Re: How Do You Reduce Multiple Elements in a List?

• To: mathgroup at smc.vnet.net
• Subject: [mg33885] Re: How Do You Reduce Multiple Elements in a List?
• From: "Allan Hayes" <hay at haystack.demon.co.uk>
• Date: Sun, 21 Apr 2002 06:12:41 -0400 (EDT)
• References: <a9r3ve\$ltc\$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```Bob,

<<Statistics`DataManipulation`

data={1, 1, 1, 1, 1, 2, 2, 2, 4, 4, 4, 4, 4, 4};

Frequencies[data]

{{5,1},{3,2},{6,4}}

Or, own code:

{Length[#],First[#]}&/@Split[Sort[data]]

{{5,1},{3,2},{6,4}}

In this particular case Sort is not needed

{Length[#],First[#]}&/@Split[data]

{{5,1},{3,2},{6,4}}

--
Allan

---------------------
Allan Hayes
Mathematica Training and Consulting
Leicester UK
www.haystack.demon.co.uk
hay at haystack.demon.co.uk
Voice: +44 (0)116 271 4198
Fax: +44 (0)870 164 0565

"Bob Harris" <nitlion at mindspring.com> wrote in message
news:a9r3ve\$ltc\$1 at smc.vnet.net...
> Howdy,
>
> This seems like such a simple thing, yet I've search through the big book
> trying to figure it out.  Perhaps someone can help me...
>
> Given a list of integers that generally contains the same number many
times,
> I'd like to reduce it to a list that just gives me the number/count pairs.
> For example, I'd like to convert the list
>    {1, 1, 1, 1, 1, 2, 2, 2, 4, 4, 4, 4, 4, 4}
> into
>    {{1,5}, {2,3}, (4,6}}
>
> Is there a built-in function to do this?  Seems like a histogramming
> operation, but I get no useful matches from ?*Hist*.
>
> Thanks,
> Bob H
>
>

```

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