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Re: Fast way to select those elements from a list that are in another

  • To: mathgroup at smc.vnet.net
  • Subject: [mg87087] Re: Fast way to select those elements from a list that are in another
  • From: "Jean-Marc Gulliet" <jeanmarc.gulliet at gmail.com>
  • Date: Mon, 31 Mar 2008 02:05:51 -0500 (EST)
  • References: <frt574$sj8$1@smc.vnet.net> <47EFACC1.90909@gmail.com>

On Mon, Mar 31, 2008 at 2:40 AM, Andrew Moylan
<andrew.j.moylan at gmail.com> wrote:
> Unfortunately, Pick[a, Thread[a == b]] doesn't perform the same task. In
>  your example, s3 typically evaluates to Sequence[]. That's why s1===s2===s3
>  subsequently evaluates to true:
>
>  s1===s2===s3
>  >> SameQ[s1,s2,Sequence[]]
>  >> SameQ[s1,s2]
>  >> True
>
>  This brings up an interesting quirk: you can only use SameQ to verify that
>  two things are identical if you can be sure that none of them is Sequence[]!

<snip>

You are right, of  course. Sorry about my silly post! (I totally
missed the point).

Best regards.
-- 
Jean-Marc


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