How Do You Reduce Multiple Elements in a List?

• To: mathgroup at smc.vnet.net
• Subject: [mg33863] How Do You Reduce Multiple Elements in a List?
• From: Bob Harris <nitlion at mindspring.com>
• Date: Sat, 20 Apr 2002 02:49:57 -0400 (EDT)
• Sender: owner-wri-mathgroup at wolfram.com

```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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