ruby:迭代期间无法将新 key 添加到哈希中

Question

我有三个哈希:

db_headers = {"1"=>"first_name", "2"=>"last_name"}
csv_headers = {"1"=>"First Name", "2"=>"Last Name"}
csv_records = {"0"=>{"id"=>"11", "first_name"=>"first_0", "Last Name"=>"last_0", "created_at"=>"2014-08-12 17:02:28 UTC", "updated_at"=>"2014-08-12 17:02:28 UTC"}, "1"=>{"id"=>"12", "first_name"=>"first_1", "Last Name"=>"last_1", "created_at"=>"2014-08-12 17:02:28 UTC", "updated_at"=>"2014-08-12 17:02:28 UTC"}}

db_headers 和 csv_headers 通过它们的键匹配。例如，它们的键值“2”分别包含“last_name”和“Last Name”。我的目标是在 db_headers 和 csv_headers 之间的值不同的地方，其中键是相同的，那么我需要用 db_headers 的值交换 csv_records 中的键。因此，例如，csv_records 键将从“Last Name”更改为“last_name”，因为键“2”处的 db_headers 和 csv_headers 值不同。

这是我想出的:

  csv_records.each do |record_key,record_value|
    csv_headers.each do |csv_key,csv_value|
      if record_value.has_key? csv_value
          db_headers.each do |db_key, db_value|
            if csv_key == db_key
              csv_records[db_value] = csv_records.delete csv_value
              break
            end
          end
          break
      end
    end
  end

不幸的是它失败了:

RuntimeError: can't add a new key into hash during iteration
    from (irb):12:in `[]='
    from (irb):12:in `block (3 levels) in irb_binding'
    from (irb):10:in `each'
    from (irb):10:in `block (2 levels) in irb_binding'
    from (irb):8:in `each'
    from (irb):8:in `block in irb_binding'
    from (irb):7:in `each'
    from (irb):7

这使错误消失了:

csv_records.keys.each do |record_key|
    csv_headers.keys.each do |csv_key|
      if csv_records[record_key].has_key? csv_headers[csv_key]
          db_headers.keys.each do |db_key|
            if csv_key == db_key
              csv_records[db_headers[db_key]] = csv_records.delete csv_headers[csv_key]
              # break is needed becasue csv_key wont exist in next iteration
              break
            end
          end
      end
    end
  end

但 csv_records 现在应该有一个值 last_name，但它继续使用“Last Name”。

Answer 1

迭代 hash.keys 而不是 hash。 #keys 将生成一个与散列分开的数组，因此您不会在修改散列时弄乱迭代。