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MathGroup Archive 2002

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Re: List processing

  • To: mathgroup at
  • Subject: [mg37239] Re: List processing
  • From: daiyanh at (Daitaro Hagihara)
  • Date: Fri, 18 Oct 2002 05:16:57 -0400 (EDT)
  • References: <aokbp7$afv$>
  • Sender: owner-wri-mathgroup at

In article <aokbp7$afv$1 at>, John Leary <leary at> 

>This problem can be solved by conventional programming, but I wonder if 
>there is an elegant Mathematica solution ?
>A list contains pairs of values, with each pair representing the lower and 
>upper edge of a sub-range.  Some of the sub-ranges partially overlap, some 
>fully overlap, others don't overlap at all.  The problem is to produce a 
>second list that contains the overall upper and lower edges of the 
>overlapping sub-ranges.
>A simple example :  {{100,200},{150,250},{120,270},{300,400}}  would result 
>in {{100,270},{300,400}}.
>In the real case, the input list has several hundred elements and the 
>output list typically has five elements.
>I have a working solution based on loops, but there must be a more elegant 
>one.  I would be very grateful for any suggestions.

Block[{data = {{100,200},{150,250},{120,270},
  data = Sort[data,#[[1]]<#2[[1]]&];

{{100, 270}, {300, 400}}

I haven't tested too extensively.  The so-called
"Mathematica way" is illustrated by the use of
Fold function to process data, without which you
must resort to conventional looping.


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