Re: Length of a held expression

*To*: mathgroup at smc.vnet.net*Subject*: [mg96559] Re: [mg96524] Length of a held expression*From*: Leonid Shifrin <lshifr at gmail.com>*Date*: Mon, 16 Feb 2009 06:58:48 -0500 (EST)*References*: <200902150823.DAA08017@smc.vnet.net>

Hi Nikolaus, In[1] = Function[list, Length[Unevaluated[list]], HoldFirst] @@ Hold[{b, 3}] Out[1] = 2, Or In[2] = Block[{b}, Length @@ Hold[{b, 3}]] Out[2] = 2, or even In[3] = Block[{b}, Length[{b, 3}]] Out[3] = 2 Regards, Leonid On Sun, Feb 15, 2009 at 12:23 AM, Nikolaus Rath <Nikolaus at rath.org> 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 > >

**References**:**Length of a held expression***From:*Nikolaus Rath <Nikolaus@rath.org>