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Re: Length of a held expression

  • To: mathgroup at smc.vnet.net
  • Subject: [mg96543] Re: Length of a held expression
  • From: David Bailey <dave at removedbailey.co.uk>
  • Date: Mon, 16 Feb 2009 06:55:51 -0500 (EST)
  • References: <gn8jdj$7qa$1@smc.vnet.net>

Nikolaus Rath wrote:
> Hello,
> 
> How can I get the length of a list in a Hold[] expression? I.e. if
> 
>  b = Sequence[1,2];
> 
> then I want the length of {b,3} given as 2. But
> 
>  Length[{b,3}]
> 
> gives me the length after splicing in b (which is 4), while
> 
>  Length[Hold[{b,3}]]
> 
> gives me the length of the hold expression (which is 1).
> 
> 
> Anyone able to help?
> 
> 
> Best,
> 
>    -Nikolaus
> 
> --
>  =C2=BBTime flies like an arrow, fruit flies like a Banana.=C2=AB
> 
>   PGP fingerprint: 5B93 61F8 4EA2 E279 ABF6  02CF A9AD B7F8 AE4E 425C
> 
I think it would help to describe what you are trying to do at a 
slightly higher level, because Sequence does its thing even inside Hold 
- for example:

Hold[Sequence[1, 2]]

David Bailey
http://www.dbaileyconsultancy.co.uk


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