further refactoring to "Using a Ruby Class To Write Functional Code" - http://patshaughnessy.net/2014/4/8/using-a-ruby-class-to-write-functional-code

functional.rb

# Added: Line#to_s, #parse4, #parse5

class Line
 
  attr_reader :Line
 
  def initialize(text)
    @line = text
  end
 
  def office
    values[2].strip
  end
 
  def employee_id
    values[1].strip
  end
 
  def last_name
    name = values[0]
    name.split[0]
  end
 
  def to_s
    "employee_id: #{employee_id}\n" <<
    "office: #{office}\n" <<
    "last_name: #{last_name}"
  end
 
  private 
 
  def values
    @values ||= @line.split(',')
  end
end
 
def parse3(lines)
  lines.map do |text|
    Line.new(text)
  end.each do |line|
    puts "employee_id: #{line.employee_id}"
    puts "office: #{line.office}"
    puts "last_name: #{line.last_name}"
  end
end
 
# Tell, don't ask
def parse4(lines)
  lines.map do |text|
    Line.new(text)
  end.each do |line|
    puts line.to_s
  end
end
 
# A more functional approach - the input is going through a series of transformations 
# building the entire string at once (not recommended for large collections)
def parse5(lines)
  puts lines.map { |text| Line.new(text) }.join("\n")
end

For VERY_BIG_FILE.TXT I would do:

def parse6(lines)
  lines.each do |text|
    puts Line.new(text)
  end
end

File.open('VERY_BIG_FILE.TXT') do |f|
  parse6(f)
end