如何计算Ruby中哈希数组属性的不同值？

Question

我已经散列的数组称为@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" }] 

什么是计算user_name在@messages（应该在这里给3）不同值的方法？

Answer 1

没有方法做到这一点，我能想到的最简单的办法是使用地图：

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

您已经有了答案，但如果你也有兴趣在实际的每user_name，你可以做

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

然后counts.size告诉你有多少个不同的名字。

Answer 3

另一种方法是使用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