Mathematica 9 is now available
Services & Resources / Wolfram Forums
-----
 /
MathGroup Archive
2001
*January
*February
*March
*April
*May
*June
*July
*August
*September
*October
*November
*December
*Archive Index
*Ask about this page
*Print this page
*Give us feedback
*Sign up for the Wolfram Insider

MathGroup Archive 2001

[Date Index] [Thread Index] [Author Index]

Search the Archive

Re:Sorting and Selecting in Multilevel Lists

  • To: mathgroup at smc.vnet.net
  • Subject: [mg31179] Re:Sorting and Selecting in Multilevel Lists
  • From: "Ersek, Ted R" <ErsekTR at navair.navy.mil>
  • Date: Tue, 16 Oct 2001 01:18:58 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

aes wanted to sort a list of ordered pairs according to the magnitude of
(x^2+y^2).
The following works well. 

In[1]:=
  data={{3,1},{1,2},{8,5},{3,2},{1,1}};
  Sort[data, First[#1]^2+Last[#1]^2<First[#2]^2+Last[#2]^2& ]

Out[2]=
  {{1,1},{1,2},{3,1},{3,2},{8,5}} 

 ----------------------------------------
Here First[] is the x value, and Last[] is the y value.
A general tip;  First[expr] is slightly faster than Part[expr,1].  Also
Last[expr] should be faster than anything else that does the same thing.

Regards,
Ted Ersek

Check Mathematica Tips, Tricks at
http://www.verbeia.com/mathematica/tips/Tricks.html



  • Prev by Date: Re: Plot-Function
  • Next by Date: Re: Plot-Function
  • Previous by thread: Two-dimensional input
  • Next by thread: Parallel Processing