groupBy.test.js

// FIXME: npm test /src/utils/groupBy.test.js

// 어떤 것을 해볼까요?
const groupBy = (arr, callback) => {
  return arr.reduce((acc, val) => {
    const key = callback(val);

    if (acc[key] === undefined) acc[key] = [];

    acc[key].push(val);
    return acc;
  }, {});
};

describe("groupBy 테스트", () => {
  describe("non-lazy", () => {
    it("case: 1, Normal", () => {
      const array = [6.1, 4.2, 6.3];
      const grouped = groupBy(array, Math.floor);

      expect(grouped).toEqual({ 4: [4.2], 6: [6.1, 6.3] });
    });

    it("case: 2, Advanced", () => {
      const array = [
        [1, "a"],
        [2, "a"],
        [2, "b"],
      ];

      // 두 번째 인자가 index
      const [groupedFirstIndex, groupedSecondIndex] = [
        groupBy(array, 0),
        groupBy(array, 1),
      ];

      expect(groupedFirstIndex).toEqual({
        1: [[1, "a"]],
        2: [
          [2, "a"],
          [2, "b"],
        ],
      });

      expect(groupedSecondIndex).toEqual({
        a: [
          [1, "a"],
          [2, "a"],
        ],
        b: [[2, "b"]],
      });
    });

    it("case: 3, Advanced", () => {
      const grouped = groupBy({ a: 6.1, b: 4.2, c: 6.3 }, Math.floor);

      expect(grouped).toEqual({ 4: [4.2], 6: [6.1, 6.3] });
    });
  });
});