       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 = Function[list, Length[Unevaluated[list]], HoldFirst] @@ Hold[{b, 3}]

Out = 2,

Or

In = Block[{b}, Length @@ Hold[{b, 3}]]

Out = 2,

or even

In = Block[{b}, Length[{b, 3}]]

Out = 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
>
>

```

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