JavaScript Group By ID with Average Score: Two Approaches Quiz

Implement groupedAverageScore(arr, key) so it groups items by the property named key, then returns an object mapping each group key to { total, average } where total is the group size and average is the mean of score. Round each average to four decimal places.

Examples

Example 1:

Input: groupedAverageScore([{id:1,score:10},{id:1,score:20},{id:2,score:30}], 'id')
Output: { '1': { total: 2, average: 15 }, '2': { total: 1, average: 30 } }
Explanation: group 1 has two scores 10 and 20 (average 15) and group 2 has one score 30 (average 30).