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Re: Length of a held expression

  • To: mathgroup at smc.vnet.net
  • Subject: [mg96560] Re: Length of a held expression
  • From: dh <dh at metrohm.com>
  • Date: Mon, 16 Feb 2009 06:58:59 -0500 (EST)
  • References: <gn8jdj$7qa$1@smc.vnet.net>


Hi Nikolaus,

obviously, your problem is to in-activate "Sequence". This can be done 

by severals ways. The most natural seems using "Unevaluated":

Length[{Unevaluated[b], 3}]



hope this helps, Daniel



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

> 




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