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MathGroup Archive 2004

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

  • To: mathgroup at smc.vnet.net
  • Subject: [mg51453] Re: Re: Sorting a list of pairs on the second elements
  • From: "Peltio" <peltio at twilight.zone>
  • Date: Sun, 17 Oct 2004 21:49:43 -0400 (EDT)
  • References: <cklmi7$f1o$1@smc.vnet.net> <200410150647.CAA05265@smc.vnet.net> <200410160820.EAA23720@smc.vnet.net> <ckt7a7$7as$1@smc.vnet.net>
  • Reply-to: "Peltio" <peltioNOSP at Mdespammed.com.invalid>
  • Sender: owner-wri-mathgroup at wolfram.com

"DrBob" wrote

>Both methods do the same thing at my machine,

They should not when the data is actually made of Strings.

    sss={{"ttcttgcctttgcgg","121"},...}
and not symbols and integers as in
    sss={{ttcttgcctttgcgg,121},...}

>and there's also a third method that may do better: [snip]
>    Reverse /@ Sort[Reverse /@ sss]

I had already tried that one but it was slower than

    Transpose@Reverse@Transpose@Sort@Transpose@Reverse@Transpose[
                 sss]

Mapping Reverse on every row of a long list is more time consuming than
tranposing the matrix and swapping its *two* long rows.
This is the side effect of working with an interpreted language, I guess.

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






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