数据分组

interface GroupResult<T> {
	[key: string]: Array<T>;
}
const groupBy = <T>(
	arr: Array<T>,
	generateKey: (item: T, i: number, arr: Array<T>) => string
) => {
	const result: GroupResult<T> = {};

	if (typeof generateKey === 'string') {
		const paramName = generateKey;
		generateKey = (p) => p[paramName];
	}

	for (let i = 0; i < arr.length; ++i) {
		const key = generateKey(arr[i], i, arr);
		if (result[key]) {
			result[key].push(arr[i]);
		} else {
			result[key] = [arr[i]];
		}
	}

	return result;
};