ruby-on-rails - Rails Ruby 哈希数组按键合并为平均值

Question

我有一个 activerecord 方法可以找到一周的所有事件， myevents.map { |x| x.start_date.day => [x.title]}(start_date 是日期时间字段，title 是字符串)这给了我一个哈希数组；

    [{11=>["40"]}, {11=>["0"]}, {11=>["0"]}, {11=>[""]}, 
     {11=>["0"]}, {11=>["0"]}, {11=>["33"]}, {12=>["9"]}, 
     {11=>["34"]}, {11=>["29"]}, {11=>["8"]}, {11=>["31"]}, 
     {11=>["40"]}, {11=>["34"]}] 

我想映射这些值，所以我得到一个看起来像这样的数组；

[ {11=>[ average of values that occur on the 11th]}, 
  {12=>[average of values that occur on the 12th]} ]

但我不太确定如何获得它。

Answer 1

我会使用 group_by , inject和 map .

ar = [  
        {11=>["40"]}, {11=>["0"]}, {11=>["0"]}, {11=>[""]},
        {11=>["0"]}, {11=>["0"]}, {11=>["33"]}, {12=>["9"]},
        {11=>["34"]}, {11=>["29"]}, {11=>["8"]}, {11=>["31"]}, 
        {11=>["40"]}, {11=>["34"]}
     ]

# first grouping the inner hash keys like on 11,12,etc. In each iteration, 
# {11=>["40"]}, {11=>["0"]} are being passed to the block of `group_by`. Now
# `h.keys.first` gives 11 from `{11=>["40"]}` and 11 from `{11=>["0"]}` likewise.
ary = ar.group_by { |h| h.keys.first }.map do |k,v|
  { k => v.map { |h| h[k][0].to_i }.inject(:+) / v.size } 
end

ary # => [{11=>19}, {12=>9}]