使用哈希表或哈希映射将数组中的对象值更新为另一个数组中的值

Question

我有两个数组 Array1 和 Array2，我正在更新 Array1 中对象的速率，并在数组 2 中使用相同对象（具有相同 ID）的速率。我有一个函数可以遍历两个数组以获取期望的结果。在浏览了一些关于堆栈溢出的答案后，我觉得哈希表最适合降低复杂性。我只是想了解如何使用 has 映射来实现相同的功能。

let Array1 = [{
    id: 1,
    name: "IceCream",
    details: [{
        id: "12",
        name: "milk",
        quantity: "50",
        rate: "100"
      },
      {
        id: "13",
        name: "cream",
        quantity: "50",
        rate: "300"
      }
    ]
  },
  {
    id: 2,
    name: "Coffee",
    details: [{
        id: "14",
        name: "Coffee bean",
        quantity: "60",
        rate: "200"
      },
      {
        id: "15",
        name: "water",
        quantity: "60",
        rate: "300"
      }
    ]
  },
  {
    id: 3,
    name: "Tea",
    details: [{
      id: "16",
      name: "Tea leaf",
      quantity: "50",
      rate: "700"
    }]
  }
]
let Array2 = [{
    id: 1,
    name: "IceCream",
    details: [{
        id: "12",
        name: "milk",
        quantity: "50",
        rate: "500"
      },
      {
        id: "13",
        name: "cream",
        quantity: "50",
        rate: "700"
      }
    ]
  },
  {
    id: 2,
    name: "Coffee",
    details: [{
        id: "14",
        name: "Coffee bean",
        quantity: "60",
        rate: "800"
      },
      {
        id: "15",
        name: "water",
        quantity: "60",
        rate: "8000"
      }
    ]
  }
]
Array1 = Array1.map(item => {
  let element = Array2.find(e => e.id == item.id);
  if (element) {
    item.details = item.details.map(e => {
      let detail = element.details.find(d => d.id == e.id);
      if (detail)
        e.rate = detail.rate;
      return e;
    });
  }
  return item;
});
console.log(Array1);

Answer 1

制作Array2 的项目（按id）和Array2 的每个细节（按id）的映射，然后您可以迭代Array1 并以低复杂度改变其属性：

const items2ById = {};
for (const item of Array2) {
  items2ById[item.id] = item;
}
const items2DetailsById = {};
for (const detail of Array2.flatMap(({ details }) => details)) {
  items2DetailsById[detail.id] = detail;
}
for (const item of Array1) {
  if (!items2ById[item.id]) continue;
  for (const detail of item.details) {
    if (items2DetailsById[detail.id]) {
      detail.rate = items2DetailsById[detail.id].rate;
    }
  }
}

请注意，由于您正在对现有对象进行变异，.map 并不合适，因为您并不真正关心创建新数组 - 相反，只需遍历数组并根据需要对其进行变异。

let Array1 = [{
    id: 1,
    name: "IceCream",
    details: [{
        id: "12",
        name: "milk",
        quantity: "50",
        rate: "100"
      },
      {
        id: "13",
        name: "cream",
        quantity: "50",
        rate: "300"
      }
    ]
  },
  {
    id: 2,
    name: "Coffee",
    details: [{
        id: "14",
        name: "Coffee bean",
        quantity: "60",
        rate: "200"
      },
      {
        id: "15",
        name: "water",
        quantity: "60",
        rate: "300"
      }
    ]
  },
  {
    id: 3,
    name: "Tea",
    details: [{
      id: "16",
      name: "Tea leaf",
      quantity: "50",
      rate: "700"
    }]
  }
]
let Array2 = [{
    id: 1,
    name: "IceCream",
    details: [{
        id: "12",
        name: "milk",
        quantity: "50",
        rate: "500"
      },
      {
        id: "13",
        name: "cream",
        quantity: "50",
        rate: "700"
      }
    ]
  },
  {
    id: 2,
    name: "Coffee",
    details: [{
        id: "14",
        name: "Coffee bean",
        quantity: "60",
        rate: "800"
      },
      {
        id: "15",
        name: "water",
        quantity: "60",
        rate: "8000"
      }
    ]
  }
];
const items2ById = {};
for (const item of Array2) {
  items2ById[item.id] = item;
}
const items2DetailsById = {};
for (const detail of Array2.flatMap(({ details }) => details)) {
  items2DetailsById[detail.id] = detail;
}
for (const item of Array1) {
  if (!items2ById[item.id]) continue;
  for (const detail of item.details) {
    if (items2DetailsById[detail.id]) {
      detail.rate = items2DetailsById[detail.id].rate;
    }
  }
}
console.log(Array1);