Re: Intersection problem

• To: mathgroup at smc.vnet.net
• Subject: [mg125984] Re: Intersection problem
• From: Yi Wang <tririverwangyi at gmail.com>
• Date: Wed, 11 Apr 2012 18:18:45 -0400 (EDT)
• Delivered-to: l-mathgroup@mail-archive0.wolfram.com

```There should be many ways to do it. The question is to find a good one. The simplest I can think of is:

first = {{a, x}, {b, y}, {c, z}};
second = {b, c, d};
Select[first, MemberQ[second, #[[1]]] &]

There are also some more complicated realisations, such as

first[[#]] & /@
Flatten@Map[Position[Transpose[first][[1]], #] &, second]

Best,
Yi

On Tuesday, April 10, 2012 2:28:23 AM UTC-4, Cisco Lane wrote:
> I need to select out the elements of the first list whose first elements are contained in the second list. For example
>
> first list: {{a,x},{b,y},{c,z}}
>
> second list: {b,c,d}
>
> result: {{b,y},{c,z}}
>
> Is there a quick way to do this? Intersection, maybe somehow?

```

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