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MathGroup Archive 1998

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Re: Importing external grid file to do contour plot

  • To: mathgroup at smc.vnet.net
  • Subject: [mg13047] Re: Importing external grid file to do contour plot
  • From: "P.J. Hinton" <paulh>
  • Date: Sat, 4 Jul 1998 16:44:51 -0400
  • Organization: Wolfram Research, Inc.
  • Sender: owner-wri-mathgroup at wolfram.com

On 30 Jun 1998, Sophie Hon wrote:

> I'm trying to read an outside grid file into Mathematica in order to do
> a contour plot.  It's a 50 by 50 grid, so that the data is arranged as
> 50 strings of 50 numbers.
> Here is what I have so far, which I know does not work:
> 
> ReadList["Macintosh HD:Mathematica 3.0 Files:fish:aqc.grd",
> Array[Number,{50,50}]]
> 
> I would appreciate your help very much. Sincerely,

How are the individual numbers separated in the file?  This is important
information to consider when formulating a ReadList[] expression.  If
you are dealing with space or tab delimited data, then the following
command should probably work:

	ReadList["Macintosh HD:Mathematica 3.0 Files:fish:aqc.grd",
                 Number,
                 RecordLists -> True
        ]

This tells Mathematica to read the contents of the file as a list.  By
default, spaces and tabs are interpreted by the kernel as separators
between numbers.  The option RecordLists, when set to true, starts a
new row in the List whenever a newline character is encountered.

A more detailed discussion of this can be found in the Mathematica book.
If you have access to the online documentation, you can evaluate the
following expression in a notebook and the HelpBrowser will be opened
to the appropriate section:

FrontEndExecute[FrontEnd`HelpBrowserLookup["MainBook", "2.11.7"]]

If you are dealing with comma delimited data, things are a little more
complicated.  See the FAQ at URL:

http://www.wolfram.com/support/InputOutput/ExternalFiles/CommaSeparatedData.html

for a possible solution.

--
P.J. Hinton
Mathematica Programming Group           paulh at wolfram.com Wolfram
Research, Inc.                  http://www.wolfram.com/~paulh/
Disclaimer: Opinions expressed herein are those of the author alone.



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