如果它们的第一个值相同，如何有条件地计算多维数组中的平均值

Question

我有一个包含如下值和数组的数组：

arr = [ 
        [ 0, [ [22,3],[23,5] ] ],
        [ 0, [ [22,1],[23,2] ] ],
        [ 1, [ [22,4],[23,4] ] ],
        [ 1, [ [22,2],[23,4] ] ]
      ]

我想根据前两个元素计算平均值，并希望在散列或数组中得到一个结果集，如下所示：

result = {
          22 => [(3+1)/2, (4+2)/2], 
          23 => [(5+2)/2, (4+4)/2] 
         }

例如：

key 是 22，value 是一个数组，其中包含按第一个元素 [=35] 分组的输入数组中第三个元素的平均值=]3 and 1, 4 and 2 并按第一个元素排序 0 and 1

数组是如何创建的

也许提及我的逻辑可能会有所帮助。

通过以下代码从我的 ActiveRecord 对象中获取数组：

arr = u.feedbacks.map{|f| [f.week, 
                           f.answers.map{|a|  [a.question.id, a.name.to_i]}]}

模型关联如下：

feedback belongs_to :user
feedback has_and_belongs_to_many :answers
answer belongs_to :question

对于每个问题，我想创建一个数组，其中包含按反馈周分组的平均答案。

Answer 1

如果是我，我可以随心所欲，我会重构 arr 的创建方式，因为

数组的维数是违反直觉的
转换再次付出代价，影响可读性，进而影响可维护性。

但我没有比从您显示的代码中看到的更多见解。所以，我试了一下，也许下面的代码就是你想要的？

totals = {}

arr.each do |row|
    index, answers = row

    answers.each do |answer|
        question, count = answer
        totals[question] ||= []
        totals[question][index] ||= []
        totals[question][index] << count
    end
end

下面是 totals 的输出结果，到那时获得平均值就很简单了。

{
    22 =>[[3, 1], [4, 2]], 
    23=>[[5, 2], [4, 4]]
}

EDIT 以下是我使用从@Humza

那里学到的 each_with_object 得出的解决方案

arr = [ 
    [ 0, [ [22,3],[23,5] ] ],
    [ 0, [ [22,1],[23,2] ] ],
    [ 1, [ [22,4],[23,4] ] ],
    [ 1, [ [22,2],[23,4] ] ]
]

result = arr.each_with_object({}) do |(index, feedbacks), totals|
    feedbacks.each do |(question, count)|
        totals[question] ||= {}
        totals[question][index] ||= []
        totals[question][index] << count
    end
    totals
end.each_with_object({}) do |(question, totals), result|
    result[question] = totals.map do |(index, total)|
        total.reduce(:+).fdiv(total.length)
    end
end

puts result.inspect
## Output 
# {22=>[2.0, 3.0], 23=>[3.5, 4.0]}

Answer 2

经过一些调试，以下应该有助于更快地获得结果：

Answer.
joins(:question, :feedbacks). # assuming that answer has_many feedbacks
group(["questions.id", "feedbacks.week"]). # assuming week is integer column
average("CAST(answers.name AS INT)"). # assuming that name is string-y column
each_with_object({}) do |(keys, average), hash|
  question_id, week = keys
  hash[question_id] ||= []
  hash[question_id][week] = average
end

如果您想保持原样（不建议），那么一个有效（尽管难以遵循）的解决方案是：

arr = [ 
  [0, [[22, 3], [23, 5]]],
  [0, [[22, 1], [23, 2]]],
  [1, [[22, 4], [23, 4]]],
  [1, [[22, 2], [23, 4]]]
]

arr.each_with_object({}) do |(a, b), hash|
  c, d, e, f = b.flatten
  # for first row this will be c, d, e, f = 22, 3, 23, 5

  hash[c] ||= []
  hash[c][a] ||= []
  hash[c][a] << d

  hash[e] ||= []
  hash[e][a] ||= []
  hash[e][a] << f


end.each_with_object({}) do |(k, v), hash|
  # k are your 'keys' like 22, 23
  # v is an array of arrays that you want to find out the averages of

  hash[k] = \
    v.map do |array|
      array.reduce(:+).fdiv(array.size)
    end
end

如果它们的第一个值相同，如何有条件地计算多维数组中的平均值

How to calculate average in a multidimensional array conditionally if their first values are the same

ruby

ruby-on-rails

ruby-on-rails-4

数组是如何创建的