require 'csv'

def extract_key_price(row)
  brand, item, price_str, *_blah_blah_blah = row # FIXME: Reflect the actual csv structure here
  key = "#{brand} #{item}"
  price = price_str.to_f

  [key, price]
end

# Building the dictionary of minimum prices for "<brand> <item>" keys
min_price = Hash.new(2**32) # Any number that is greater than any item price goes here

CSV.foreach("<source_filename>") do |row| # FIXME: Put source filename here
  key, price = extract_key_price(row)
  min_price[key] = price if min_price[key] > price
end

# Main processing
File.open('<target_filename>', 'w') do |result| # FIXME: Put result filename here
  CSV.foreach("<source_filename>") do |row|     # FIXME: Put source filename here
    key, price = extract_key_price(row)
    result.puts(CSV.generate_line(row)) if min_price[key] == price
  end
end