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Re: Re: Sorting a list of pairs on the second elements

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  • Subject: [mg51412] Re: [mg51372] Re: Sorting a list of pairs on the second elements
  • From: János <janos.lobb at>
  • Date: Sat, 16 Oct 2004 04:20:51 -0400 (EDT)
  • References: <cklmi7$f1o$> <>
  • Sender: owner-wri-mathgroup at

On Oct 15, 2004, at 2:47 AM, Peltio wrote:

> "János" wrote
>>    Map[Reverse,Sort[Map[Reverse,collectedDnaBin]]]
>>    Sort[collectedDnaBin,#1[[2]] < #2[[2]] &]
>> but that does not want to do the trick for me.
> I wonder why. It should work, albeit inefficently. Mmmmm, have you  
> tried
> with parenthesis wrapped around the pure function?
>     Sort[collectedDnaBin,(#1[[2]] < #2[[2]])&]
> Have you tried it in a fresh kernel?

Yes, and yes.  It does not work.
Sort[sss, (Last[#1] < Last[#2] )&]


Maybe because they are Strings ?  I am just guessing...
>> 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.
> Dunno for the general case, but this -very inelegant - approach to sort
> according to the last element seems to be pretty fast (lots of  
> procedures
> but applied to the data as a whole, without timeconsuming mapping on  
> every
> single element)
>     Transpose@Reverse@Transpose@Sort@Transpose@Reverse@Transpose[
> collectedDnaBin ]

This one works fine.

> ( The first and last three procs just implement a swap function
>     swap[list_]:=Transpose@Reverse@Transpose[list]
> )
> The group's gurus will certainly find a proc at least ten times faster  
> than
> this, I'm sure.

I don't know.  The suggestions I got via the list and private are all  
excellent, but the data I had to sort got so big that I even did not  
get to that point to able to sort because the Kernel just quitted on me  
half way.  Now I am on a different "war-path" to get the results I need  
:)  /My secret prayers go out for a real 64-bit, or MORE, Mathematica  
on OSX..../

Thanks a lot,

> cheers,
> Peltio
> Invalid address in reply-to. Crafty demunging required to mail me.

I tried to employ Mathematica in "Crafty demunging" but I failed, so I  
send it "as is".  Now I embrace for an "Addressee not found..."  
thunder... :)

János Löbb
Yale University School of Medicine
Department of Pathology
Phone: 203-737-5204
Fax:      203-785-7303
E-mail: janos.lobb at

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