Mathematica 9 is now available
Services & Resources / Wolfram Forums / MathGroup Archive
-----

MathGroup Archive 2009

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

Search the Archive

Re: Using Map or Thread over selected parts of nested lists

  • To: mathgroup at smc.vnet.net
  • Subject: [mg95914] Re: Using Map or Thread over selected parts of nested lists
  • From: dh <dh at metrohm.com>
  • Date: Thu, 29 Jan 2009 05:59:50 -0500 (EST)
  • References: <glpfhn$knq$1@smc.vnet.net>


Hi Paul,

use the following statement after setting "source":

source=Switch[source,

{_ ..},source,

$Canceled,{},

_,{source}

]

this will give a list, empty if Canceled is chosen.

hope this helps, Daniel



Paul Ellsmore wrote:

> Hi,

> 

>  

> 

> I am currently working with a trial version of Mathematica 7, particularly

> with an interest in building a graphical user interface. I don't have a

> great familiarity with Mathematica, but I am trying hard to get to grips

> with a Mathenatica-style of thinking, and the way lists can be manipulated

> in particular. I have two questions, answers to which would help me a lot:

> 

>  

> 

> 1)      My GUI allows the user to select some data files to work with. I use

> the code:

> 

>  

> 

> source = SystemDialogInput[FileOpen]

> 

>  

> 

> This returns the full path for each file selected by the user - very

> convenient and user-friendly. My problem is that "source" is returned as a

> string (ie an atom) if one file is selected, but a nested list if multiple

> files are selected. I have similar instances in many parts of my program

> where the user might be working with one list of data or multiple lists, and

> I think the same issue will arise. So I would like to know if there is a way

> of forcing (in this case) "source" to be returned as a nestedlist type, even

> if the length of that list is one?

> 

>  

> 

> 2)      I have data in the format:

> 

>  

> 

> List1={{header,header},{header,header},{header,header},{frequency1,

> complexnumber1},{frequency2, complexnumber2},{frequency3, complexnumber4}.}

> 

>  

> 

> On very many occasions I want to deal with :

> 

>  

> 

> List2={{frequency1, realpart1},{frequency2, realpart2},{frequency3,

> realpart4}.}

> 

>  

> 

> Or some other trivial transform of complexnumbern. I have been through the

> VirtualBook, and Documentation centre, and tried various forms of Map and

> Thread, but I cannot find a way of "mapping" or "threading" a function like

> Re[expr] over one element of part of a list, as in:

> 

>  

> 

> List2={{frequency1, Re[complexnumber1]},{frequency2,

> Re[complexnumber2]},{frequency3, Re[complexnumber4]}.}

> 

>  

> 

> If someone could give me a pointer to the correct syntax, I would be very

> grateful.

> 

>  

> 

> At present, I am getting the results I want by using Ifs and Do loops, to

> deconstruct and reconstruct my lists, but I feel that is the wrong way to

> approach things - I want to use Mathematica's strengths, not force it to use

> a C type approach, just because that's what I am comfortable with.

> 

>  

> 

> Any suggestions gratefully received,

> 

>  

> 

>  

> 

> Cheers in advance,

> 

>  

> 

> Paul.

> 

>  

> 

>  

> 

>  

> 

> Dr. Paul A. Ellsmore

> 

>  

> 

> Nanion Limited

> 

> Oxford Centre for Innovation

> 

> Mill Street

> 

> Oxford

> 

> United Kingdom

> 

> OX2 0JX

> 

>  

> 

> Tel: +44 (0) 1865 811175

> 

> Fax: +44 (0) 1865 248594




  • Prev by Date: Mathematica notebooks don't print or PDF well under Linux
  • Next by Date: Re: Using Map or Thread over selected parts of nested lists
  • Previous by thread: Re: Using Map or Thread over selected parts of nested lists
  • Next by thread: Re: Using Map or Thread over selected parts of nested lists