/**
 * 根据函数映射每个元素，然后求数组的平均值
 * @param arr
 * @param fn
 */
export const averageBy = (
    arr: {
        map: (
            arg0: any
        ) => {
            reduce: (arg0: (acc: any, val: any) => any, arg1: number) => number;
        };
        length: number;
    },
    fn: string | number
) =>
    arr
        .map(
            typeof fn === "function"
                ? fn
                : (val: { [x: string]: any }) => val[fn]
        )
        .reduce((acc, val) => acc + val, 0) / arr.length;