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MathGroup Archive 2004

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RE: selecting columns from a list

  • To: mathgroup at smc.vnet.net
  • Subject: [mg47876] RE: [mg47844] selecting columns from a list
  • From: David.Annetts at csiro.au
  • Date: Thu, 29 Apr 2004 03:06:03 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

Hi Edo,

> I just started with mathematica, wanted to load a comma 
> separated data 
> file and drop the first two columns. So I did
> data=Import["C:\Data\filename.ext","CSV"]; to get the file into a 
> variable "data", then I am stuck, after doing some reading in 
> the help 
> files about Drop, Partition, Take. ... etc
> could someone tell me what to read and where to find info 
> about indexing 
> different data structures

Both the online help (Part is the section you're after) and Ruskeepaa's
book are good places to start.

Given the commands to load the file ...

	SetDirectory["c:/tmpfiles"]
	csv = Import["2101.csv", "CSV"];

This reads data into an array.  We can get an element of this array
using
	line05col06 = csv[[5, 6]]

The first line is given by 
	l01 = csv[[1]] (or First[csv])

The first column, by
	c01 = #[[1]] & /@ csv

The 5th column by
	c05 = #[[5]] & /@ csv

We can take a combination using
	crd = Take[csv[[#]], {4, 6}] & /@ Range[Length@csv]
In the last case, I've taken columns 4, 5 & 6 from each line in the
file.

Regards,

Dave.
==========================================
  Dr. David Annetts
  EM Modelling Analyst
  CSIRO DEM            Tel: +612 9490 5416
  North Ryde           Fax: +612 9490 5467
  Australia         David.Annetts at csiro.au
===========================================


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