[英]in Ruby, how to extract a key from the Hash having the value
當我寫這個oneliner時,我以為我是一個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
它確實正確提取國家名稱,如果找不到國家,則不會失敗。
我很滿意。
但是我的導師說它可以/應該在可讀性,長度和性能方面進行優化!
什么比這更清楚/更快?
請指教
好吧,看來你的導師是對的:)
你可以這樣做:
hash.invert[ country_id.to_i ] # will work on all versions
或者,正如@littlecegian所建議的那樣
hash.key( country_id.to_i ) # will work on 1.9 only
或者,正如@steenslag所建議的那樣
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
將打印:
country_id = 2, country_name = France
country_id = 3, country_name = USA
country_id = 1, country_name = Portugal
country_id = blah, country_name =
如果它是ruby 1.9.3,你可以使用hash.key(country_id.to_i)
hash = { 'Portugal' => 1, 'France' => 2, 'USA' => 3 }
puts hash.invert[3] # "USA"
hash = { 'Portugal' => 1, 'France' => 2, 'USA' => 3 }
hash.index(2) # => "France"
是Ruby 1.8.x的方式。 index
方法在1.9中已棄用,並被替換為key
方法。
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