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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: [mg51345] Re: Sorting a list of pairs on the second elements
  • From: "Jens-Peer Kuska" <kuska at informatik.uni-leipzig.de>
  • Date: Fri, 15 Oct 2004 02:45:37 -0400 (EDT)
  • Organization: Uni Leipzig
  • References: <cklmi7$f1o$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Hi,

Sort[collectedDnaBin, Last[#1] < Last[#2] &]

Regards

  Jens

"János" <janos.lobb at yale.edu> schrieb im Newsbeitrag 
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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