Re: position of sequence of numbers in list

• To: mathgroup at smc.vnet.net
• Subject: [mg107009] Re: [mg106976] position of sequence of numbers in list
• From: DrMajorBob <btreat1 at austin.rr.com>
• Date: Sun, 31 Jan 2010 05:58:47 -0500 (EST)
• References: <201001301212.HAA25132@smc.vnet.net>

```I had no idea this would work... but it does.

list = {1, 2, 3, 4, 5};
Position[list, Sequence[3, 4]]

{{3}}

My first thought was

list /. {before___, 3, 4, ___} :> 1 + Length@{before}

3

But the other is far simpler.

Bobby

On Sat, 30 Jan 2010 06:12:04 -0600, JB <jkerrb at gmail.com> wrote:

> Hi,
>
> What is the most efficient way to find the position of the beginning
> of a sequence of numbers from a list?
>
> I found a couple of ways:
>
> find 3,4 in list={1,2,3,4,5};
>
>  1.   pos=Intersection[Position[list,3],(Position[list,4])+1]
>
>  2.   pos=Position[Partition[list,2,1],{3,4}]
>
> Are there other ways to do this?
> What is the best way when dealing with large lists?
>
> Thanks,
> JB
>

--
DrMajorBob at yahoo.com

```

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