转换对象数组(按groupby排序)

const arr = [
  { name: 'Alice', group: 'A', age: 25 },
  { name: 'Bob', group: 'B', age: 30 },
  { name: 'Charlie', group: 'A', age: 35 },
  { name: 'David', group: 'C', age: 40 },
  { name: 'Eve', group: 'B', age: 20 }
];

const result = arr.reduce((groups, obj) => {
  const group = obj.group;
  if (!groups[group]) {
    groups[group] = [];
  }
  groups[group].push(obj);
  return groups;
}, {});

for (const group in result) {
  result[group].sort((a, b) => a.age - b.age);
}

console.log(result);

{
  A: [
    { name: 'Alice', group: 'A', age: 25 },
    { name: 'Charlie', group: 'A', age: 35 }
  ],
  B: [
    { name: 'Eve', group: 'B', age: 20 },
    { name: 'Bob', group: 'B', age: 30 }
  ],
  C: [
    { name: 'David', group: 'C', age: 40 }
  ]
}