Services & Resources / Wolfram Forums / MathGroup Archive
-----

MathGroup Archive 2012

[Date Index] [Thread Index] [Author Index]

Search the Archive

Find Position of many elements in a large list.

  • To: mathgroup at smc.vnet.net
  • Subject: [mg127670] Find Position of many elements in a large list.
  • From: benp84 at gmail.com
  • Date: Tue, 14 Aug 2012 04:22:21 -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

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.



  • Prev by Date: Re: Simplify
  • Next by Date: How to use Pick[]; Is this a bug?
  • Previous by thread: Re: Drawing a Line From One Plot to Another
  • Next by thread: Re: Find Position of many elements in a large list.