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Clever way to manipulate lists

• To: mathgroup at smc.vnet.net
• Subject: [mg94366] Clever way to manipulate lists
• From: guerom00 <guerom00 at gmail.com>
• Date: Thu, 11 Dec 2008 03:45:28 -0500 (EST)

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 :)

• Follow-Ups:
  • RE: Clever way to manipulate lists
    • From: "Scot Martin" <smartin@seas.harvard.edu>
  • Re: Clever way to manipulate lists
    • From: DrMajorBob <btreat1@austin.rr.com>
  • Re: Clever way to manipulate lists
    • From: DrMajorBob <btreat1@austin.rr.com>
  • Re: Clever way to manipulate lists
    • From: Sseziwa Mukasa <mukasa@jeol.com>