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MathGroup Archive 2004

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Re: Sorting a list of pairs on the second elements

  • To: mathgroup at smc.vnet.net
  • Subject: [mg51379] Re: Sorting a list of pairs on the second elements
  • From: p-valko at tamu.edu (Peter Valko)
  • Date: Fri, 15 Oct 2004 02:47:42 -0400 (EDT)
  • References: <cklmi7$f1o$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

János,

Using a smaller example:

collectedDnaBin = {{"a", "2"}, {"b", "1"}};
ord[p1_, p2_] := OrderedQ[{p1[[2]], p2[[2]]}];
Sort[collectedDnaBin, ord]

will result in 
{{"b", "1"}, {"a", "2"}}



Regards (Udv)
Peter


János <janos.lobb at yale.edu> wrote in message news:<cklmi7$f1o$1 at smc.vnet.net>...
> Hi,
> 
> I have a list, for example
> In[101]:=
> collectedDnaBin
> 
> Out[101]=
> {{gggcggcgacctcgcgggttttcgctatttatgaaaattttccggtttaaggcgtttccgttcttcttcg 
> tcataa\
> cttaatgtttttatttaaaatacc,1},{\
> tatttttgtaattcaatactgcttcttcttgcctttgcggaatttggccttttaaaagtatttatcg,13}, 
> {\
> tatttttgtaattcaatactgcttcttcttgcctttgcggaatttggccttttaaa,12},{\
> tatttttgtaattcaatactgcttcttctt,11},{aaattttccggtttaaggcgtttccgttcttcttcg 
> tca,\
> 122},{aaattttccggtttaaggcgtttccgttctt,121},{ttcttgcctttgcgg,1211},{\
> actgcttcttcttgcctttgcggaatttg,1221},{\
> gctatttatgaaaattttccggtttaaggcgtttccgttcttcttcgtcataa,133},{
>     
> gctatttatgaaaattttccggtttaaggcg,132},{gctatttat,131},{gcggaatttggcctttta 
> aa,\
> 1321},{aaattttcc,13211},{aatactgcttcttcttgcctttgcggaatttggccttttaaaagt,1 
> 331},{
>      tgaaaattttccggttt,13311}}
> 
> It is a list of pair of Strings.  I would like to Sort it on the second  
> elements of the pairs.
> I can do the naive approach with:
> In[109]:=
> Map[Reverse,Sort[Map[Reverse,collectedDnaBin]]]
> 
> Out[109]=
> {{gggcggcgacctcgcgggttttcgctatttatgaaaattttccggtttaaggcgtttccgttcttcttcg 
> tcataa\
> cttaatgtttttatttaaaatacc,1},{tatttttgtaattcaatactgcttcttctt,11},{\
> tatttttgtaattcaatactgcttcttcttgcctttgcggaatttggccttttaaa,12},{
>      aaattttccggtttaaggcgtttccgttctt,121},{ttcttgcctttgcgg,1211},{\
> aaattttccggtttaaggcgtttccgttcttcttcgtca,122},{actgcttcttcttgcctttgcggaat 
> ttg,\
> 1221},{tatttttgtaattcaatactgcttcttcttgcctttgcggaatttggccttttaaaagtatttat 
> cg,13}\
> ,{gctatttat,131},{gctatttatgaaaattttccggtttaaggcg,132},{gcggaatttggccttt 
> taaa,\
> 1321},{aaattttcc,13211},{\
> gctatttatgaaaattttccggtttaaggcgtttccgttcttcttcgtcataa,133},{\
> aatactgcttcttcttgcctttgcggaatttggccttttaaaagt,1331},{tgaaaattttccggttt,1 
> 3311}}
> 
> and it does the job, but I am wondering if it can be done by  
> Sort[list,func] where func would tell Sort to do the sorting of the  
> pairs by the second elements.  I tried from Ted Érsek's excellent page  
> http://www.verbeia.com/mathematica/tips/HTMLLinks/Tricks_P-Z_22.html
> 
> Sort[collectedDnaBin,#1[[2]] < #2[[2]] &] but that does not want to do  
> the trick for me.  The Mapping of RoteteLeft and RotateRight, which is  
> a generalization of my naive approach above, he shows on the same page,  
> does it, but I do not know how to put that into Sort as second  
> argument.  Maybe I should not, but rather to write a mySort function  
> based upon his idea... ?
> 
> In general, if I have a list whose elements are m-member lists, like  
> {{a1,...,am},...,{z1,...,zm}}, then my question is what is the  
> best/fastest way to sort it on the k-th elements of the members where  
> 1<=k<=m and ak,...,zk are arbitrary objects - in my case Strings - and  
> use as little memory for it as possible.
> 
> 
> Thanks ahead,
> 
> János
> ----------------------------------------------
> Trying to argue with a politician is like lifting up the head of a  
> corpse.
> (S. Lem: His Master Voice)


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