Question

我的用户模型有一个带散列的元列，例如{“version”=＆gt;“1.0”，“country”=＆gt;“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所有可能的值......

我想我可以在一个大循环中完成它

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

但有更好的方法吗？

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]]

Answer 2

如果在sql DB中有序列化值，则只能使用此值来迭代它们。但是有几个NOSQL BD允许使用BD的工具（如mongo）迭代这些值

Answer 3

您可以对所有拥有元[＆＃39;国家＆＃39;] ==＆＃39;英国＆＃39;

的用户进行统计

User.all.inject{|count, u| count += 1 if u.meta['country'] == 'UK'}

Rails：计算哈希中键值的最佳实践

3 个答案: