gistfile1.rb

# Run this file in the same directory as weather.dat 

class NOAAParser
  def initialize(file)
    # Reject all lines in file that don't begin with whitespace and integer
    @lines = IO.readlines(file).select { |line| line =~ /^\s+\d/ }
  end
  
  def day_with_lowest_temp_spread
    # Maybe this regexp could be cleaner?
    @days = @lines.collect { |line| /^\s+(\d+)\s+(\d+\*?)\s+(\d+\*?)/.match(line).to_a }
    # Iterate over days, and coerce in place each item in the area into an integer. 
    @days.each { |day| day.map! &:to_i }
    # Compare the temp spreads and return the lowest one.
    @days.min { |a,b| a[2]-a[3] <=> b[2]-b[3] }[1]
  end
end

puts NOAAParser.new('weather.dat').day_with_lowest_temp_spread