Rails Ruby 哈希数组按键合并到平均值答案

【问题标题】：Rails Ruby array of hashes merged by key to average valueRails Ruby 哈希数组按键合并到平均值
【发布时间】：2014-03-12 20:36:40
【问题描述】：

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 是一个日期时间字段，title 是一个字符串）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。

【问题讨论】：

标签： ruby-on-rails ruby arrays hash

【解决方案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}]

【讨论】：

在 'h.keys.first' 中'first' 做了什么？
@raphael_turtle 先做p ar.group_by { |h| h.keys.first }，看看下一个map块在做什么。

【解决方案2】：

另一种方法：--

array = [  
        {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"]}
     ]

    array.each_with_object({}) { |hObj, newHash| hObj.each { |k,v| 
         (newHash[k] ||= []) << v.first.to_i } }.collect{|k,v| 
         {k => (v.inject(:+))/v.size}}

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

【讨论】：