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)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*Delivered-to*: l-mathgroup@wolfram.com*Delivered-to*: mathgroup-newout@smc.vnet.net*Delivered-to*: mathgroup-newsend@smc.vnet.net*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. >

**References**:**Find Position of many elements in a large list.***From:*benp84@gmail.com