# csv_1.csv
H1,H2,H3
V11,V22,V33
V14,V25,V35

# csv_2.csv
H1,H4
V1a,V4b
V1c,V4d

H1,H2,H3,H4
V11,V22,V33,
V14,V25,V35,
V1a,,,V4b
V1c,,,V4d

require "csv"

module MergeCsv
  def self.run(csv_1_path, csv_2_path)
    csv_1 = CSV.read(csv_1_path, headers: true)
    csv_2 = CSV.read(csv_2_path, headers: true)
    puts merge(csv_1, csv_2)
  end

  def self.merge(csv_1, csv_2)
    headers = (csv_1.headers + csv_2.headers).uniq.sort

    hash_array = [csv_1, csv_2].flat_map &method(:csv_to_hash_array)

    CSV.generate do |merged_csv|
      merged_csv << headers

      hash_array.each do |row|
        merged_csv << row.values_at(*headers)
      end
    end
  end

  def self.csv_to_hash_array(csv)
    csv.to_a[1..-1].map do |row|
      Hash[csv.headers.zip(row)]
    end
  end
end

if(ARGV.length != 2)
  puts "Use: ruby merge_csv.rb <file_path_csv_1> <file_path_csv_2>"
  exit 1
end

puts MergeCsv.run(ARGV[0], ARGV[1])

listPart_A = CSV.read(csv_path_A, headers:true)

    listPart_B = CSV.read(csv_path_B, headers:true)

    listPart_C = CSV.read(csv_path_C, headers:true)

    list = merge(listPart_A,listPart_B,listPart_C)

def merge(*csvs)
    headers = csvs.map {|csv| csv.headers }.flatten.compact.uniq.sort
    csvs.flat_map(&method(:csv_to_hash_array))
end

def csv_to_hash_array(csv)
    csv.to_a[1..-1].map do |row|
      Hash[csv.headers.zip(row)]
    end
end