将对象数组转换为嵌套数组

const arr = [
  { id: 1, name: 'A', group: 'Group1' },
  { id: 2, name: 'B', group: 'Group2' },
  { id: 3, name: 'C', group: 'Group1' },
  { id: 4, name: 'D', group: 'Group2' }
];

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

console.log(nestedArr);

{
  Group1: [
    { id: 1, name: 'A', group: 'Group1' },
    { id: 3, name: 'C', group: 'Group1' }
  ],
  Group2: [
    { id: 2, name: 'B', group: 'Group2' },
    { id: 4, name: 'D', group: 'Group2' }
  ]
}

const nestedArr = Object.values(nestedObj).map(group => group);

console.log(nestedArr);

[
  [
    { id: 1, name: 'A', group: 'Group1' },
    { id: 3, name: 'C', group: 'Group1' }
  ],
  [
    { id: 2, name: 'B', group: 'Group2' },
    { id: 4, name: 'D', group: 'Group2' }
  ]
]