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MathGroup Archive 2007

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Re: Custom sort a list of pairs

  • To: mathgroup at smc.vnet.net
  • Subject: [mg73690] Re: [mg73633] Custom sort a list of pairs
  • From: Bob Hanlon <hanlonr at cox.net>
  • Date: Sat, 24 Feb 2007 02:28:29 -0500 (EST)
  • Reply-to: hanlonr at cox.net

sortPairs[items_]:=Sort[Sort[data,#1[[2]]<#2[[2]]&],
      #1[[1]]>=#2[[1]]&];

sortPairs[{{1,a},{2,a},{3,a},{1,b},{2,b},{1,c}}]

{{3, a}, {2, a}, {2, b}, {1, a}, {1, b}, {1, c}}


Bob Hanlon

---- planetmarshalluk at hotmail.com wrote: 
> Hi there,
> 
> I've searched through existing posts to no avail, what I want to do is
> this:
> Sort a nested list of pairs, so that each pair is sorted by reverse
> canonical order on its first element, and in normal order on its
> second element.
> 
> For example, I want some function
> 
> sortPairs[items_]
> 
> that when given the input
> 
> {{ 1,a},{2,a},{3,a},{1,b},{2,b},{1,c}}
> 
> produces the output
> 
> {{3,a},{2,a},{2,b}{1,a},{1,b},{1,c}}
> 
> Any help much appreciated.
> 
> Thanks,
> Andrew



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