Ruby中的MapReduce数组

我有两个这样的阵列：

["1","7","8","10"]

arrays = [["1","7","8","10"], ["1","2","3","6","9","11"]].reduce(:+)
arrays.inject(Hash.new(0)) { |memo, e| memo.update(e => memo[e] + 1) }
# "{ "1" => 2, "7" => 1, "8" => 1, "10" => 1, "2" => 1, "3" => 1, "6" => 1, "9" => 1, "11" => 1 }"

及

这些数组表示用户选择的名为

Place

的类中的ID。我想选择投票最多的位置ID。我尝试了

转置

，但由于数组大小不同，因此无法转置

本例的预期输出为：

{ "1" => 2, "7" => 1, "8" => 1, "10" => 1, "2" => 1, "3" => 1, "6" => 1, "9" => 1, "11" => 1 }

---

您可以将所有数组合并，并计算相同元素的数量，如下所示：

["1","7","8","10"]

arrays = [["1","7","8","10"], ["1","2","3","6","9","11"]].reduce(:+)
arrays.inject(Hash.new(0)) { |memo, e| memo.update(e => memo[e] + 1) }
# "{ "1" => 2, "7" => 1, "8" => 1, "10" => 1, "2" => 1, "3" => 1, "6" => 1, "9" => 1, "11" => 1 }"

获得此中间结果后，使用

max\u by

从散列中选择具有最大值的键：

arrays = [["1","7","8","10"], ["1","2","3","6","9","11"]].reduce(:+)
arrays.inject(Hash.new(0)) { |memo, e| memo.update(e => memo[e] + 1) }
      .max_by { |_, count| count }[0]
#=> "1"

这是另一种方式：

arr = [["1","7","8","10"], ["1","2","3","6","9","11"], ["1","2","7"]]

h = arr.flatten.sort_by(&:to_i).group_by(&:itself)
h.update(h) { |_,v| v.size }
  #=> {"1"=>3, "2"=>2, "3"=>1, "6"=>1, "7"=>2, "8"=>1, "9"=>1, "10"=>1, "11"=>1}

步骤如下：

a = arr.flatten
  #=> ["1", "7", "8", "10", "1", "2", "3", "6", "9", "11", "1", "2", "7"] 
b = a.sort_by(&:to_i)
  #=> ["1", "1", "1", "2", "2", "3", "6", "7", "7", "8", "9", "10", "11"] 
h = b.group_by(&:itself)
  #=> {"1"=>["1", "1", "1"], "2"=>["2", "2"], "3"=>["3"], "6"=>["6"],
  #    "7"=>["7", "7"], "8"=>["8"], "9"=>["9"], "10"=>["10"], "11"=>["11"]} 

如果您使用的是Ruby 2.2之前的版本（引入时），则需要编写：

h = b.group_by { |s| s }

最后：

h.update(h) { |_,v| v.size }
  #=> {"1"=>["1", "1", "1"], "2"=>["2", "2"], "3"=>["3"], "6"=>["6"],
  #    "7"=>["7", "7"], "8"=>["8"], "9"=>["9"], "10"=>["10"], "11"=>["11"]} 

这使用了（aka

merge！

）的形式，它使用一个块（这里是

{| u，v | v.size}

）来确定合并的两个哈希中存在的键的值（在本例中是所有键）

更新：该方法首次出现在Ruby v2.4中。这允许我们写以下内容

arr.flatten.
    sort_by(&:to_i).
    group_by(&:itself).
    transform_values(&:size)

---

但是我可以（并且将会）有更多的阵列，而且我需要第二个被选中的选项。我需要像

{1=>2，7=>1，8=>1}

这样的东西，以

array=[…]+[…]

开头很难，因为数组的数量可能会有所不同。我建议您将

array

视为数组的数组，然后添加

array.reduce（：+）

额外步骤。除此之外，回答得很好。@CarySwoveland:是的，你是对的。当他有两个以上的数组时，

flatten

或

reduce

更好。