使用 TypeScript 实现类型安全的 Group By 和 Sum 操作

/**
 * Sums object value(s) in an array of objects, grouping by arbitrary object keys.
 *
 * @remarks
 * This method takes and returns an array of objects.
 * The resulting array of object contains a subset of the object keys in the
 * original array.
 *
 * @param arr - The array of objects to group by and sum.
 * @param groupByKeys - An array with the keys to group by.
 * @param sumKeys - An array with the keys to sum. The keys must refer
 *    to numeric values.
 * @returns An array of objects, grouped by groupByKeys and with the values
 *    of keys in sumKeys summed up.
 */
const groupBySum = <T, K extends keyof T, S extends keyof T>(
  arr: T[],
  groupByKeys: K[],
  sumKeys: S[]
): Pick<T, K | S>[] => {
  return [
    ...arr
      .reduce((accu, curr) => {
        const keyArr = groupByKeys.map((key) => curr[key]);
        const key = keyArr.join("-");
        const groupedSum =
          accu.get(key) ||
          Object.assign(
            {},
            Object.fromEntries(groupByKeys.map((key) => [key, curr[key]])),
            Object.fromEntries(sumKeys.map((key) => [key, 0]))
          );
        for (let key of sumKeys) {
          groupedSum[key] += curr[key];
        }
        return accu.set(key, groupedSum);
      }, new Map())
      .values(),
  ];
};

const arr = [
  { shape: "square", color: "red", available: 1, ordered: 1 },
  { shape: "square", color: "red", available: 2, ordered: 1 },
  { shape: "circle", color: "blue", available: 0, ordered: 3 },
  { shape: "square", color: "blue", available: 4, ordered: 4 },
];

// Group by "shape" and sum "available"
const result1 = groupBySum(arr, ["shape"], ["available"]);
console.log('groupBySum(arr, ["shape"], ["available"])')
console.log(result1);
// Output:
// [
//   { shape: "square", available: 7 },
//   { shape: "circle", available: 0 }
// ]

// Group by "color" and sum "ordered"
const result2 = groupBySum(arr, ["color"], ["ordered"]);
console.log('\n\ngroupBySum(arr, ["color"], ["ordered"])')
console.log(result2);
// Output:
// [
//   { color: "red", ordered: 2 },
//   { color: "blue", ordered: 7 }
// ]

// Group by "shape" and "color" and sum "available" and "ordered"
const result3 = groupBySum(arr, ["shape", "color"], ["available", "ordered"]);
console.log('\n\ngroupBySum(arr, ["shape", "color"], ["available", "ordered"])')
console.log(result3);
// Output:
// [
//   { shape: "square", color: "red", available: 3, ordered: 2 },
//   { shape: "circle", color: "blue", available: 0, ordered: 3 },
//   { shape: "square", color: "blue", available: 4, ordered: 4 }
// ]

// @ts-expect-error
groupBySum(arr, ["blah"], ["ordered"]); // Error: Type '"blah"' is not assignable to type '"shape" | "ordered" | "color" | "available"'.ts(2322)

const ans = groupBySum(arr, ["shape"], ["ordered"]);