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MathGroup Archive 2006

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Re: List difference using patterns and substitutions.

  • To: mathgroup at smc.vnet.net
  • Subject: [mg71325] Re: [mg71306] List difference using patterns and substitutions.
  • From: Sseziwa Mukasa <mukasa at jeol.com>
  • Date: Wed, 15 Nov 2006 06:43:19 -0500 (EST)
  • References: <200611141006.FAA06710@smc.vnet.net>

On Nov 14, 2006, at 5:06 AM, Nacho wrote:

> Hello.
>
> I'm trying to figure how can I build a difference list from another
> using only patterns and rule substitutions.
>
> The idea is to get from a list, another, one element shorter, where
> each value is the substraction of two consecutive elements in the
> original list, that is, from {1,2,3,5,5} get {1,1,2,0}.
>
> I've been thinking about it for a while, and I know several methods
> using a more traditional programming style (with For, for example),  
> but
> I have no idea if it is possible to make it simple and fast with rule
> substitutions.
>
> Any idea?

This isn't the kind of problem I'd attempt with pattern matching.

Subtract[#2,#1]&@@@Partition[list,2,1]

gives you the result you want.

Regards,

Ssezi


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