如何计算 Ruby 哈希中特定值的出现次数？

Question

我有一个 Ruby 哈希（最初是 rails 中的一个参数）

如何计算每个 answers_attributes 中 correctness 的数量？

（为什么我这样做是因为我试图通过 rails 创建一个多项选择测验。一个问题可能有很多答案。我试图使用 multi_correct 复选框来决定哪个问题有很多正确答案。但这有点违反直觉。所以我希望后端通过计算每个问题的正确数量来决定）

{
  "utf8" => "✓", "authenticity_token" => "r5xX46JG/GPF6+drEWmMPR+LpOI0jE0Tta/ABQ0rZJJE+UbbEjvNMLP6y2Z9IsWlXq27PR6Odx0EK4NECPjmzQ==", "question_bank" => {
    "name" => "123213", "questions_attributes" => {
      "0" => {
        "content" => "question 1", "multi_correct" => "no", "answers_attributes" => {
          "0" => {
            "content" => "as1", "correctness" => "false"
          }, "1" => {
            "content" => "as2", "correctness" => "false"
          }, "2" => {
            "content" => "as3", "correctness" => "true"
          }, "3" => {
            "content" => "as4", "correctness" => "false"
          }
        }
      }, "1" => {
        "content" => "q2", "multi_correct" => "no", "answers_attributes" => {
          "0" => {
            "content" => "a1", "correctness" => "false"
          }, "1" => {
            "content" => "a2", "correctness" => "false"
          }, "2" => {
            "content" => "a3", "correctness" => "true"
          }, "3" => {
            "content" => "a4", "correctness" => "false"
          }
        }
      }, "2" => {
        "content" => "q3", "multi_correct" => "no", "answers_attributes" => {
          "0" => {
            "content" => "aa1", "correctness" => "false"
          }, "1" => {
            "content" => "aa2", "correctness" => "false"
          }, "2" => {
            "content" => "aa3", "correctness" => "false"
          }, "3" => {
            "content" => "aa4", "correctness" => "true"
          }
        }
      }
    }
  }, "commit" => "Submit"
}

Answer 1

如果您只想计算散列中有多少正确答案，可以使用 inject 来实现。这是一个方法：

# iterate over the questions
hash['question_bank']['questions_attributes'].values.inject(0) do |count, q|
  # iterate over the answers
  count += q['answers_attributes'].values.inject(0) do |a_count, a|
    a_count += a['correctness'] == 'true' ? 1 : 0
  end
end

Answer 2

我将其解释为寻找每个问题的正确答案数。如果是这样，您可以使用以下方法实现此目的：

your_hash['question_bank']['questions_attributes'].values.reduce(Hash.new(0)) do |hash, question| 
  question['answers_attributes'].each do |_k, answer| 
    hash[question['content']] += 1 if answer['correctness'] == 'true'
  end
  hash
end

这给出了结果：

# => {"question 1"=>1, "q2"=>1, "q3"=>1}

基本上，代码的作用是：

遍历问题，使用 reduce 使默认值为 0 的散列可用
遍历此问题的答案，并在答案正确时将 1 添加到随附的 hash[question_name]（或示例中的 hash[question['content']]）
returns 随附的散列

如果您正在使用 Rails，对参数的引用可能暗示了这一点，请考虑使用 each_with_object 而不是 reduce；这样你就可以避免示例中的尾随 hash 因为它总是 returns 累加器。

希望对您有所帮助 - 如果您有任何问题，请告诉我。

如何计算 Ruby 哈希中特定值的出现次数？

How to count number of appearance of a specific value in Ruby hash?

ruby

ruby-hash