ruby-on-rails - rails : best practice to count key values in hash

Question

我有一个用户模型，它有一个带有散列的元列，例如 {"version"=>"1.0", "country"=>"UK"}

计算任何键中每个单独值的最佳实践/有效方法是什么？所以我可能想弄清楚有多少记录有 country = UK 或 USA 或 France 等。我事先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]]