以无点样式对对象数组进行GroupBy和reduce

// 假设有一个对象数组
const data = [
  { name: 'Alice', age: 25, city: 'New York' },
  { name: 'Bob', age: 30, city: 'Los Angeles' },
  { name: 'Charlie', age: 25, city: 'New York' },
  { name: 'David', age: 30, city: 'Chicago' }
];

// 自定义 groupBy 函数
function groupBy(array, key) {
  return array.reduce((result, item) => {
    const groupKey = item[key];
    if (!result[groupKey]) {
      result[groupKey] = [];
    }
    result[groupKey].push(item);
    return result;
  }, {});
}

// 使用 groupBy 函数按城市分组
const groupedByCity = groupBy(data, 'city');
console.log(groupedByCity);

// 输出:
// {
//   'New York': [
//     { name: 'Alice', age: 25, city: 'New York' },
//     { name: 'Charlie', age: 25, city: 'New York' }
//   ],
//   'Los Angeles': [
//     { name: 'Bob', age: 30, city: 'Los Angeles' }
//   ],
//   'Chicago': [
//     { name: 'David', age: 30, city: 'Chicago' }
//   ]
// }

// 确保每个对象都有 'city' 键
const cleanedData = data.map(item => ({
  ...item,
  city: item.city || 'Unknown'
}));

const groupedByCity = groupBy(cleanedData, 'city');
console.log(groupedByCity);