a large list.

  • To: mathgroup at smc.vnet.net
  • Subject: [mg127689] Re: Find Position of many elements in a large list.
  • From: Matthias Bode <lvsaba at hotmail.com>
  • Date: Wed, 15 Aug 2012 03:33:46 -0400 (EDT)
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  • References: <20120814082221.E17D66791@smc.vnet.net>

Hola:
INPUT:
list01 = {1, 2, 3, 4, 5, 5, 6, 7, 8, 9, 17}; list02 = {3, 5, 17}; Table[{list02[[n]], Position[list01,        list02[[n]]]}, {n, 3}]
OUTPUT:{{3, {{3}}}, {5, {{5}, {6}}}, {17, {{11}}}}
Atentamente,
MATTHIAS BODE
S 17.35775=B0, W 066.14577=B0
2'740 m
AMSL.




> From: benp84 at gmail.com
> Subject: Find Position of many elements in a large list.
> To: mathgroup at smc.vnet.net
> Date: Tue, 14 Aug 2012 04:22:21 -0400
>
> I have a sorted, 1-dimensional list X of 1,000,000 integers, and a sorted, 1-dimensional list Y of 10,000 integers.  Most, but not all , of the elements of Y are also elements of X.  I'd like to know the positions of the elements in X that are also in Y.  What's the fastest way to compute this?
>
> I have an algorithm in mind but it requires lots of custom code and I'm wondering if there's a clever way to do it with built-in functions.  Thanks.
>


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