From: christopher.j.meisenzahl@...
Date: 2003-01-28T23:06:50+09:00
Subject: Re: Questions from a Ruby Newbie (file io and data structures)...

David,

Thanks very much!

That looks very elegant, if somewhat advanced. Can you point me to docs for the 
Matrix class? I can�t find it in my pickaxe book.  :-(

How does a matrix/vector differ from an array?

Thanks again,
Christopher

 
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Subject: Re: Questions from a Ruby Newbie (file io and data structures)...
From: dblack@candle.superlink.net
Date: Tue, 28 Jan 2003 22:43:02 +0900
In-reply-to: 62951
Hi --

On Tue, 28 Jan 2003 christopher.j.meisenzahl@citicorp.com wrote:

> I would like to read in a tab (or comma) delimited text file one line or one
> item at a time. The input file might look like this:
>
> col1,col2,col3
> a,b,c
> d,e,f
> g,h
> j
>
> Note that there is not the same amount of data in each column. It could vary.
>
> What is the best way to read this in from a file? When I'm done I would like 
to
> have all the items in col1 in an array, all the items in col2 in an array, and
> so on.
>
> I'm sure this is a rudimentary task, but I would like to see the most elegant
> ways in which Ruby permits something like this to be done.
>
> Any other thoughts very much appreciated!

Here's a way to do this with the Matrix class.  (It assumes
that there are no commas other than the field separators.)

  require 'matrix'
  fh = File.open("filename","r")

  m = Matrix[ *
	Matrix[ *
	  fh.readlines.map {|l| l.chomp.split(',') }
	].column_vectors
      ]

The idea is to create a first matrix, based on the splitting of
lines on commas, and then to create a second matrix whose vectors
are the column vectors (i.e., rotated) of the first matrix.

This leaves you with a matrix, made up of Vectors, where each vector
is padded with nils if it's shorter than whatever the longest one is.
For your sample data:

  Matrix[Vector["col1", "a", "d", "g", "j"], Vector["col2", "b", "e",
  "h", nil], Vector["col3", "c", "f", nil, nil]]


David

-- 
David Alan Black
home: dblack@candle.superlink.net
work: blackdav@shu.edu
Web:  http://pirate.shu.edu/~blackdav

 
Christopher J. Meisenzahl CPS, CSTE
Senior Software Testing Consultant
Spherion
christopher.j.meisenzahl@citicorp.com