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Re: Pattern to match a list of non-negative integers

  • To: mathgroup at smc.vnet.net
  • Subject: [mg108942] Re: Pattern to match a list of non-negative integers
  • From: dh <dh at metrohm.com>
  • Date: Wed, 7 Apr 2010 07:27:20 -0400 (EDT)
  • References: <hphbnd$lj5$1@smc.vnet.net>

On 07.04.2010 09:20, Leo Alekseyev wrote:
> This seems like a very basic pattern-matching question, but somehow
> the answer eludes me at the moment.  I want to match a list of
> non-negative integers.  Something like MatchQ[{1,2},{(x_Integer /; x
>> = 0)..}] doesn't work -- do named patterns simply not play well with
> Repeated[]?..
>
> After starting to write this message, the following pattern, occurred to me:
> MatchQ[{2, 3}, x : {_Integer ..} /; ! MemberQ[x, y_ /; Negative[y]]]
> -- this works, but seems needlessly complex -- so I'll send the
> message on, in hopes that there is a cleaner way of writing the
> pattern.
>
Hi Leo,
if you repeat something like x_ .., you repeat the x, that is all the 
elements must be the same. Therefore, do not name the pattern. The 
following will work:
MatchQ[{1, 2}, {_ ?NonNegative ..}]

cheers, Daniel


-- 

Daniel Huber
Metrohm Ltd.
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CH-9100 Herisau
Tel. +41 71 353 8585, Fax +41 71 353 8907
E-Mail:<mailto:dh at metrohm.com>
Internet:<http://www.metrohm.com>



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