あれ、あまり速くならない

# -*- coding: utf-8 -*-
ref_file = "/Users/cherry/suitou.csv"
sums = {"01" => 0, "02" => 0, "03" => 0, "04" => 0, "05" => 0, "06" => 0,
"07" => 0, "08" => 0, "09" => 0, "10" => 0, "11" => 0, "12" => 0}
sougaku = 0

target_year = ARGV[0]
re_target_year = /^#{target_year}/

open("#{ref_file}") {|file|
while line = file.gets
if line =~ re_target_year
hairetsu = line.split(/,+/)
if hairetsu[0] =~ /\d\d\d\d\.(\d\d)\.\d\d/
month = $1
else
raise "日時の表記が不正です：#{line}"
end
sums[month] += hairetsu[1].to_i
end
end
}
sums.sort_by{|pair| pair[0].to_i}.each do |month, sum|
puts "#{target_year}年#{month}月の支出額 #{sum.to_s.rjust(6)} 円"
sougaku += sum
end

puts "------------------------------------------"
puts "#{target_year}年の支出総額 #{sougaku} 円"