Re: Extract values and multilpicities from list

• To: mathgroup at smc.vnet.net
• Subject: [mg64859] Re: Extract values and multilpicities from list
• From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
• Date: Mon, 6 Mar 2006 05:01:01 -0500 (EST)
• Organization: The Open University, Milton Keynes, UK
• References: <due96k\$ach\$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```Dr. Wolfgang Hintze wrote:
> Given a list of integers which may repeat, e.g.
>
> lstIn = {2,3,4,4,2,1,1,5,4}
>
> provide a list of different values and their respective multiplicities,
> in the example,
>
> LstOut= {{1,2},{2,2},{3,1},{4,3},{5,1}}
>
> Who finds the shortest function doing this task in general?
>
> Thanks.
>
> Best regards,
> Wolfgang
>
Hi Wolfgang,

What about the following one liner?

In[1]:=
lstIn = {2, 3, 4, 4, 2, 1, 1, 5, 4};

In[2]:=
{Flatten /@ ({Union[#1], Length[#1]} & ) /@
Split[Sort[lstIn]]}]

Out[2]=
{{1, 2}, {2, 2}, {3, 1}, {4, 3}, {5, 1}}

Best regards,
/J.M.

```

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