如何計算Ruby中哈希數組屬性的不同值？

Question

我已經散列的數組稱爲@messages：

[{ "id" => "1", "user_name" => "John", "content" => "xxxxx" }, 
{ "id" => "2", "user_name" => "John", "content" => "yyyyy" }, 
{ "id" => "3", "user_name" => "Paul", "content" => "zzzzzz" }, 
{ "id" => "4", "user_name" => "George", "content" => "xxyyzz" }] 

什麼是計算user_name在@messages（應該在這裏給3）不同值的方法？

Answer 1

沒有方法做到這一點，我能想到的最簡單的辦法是使用地圖：

attributes = [{ "id" => "1", "user_name" => "John", "content" => "xxxxx" }, 
    { "id" => "2", "user_name" => "John", "content" => "yyyyy" }, 
    { "id" => "3", "user_name" => "Paul", "content" => "zzzzzz" }, 
    { "id" => "4", "user_name" => "George", "content" => "xxyyzz" }] 

count = attributes.map { |hash| hash['user_name'] }.uniq.size 

Answer 2

您已經有了答案，但如果你也有興趣在實際的每user_name，你可以做

counts = attributes.inject(Hash.new{|h,k|h[k]=0}) { |counts, h| counts[h['user_name']] += 1 ; counts} 

然後counts.size告訴你有多少個不同的名字。

Answer 3

另一種方法是使用group_by：

attributes = [{ "id" => "1", "user_name" => "John", "content" => "xxxxx" }, 
    { "id" => "2", "user_name" => "John", "content" => "yyyyy" }, 
    { "id" => "3", "user_name" => "Paul", "content" => "zzzzzz" }, 
    { "id" => "4", "user_name" => "George", "content" => "xxyyzz" }] 
attributes.group_by{|hash| hash["user_name"]}.count # => 3