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MathGroup Archive 2007

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Re: Another question on lists

  • To: mathgroup at smc.vnet.net
  • Subject: [mg80671] Re: Another question on lists
  • From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
  • Date: Tue, 28 Aug 2007 02:19:21 -0400 (EDT)
  • Organization: The Open University, Milton Keynes, UK
  • References: <fatglk$2k6$1@smc.vnet.net>

Mauricio Esteban Cuak wrote:
> Hello again.Thank you very much for your previous help. However, I
> seem to stumble on another rock:
> 
> I  have a list of n sub-lists with different number of elements. I
> want to select the list with the highest number of elements.
> I tried to combine the Select function with Lenght but couldn't do it:
> 
> Select[list, Length /@ list >= Max[Length /@ list] &]

You were almost there: you must take the length of the current element 
(i.e. Length[#]) and compare it against the greatest length of of every 
element (Length /@ lst). For instance,

In[1]:= lst = {{1, 2, 3, 4}, {5, 6}, {7, 8, 9, 10}, {11, 12, 13}};
Select[lst, Length[#] == Max[Length /@ lst] & ]

Out[2]= {{1, 2, 3, 4}, {7, 8, 9, 10}}

<snip>

> P.D.: Any tips,websites, books, on how to learn some basic programming
> on Mathematica?
> I'm slowly beginning to read "The Mathematica Book"...should I just
> concentrate on that?

An excellent book to start learning programming Mathematica is, _An 
Introduction to Programming with Mathematica_, 3rd Edition, Paul R. 
Wellin, Richard J. Gaylord, and Samuel N. Kamin, Cambridge University 
Press,  (ISBN-13: 9780521846783 | ISBN-10: 0521846781). See

http://www.cambridge.org/catalogue/catalogue.asp?isbn=9780521846783

Table of Contents:
  1. An introduction to Mathematica;
  2. The Mathematica language;
  3. Lists;
  4. Functional programming;
  5. Procedural programming;
  6. Rule-based programming;
  7. Recursion;
  8. Numerics;
  9. Graphics programming;
10. Front-end programming;
11. Examples and applications;
12. Writing packages;
Appendix A: how expressions are evaluated;
Appendix B: debugging.

(Notebooks, code examples and solutions to some exercises, are available 
on the publisher web site. See the above link.)

About free resources, a good start would be to search MathSource (part 
of the Wolfram Library Archive) For instance, _Programming Paradigms via 
Mathematica (A First Course)_ may be of interest. See

http://library.wolfram.com/infocenter/MathSource/1847/

Hope this helps,
-- 
Jean-Marc



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