基于ruby中的某些键，对哈希数组的出现进行分组和显示

Question

我有一系列像这样的哈希：

[
  {"a"=>"first", "b"=>[{"lt"=>7, "lg"=>8}]},
  {"a"=>"first", "b"=>[{"lt"=>7, "lg"=>8}]},
  {"a"=>"second", "b"=>[{"lt"=>7, "lg"=>8}]},
  {"a"=>"third", "b"=>[{"lt"=>9, "lg"=>10}]}
]

如何按"a"键值显示事件并显示类似

的内容

[
  {{"a"=>"first", "b"=>[{"lt"=>7, "lg"=>8}]}=>2},
  {{"a"=>"second", "b"=>[{"lt"=>7, "lg"=>8}]}=>1},
  {{"a"=>"third", "b"=>[{"lt"=>9, "lg"=>10}]}=>1}
]

我正在寻找“红宝石方式”解决方案。

Answer 1

frequency_distribution

您可以使用带有哈希的each_with_object和默认出现值Enumerable#frequency_distribution来定义0：

module Enumerable
  def frequency_distribution
    each_with_object(Hash.new(0)) { |element, count| count[element] += 1 }
  end
end

它的工作原理如下：

require 'pp'
data = [
    {"a"=>"first", "b"=>[{"lt"=>7, "lg"=>8}]},
    {"a"=>"first", "b"=>[{"lt"=>7, "lg"=>8}]},
    {"a"=>"second", "b"=>[{"lt"=>7, "lg"=>8}]},
    {"a"=>"third", "b"=>[{"lt"=>9, "lg"=>10}]}
]

pp data.frequency_distribution
# {{"a"=>"first", "b"=>[{"lt"=>7, "lg"=>8}]}=>2,
#  {"a"=>"second", "b"=>[{"lt"=>7, "lg"=>8}]}=>1,
#  {"a"=>"third", "b"=>[{"lt"=>9, "lg"=>10}]}=>1}

如果你不想修补Enumerable：

def frequency_distribution(array)
  array.each_with_object(Hash.new(0)) { |e, h| h[e] += 1 }
end

frequency_distribution(data)
# {{"a"=>"first", "b"=>[{"lt"=>7, "lg"=>8}]}=>2,
#  {"a"=>"second", "b"=>[{"lt"=>7, "lg"=>8}]}=>1,
#  {"a"=>"third", "b"=>[{"lt"=>9, "lg"=>10}]}=>1}

请注意，输出是一个哈希。键是哈希值，值是整数。我想不出将它转换为1对哈希数组的任何好理由。查找速度会慢得多，而且可读性也会降低。

count_by

对于更通用的方法，您可以使用与Enumerable#count_by或group_by相同的语法定义sort_by：

module Enumerable
  def count_by(&block)
    each_with_object(Hash.new(0)) { |element, count| count[block.call(element)] += 1 }
  end
end

require 'pp'
data = [
    {"a"=>"first", "b"=>[{"lt"=>7, "lg"=>8}]},
    {"a"=>"first", "b"=>[{"lt"=>7, "lg"=>8}]},
    {"a"=>"second", "b"=>[{"lt"=>7, "lg"=>8}]},
    {"a"=>"third", "b"=>[{"lt"=>9, "lg"=>10}]}
]

pp data.count_by(&:itself)
# {{"a"=>"first", "b"=>[{"lt"=>7, "lg"=>8}]}=>2,
#  {"a"=>"second", "b"=>[{"lt"=>7, "lg"=>8}]}=>1,
#  {"a"=>"third", "b"=>[{"lt"=>9, "lg"=>10}]}=>1}

pp data.count_by(&:keys)
#=> {["a", "b"]=>4}

pp data.count_by{|key, value| key["a"]}
#=> {"first"=>2, "second"=>1, "third"=>1}

Answer 2

{{1}}

Answer 3

正如我理解的那样，它与给定数组的特定元素无关。更一般地说，给定一个数组

arr = [a,a,b,c] 

其中a，b和c是任何 Ruby对象，您需要计算每个唯一元素的数量，表示为哈希数组。为了简单起见，假设

arr = [1,1,2,3]

以下是通过arr进行单次传递来获取计数的两种方法。

arr.group_by(&:itself).map { |k,v| { k=>v.size } }
  #=> [{ 1=>2 }, { 2=>1 }, { 3=>1 }]

和（计算哈希，@ Eric在他的回答中使用）

arr.each_with_object(Hash.new(0)) { |e,h| h[e] += 1 }
  #=> [{ 1=>2 }, { 2=>1 }, { 3=>1 }]