JavaScript R- eturn Array Item(s) With Largest Score

We have an array of arrays that contains the marks scored by some students in different subjects. We need to write a function that returns the top scorer(s) for each subject, handling cases where multiple students have the same highest score.

Problem Setup

Given this input data:

const arr = [
    ['Math', 'John', 100],
    ['Math', 'Jake', 89],
    ['Math', 'Amy', 93],
    ['Science', 'Jake', 89],
    ['Science', 'John', 89],
    ['Science', 'Amy', 83],
    ['English', 'John', 82],
    ['English', 'Amy', 81],
    ['English', 'Jake', 72]
];

We want to return an array of objects with one object per subject containing the top scorer(s):

[
    { "Subject": "Math",
      "Top": [
          { Name: "John", Score: 100}
      ]
    },
    { "Subject": "Science",
      "Top": [
          { Name: "Jake", Score: 89},
          { Name: "John", Score: 89}
      ]
    },
    { "Subject": "English",
      "Top": [
          { Name: "John", Score: 82}
      ]
    }
]

Solution Using Array.reduce()

The solution uses reduce() to iterate through the data and build the result array:

const arr = [
    ['Math', 'John', 100],
    ['Math', 'Jake', 89],
    ['Math', 'Amy', 93],
    ['Science', 'Jake', 89],
    ['Science', 'John', 89],
    ['Science', 'Amy', 83],
    ['English', 'John', 82],
    ['English', 'Amy', 81],
    ['English', 'Jake', 72]
];

const groupScore = arr => {
    return arr.reduce((acc, val) => {
        const [subject, name, score] = val;
        const existingIndex = acc.findIndex(el => el['Subject'] === subject);
        
        if (existingIndex !== -1) {
            // Subject already exists
            if (score > acc[existingIndex]["Top"][0]["score"]) {
                // New high score - replace all
                acc[existingIndex]["Top"] = [{
                    "name": name, "score": score
                }];
            } else if (score === acc[existingIndex]["Top"][0]["score"]) {
                // Tie for high score - add to list
                acc[existingIndex]["Top"].push({
                    "name": name, "score": score
                });
            }
        } else {
            // New subject
            acc.push({
                "Subject": subject,
                "Top": [{"name": name, "score": score}]
            });
        }
        return acc;
    }, []);
};

console.log(JSON.stringify(groupScore(arr), undefined, 2));

[
  {
    "Subject": "Math",
    "Top": [
      {
        "name": "John",
        "score": 100
      }
    ]
  },
  {
    "Subject": "Science",
    "Top": [
      {
        "name": "Jake",
        "score": 89
      },
      {
        "name": "John",
        "score": 89
      }
    ]
  },
  {
    "Subject": "English",
    "Top": [
      {
        "name": "John",
        "score": 82
      }
    ]
  }
]

How It Works

The algorithm processes each student record and:

• Destructures each array element into subject, name, and score
• Checks if the subject already exists using findIndex()
• Compares scores - if higher, replaces the top scorers; if equal, adds to the list
• Creates new entries for subjects not yet processed

Key Points

• Handles ties by keeping multiple top scorers for the same subject
• Uses array destructuring for cleaner code
• Efficiently finds existing subjects with findIndex()
• Returns properly formatted JSON structure

Conclusion

This solution effectively groups student scores by subject and identifies top performers, handling tied scores appropriately. The reduce() method provides a clean way to transform the nested array data into the desired object structure.