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>
- Length of a held expression