在Ruby中,如何从具有该值的Hash中提取密钥

Question

当我写这个oneliner时,我以为我是一个Ruby巨人:

# having this hash
hash = { 'Portugal' => 1, 'France' => 2, 'USA' => 3 }

# country_id comes from input
country_name = (hash.select { |k,v| v == country_id.to_i }.first || []).first

它确实正确提取国家名称,如果找不到国家,则不会失败.

我很满意.

但是我的导师说它可以/应该在可读性,长度和性能方面进行优化!

什么比这更清楚/更快？

请指教

Answer 1

好吧,看来你的导师是对的:)

你可以这样做:

hash.invert[ country_id.to_i ] # will work on all versions

或者,正如@littlecegian所建议的那样

hash.key( country_id.to_i )    # will work on 1.9 only

或者,正如@steenslag所建议的那样

hash.index( country_id.to_i )  # will work on 1.8 and 1.9, with a warning on 1.9

完整示例:

hash = { 'Portugal' => 1, 'France' => 2, 'USA' => 3 }

%w[2 3 1 blah].each do |country_id|

  # all versions
  country_name = hash.invert[ country_id.to_i ]

  # 1.9 only
  country_name = hash.key( country_id.to_i )

  # 1.8 and 1.9, with a warning on 1.9
  country_name = hash.index( country_id.to_i )


  printf "country_id = %s, country_name = %s\n", country_id, country_name
end

将打印:

country_id = 2, country_name = France
country_id = 3, country_name = USA
country_id = 1, country_name = Portugal
country_id = blah, country_name =

看到它在这里运行

Answer 2

如果它是ruby 1.9.3,你可以使用hash.key(country_id.to_i)

Answer 3

hash = { 'Portugal' => 1, 'France' => 2, 'USA' => 3 }
puts hash.invert[3] # "USA"