Rails:计算哈希中键值的最佳实践

Question

我有一个带有哈希的元列的用户模型,例如{"version"=>"1.0","country"=>"UK"}

在任何密钥中计算每个单独值的最佳实践/有效方法是什么？所以我可能想知道有多少记录有country = UK或USA或France等.我事先并不知道每个键中的所有可能值...

我想我可以在一个大循环中做到这一点

User.all.each do |user|
  user.meta["country"] ..........

但是有更好的方法吗？

Answer 1

是的,有 group_by

arr = [{"version" => "1.0", "country" => "UK"},
       {"version" => "1.0", "country" => "France"},
       {"version" => "1.0", "country" => "UK"},
       {"version" => "1.0", "country" => "USA"},
       {"version" => "1.0", "country" => "France"},
       {"version" => "1.0", "country" => "UK"}]
grouped = arr.group_by {|el| el["country"]}
#=> {"UK"=>[{"version"=>"1.0", "country"=>"UK"}, 
#           {"version"=>"1.0", "country"=>"UK"}, 
#           {"version"=>"1.0", "country"=>"UK"}], 
#    "France"=>[{"version"=>"1.0", "country"=>"France"}, 
#               {"version"=>"1.0", "country"=>"France"}], 
#    "USA"=>[{"version"=>"1.0", "country"=>"USA"}]}
grouped.map {|k,v| [k, v.length]}
# => [["UK", 3], ["France", 2], ["USA", 1]]