如何在多维数组与一维对象中匹配ID，避免过多嵌套循环？

Hey there! I see you've got a working solution using nested map calls, but we can definitely make this more efficient—especially if your dataset grows larger. Let's break down the issues with the original approach and build a better version.

What's Less Efficient in the Original Code #

• You're looping through all keys in storedOBJ for every single question—that's a lot of redundant checks. If you have 100 pages, 10 questions per page, and 50 entries in storedOBJ, that's 50,000 extra iterations!
• Using nested map plus manual push to build the result array works, but it's a bit clunky and harder to read at a glance.

A Faster, Cleaner Approach #

Instead of checking every key in storedOBJ for each question, we can leverage object key lookups (which are O(1) time!) and use array methods that streamline the process:

const getMatchingIDs = function(pages, storedOBJ) {
  // Use flatMap to flatten nested results in one go
  return pages.flatMap(page => 
    page.questions
      // First, filter out questions that don't exist in storedOBJ (skip unnecessary work)
      .filter(question => storedOBJ.hasOwnProperty(question.questionText))
      // For matching questions, build the ID pair directly
      .map(question => {
        const answerIndex = storedOBJ[question.questionText];
        const answerID = question.answers[answerIndex].id;
        return `${question.id}:${answerID}`;
      })
  );
};

Why This Works Better #

1. O(1) Key Lookups: Instead of looping through all storedOBJ keys for each question, we just check if the question's text exists as a key, then grab the index instantly. This drops the time complexity from O(P*Q*S) to O(P*Q) (P = number of pages, Q = questions per page, S = entries in storedOBJ).
2. flatMap for Clean Flattening: No more manually pushing to an array—flatMap handles turning nested question results into a single flat array automatically.
3. Early Filtering: We filter out non-matching questions first, so we don't waste time processing questions that have no corresponding entry in storedOBJ.

Testing with Your Sample Data #

Let's plug in your example to confirm it works:

const pages = [
  {
    questions: [
      { id: 987, questionText: 'Some Question', answers: [{ id: 154 }, { id: 232 }, { id: 312 }] },
      { id: 324, questionText: 'Another Question', answers: [{ id: 154 }, { id: 232 }, { id: 312 }] },
      { id: 467, questionText: 'Last Question', answers: [{ id: 154 }, { id: 232 }, { id: 312 }] }
    ]
  }
];
const storedOBJ = { 'Some Question': 0, 'Last Question': 0, 'Another Question': 2 };

console.log(getMatchingIDs(pages, storedOBJ)); 
// Output: ["987:154", "324:312", "467:154"] — exactly what you need!

Bonus: Add Safety Checks #

If you want to handle edge cases (like invalid answer indexes), you can add a quick validation step:

.map(question => {
  const answerIndex = storedOBJ[question.questionText];
  // Make sure the index is a valid number within the answers array bounds
  if (typeof answerIndex === 'number' && answerIndex >= 0 && answerIndex < question.answers.length) {
    const answerID = question.answers[answerIndex].id;
    return `${question.id}:${answerID}`;
  }
  // Optional: Return null or skip invalid entries
  return null;
})
// Filter out any null results from invalid indexes
.filter(Boolean)

内容的提问来源于stack exchange，提问作者Jaeeun Lee