Re: Need to reduce 2 lists so that only {x,y} pairs with same x remain

• To: mathgroup at smc.vnet.net
• Subject: [mg24459] Re: Need to reduce 2 lists so that only {x,y} pairs with same x remain
• From: Paul Abbott <paul at physics.uwa.edu.au>
• Date: Tue, 18 Jul 2000 00:59:03 -0400 (EDT)
• Organization: University of Western Australia
• References: <8jc73k\$dg3@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```In article <8jc73k\$dg3 at smc.vnet.net>, materialsscientist at my-deja.com
wrote:

> I have 2 lists of data:
>
> for example
> data1={{1,1},{1.5,1.5},{2,2},{3,3},{4,4},{5,5}}
>
> data2={{1,2},{2,3},{3,4},{4,5},{6,7},{7,8}}
>
>
> I want to do a point by point comparision, so I
> need to reduce both data1 and data2 so that
> common x data in the {x,y} pairs for each list
> remain.
>
> Thus the lists should look like this:
>
> data1={{1,1},{2,2},{3,3},{4,4}}
> data2={{1,2},{2,3},{3,4},{4,5}}
>
> What function(s) would to something like this?

data1={{1,1},{1.5,1.5},{2,2},{3,3},{4,4},{5,5}}

data2={{1,2},{2,3},{3,4},{4,5},{6,7},{7,8}}

You are basically after the Intersection of the (common x data) of two
sets. You can use the SameTest option:

SetOptions[Intersection, SameTest -> (#1[[1]] == #2[[1]] & )];

and then

{data1, data2} =
{Intersection[data1, data2], Intersection[data2, data1]}

Cheers,
Paul

--
Paul Abbott                                   Phone: +61-8-9380-2734
Department of Physics                           Fax: +61-8-9380-1014
The University of Western Australia
Nedlands WA  6907
AUSTRALIA                             http://physics.uwa.edu.au/~paul

```

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