TypeScript中的array.groupBy

function groupBy<T, K>(arr: T[], keyGetter: (item: T) => K): { [key: string]: T[] } {
  const groupedObj: { [key: string]: T[] } = {};

  arr.forEach((item) => {
    const key = keyGetter(item);
    if (!groupedObj[key]) {
      groupedObj[key] = [];
    }
    groupedObj[key].push(item);
  });

  return groupedObj;
}

type Student = {
  name: string;
  class: string;
};

const students: Student[] = [
  { name: "Alice", class: "A" },
  { name: "Bob", class: "B" },
  { name: "Charlie", class: "A" },
  { name: "David", class: "C" },
];

const groupedStudents = groupBy(students, (student) => student.class);

{
  A: [
    { name: "Alice", class: "A" },
    { name: "Charlie", class: "A" },
  ],
  B: [
    { name: "Bob", class: "B" },
  ],
  C: [
    { name: "David", class: "C" },
  ]
}