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Re: Clever way to manipulate lists

  • To: mathgroup at smc.vnet.net
  • Subject: [mg94430] Re: Clever way to manipulate lists
  • From: David Bailey <dave at removedbailey.co.uk>
  • Date: Fri, 12 Dec 2008 06:58:34 -0500 (EST)
  • References: <ghqjve$14i$1@smc.vnet.net>

guerom00 wrote:
> Hi everyone,
> 
> I'm still struggling through lists manipulation. I'll take a concrete
> example to illustrate my point.
> Let's say I have a first list, say coordinates on a regular grid :
> 
> list1={{x1,y1},{x2,y2},{x3,y3}...{xN,yN}}
> 
> This obviously has a Length of N. Now, let's say I have a second list.
> In this one, there are fewer than N elements, some points are
> missing... Let's say it misses a point at x2 :
> 
> list2 ={{x1,z1},{x3,z3},{x4,z4}...{xN,zN}}
> 
> Now, since those two lists are not of the same length, I cannot add
> them, substract them or something. But list2 is included in list1 (in
> the sense of set theory). Now, what I want to do is, in this example,
> remove the point {x2,y2} from list1 and then the two list will have
> the same length and I'll be able to manipulate them as I want.
> Right now, I do that with For loops (detect elements which are in
> list1 and not in list2 and delete them, etc...) and that works but it
> is not elegant.
> I'm looking for a concise, elegant way to do that if somebody sees
> what I mean...
> 
> Thanks in advance :)
> 
I apologize for my previous answer to your question - as I expect you 
will have realised, I mis-read your message!

David Bailey
http://www.dbaileyconsultancy.co.uk


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