From: Chris Gernon <kabigon@...>
Date: 2006-10-27T23:00:53+09:00
Subject: Re: reading variables in a file

Ooo Grec wrote:
> I'm thinking of migrating from Fortran to Ruby. Do you think i should go ahead??

That entirely depends on what the application is, if you currently use a 
number of Fortran libraries, etc. However, I say it never hurts to learn 
another language (gives you another tool in your tool belt), and Ruby is 
one of the easiest to learn and most useful out there.

> First problem i have.
> How to read a file with several fields? This means:
> Imagine a file:
> Peter4 1990
> Sam 3 1980
> Grac6 1991

A typical Ruby program to do this would look something like this. This 
is pretty simple, so I combined reading from the file and writing to a 
new file into the same program. Also, the real "Ruby Way" to do this 
would be to create a Person class with name, order, and year attributes 
... but I figured a "quick and dirty" approach of storing the values in 
a hash would work for a simple example like this. (Note that # starts 
comments, except inside double quotes, where #{} inserts a variable or 
expression inside the double-quoted string). Hope this helps!

#!/usr/bin/env ruby -w

INPUT_FILE = 'data.txt'
OUTPUT_FILE = 'new_data.txt'

people = [] #empty array
File.open(INPUT_FILE) do |data| # open file for reading
  data.each do |line| # for each line ...
    # if line matches (text containing no digits, then 1 or more digits, 
then a space, then 4 digits)
    if line =~ /^(\D*)(\d+) (\d\d\d\d)$/
      person = {:name => $1.strip, :order => $2, :year => $3} # capture 
matched values in a hash
      people << person # add the person hash to the people array
    else
      puts "Read line that was not in expected format!"
    end
  end
end
puts "read #{INPUT_FILE} file" # puts: put string (print to stdout)
puts 'Data read:'
people.each do |person| # for each person hash in the people array ...
  puts "Name: #{person[:name]}, Order: #{person[:order]}, Year: 
#{person[:year]}"
end

File.open(OUTPUT_FILE, 'w') do |new_data| # open file for writing
  people.each do |person| # for each person hash in the people array ...
    new_data.puts "#{person[:name]} #{person[:order]} #{person[:year]}" 
# write string to file
  end
end

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