Re: Pattern to match a list of non-negative integers
- To: mathgroup at smc.vnet.net
- Subject: [mg108970] Re: Pattern to match a list of non-negative integers
- From: "Carl K. Woll" <carlw at wolfram.com>
- Date: Thu, 8 Apr 2010 08:04:09 -0400 (EDT)
On 4/7/2010 3:20 AM, 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[]?..
>
>
Yes. The named pattern must be the same, so only {1,1} would match.
Instead you can use PatternTest:
MatchQ[{1,2}, {_Integer?(#!=0&) .. }]
Of course, simpler is to use:
MatchQ[{1,2}, {__Integer?NonNegative}]
Carl Woll
Wolfram Research
> 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.
>
>