在Ruby中，如何从哈希中提取具有该值的密钥 [英] in Ruby, how to extract a key from the Hash having the value

问题描述

 ＃拥有这个哈希值
哈希值= {'葡萄牙'=> 1，'France'=> 2，'USA'=> 3} 
 
＃country_id来自输入
 country_name =（hash.select {| k，v | v == country_id.to_i} .first || []）。first 
  

它能够正确提取国家名称，并且在国家/地区未找到时不会失败。

我对此很满意。

但是我的导师说可以/应该在可读性，长度和性能方面进行优化！ / p>

有什么可以比这更清晰/更快的？

请指教

您可以这样做：

b
$ b

  hash.invert [country_id.to_i]＃将适用于所有版本
  

或者，如@littlecegian所示

  hash.key（country_id.to_i ）＃只会在1.9 
  

或@steenslag

建议

  hash.index（country_id.to_i）＃将在1 .8和1.9，并在1.9 
  

上发出警告完整示例：

  hash = {'Portugal'=> 1，'France'=> 2，'USA'=> 3} 
 
％w [2 3 1 blah] .each do | country_id | 
 
＃所有版本
 country_name = hash.invert [country_id.to_i] 
 
＃1.9 only 
 country_name = hash.key（country_id.to_i） 
 
＃1.8和1.9，并在1.9 
 country_name = hash.index（country_id.to_i）
 
 
 printfcountry_id =％s ，country_name =％s\\\
，country_id，country_name 
结束
  

会打印：

  country_id = 2，country_name =法国
 country_id = 3，country_name =美国
 country_id = 1， country_name = Portugal 
 country_id = blah，country_name = 
  

看到它正在运行 here

i thought i'm a Ruby giant when i wrote this oneliner:

# 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

it does correctly extract the country name and does Not fail if country not found.

i'm totally pleased with it.

however my tutor says it can/should be optimized in terms of readability, length and performance!

what can be clearer/faster than this?

please advise

解决方案

well, seems your tutor is right :)

you can do like this:

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

or, as suggested by @littlecegian

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

or, as suggested by @steenslag

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

Full example:

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

will print:

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

see it running here

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