如何比较具有高阶函数的数组？ JavaScript答案

【问题标题】：How to compare arrays with higher order functions? JavaScript如何比较具有高阶函数的数组？ JavaScript
【发布时间】：2020-12-04 02:46:17
【问题描述】：

我正在尝试将数组与分配的属性进行比较，我只能使用高阶函数（.map()、.filter()、.forEach()、.some() 等...） .数组是“userWishlist”，属性来自“parks”数组“parks[index].id”的对象中的 ID。有人对解决此类问题有什么建议吗？我的代码现在只返回：

[{"id":1,"name":"Acadia","areaInSquareKm":198.6,"location":{"state":"Maine"}}]

调用时：

getWishlistParksForUser(parks, users, "dwayne.m55")

为什么我的代码不会返回与“愿望清单”数组匹配的所有“公园”对象？

/* Function should compare the user's wishlist with the parks */
function getWishlistParksForUser(parks, users, userID) {
  let wishArray = [];
  // Find the user
  const findUser = Object.keys(users).filter(user => user == userID);
  // Create array out of wishlist
  const userWishlist = users[findUser].wishlist.map(list => list);
  // Compare the two arrays and push park into wishlist array
  const parkID = userWishlist.forEach((wish, index) => {
    if (wish === parks[index].id) wishArray.push(parks[index])
  })

  return wishArray;
}

// The users objects (non-editable)
const users = {
  "karah.branch3": {
    visited: [2],
    wishlist: [1, 3],
  },
  "dwayne.m55": {
    visited: [2, 3],
    wishlist: [1, 3],
  },
};

// The parks array (non-editable)
const parks = [{
    id: 1,
    name: "Acadia",
    areaInSquareKm: 198.6,
    location: {
      state: "Maine"
    },
  },
  {
    id: 2,
    name: "Canyonlands",
    areaInSquareKm: 1366.2,
    location: {
      state: "Utah"
    },
  },
  {
    id: 3,
    name: "Zion",
    areaInSquareKm: 595.9,
    location: {
      state: "Utah"
    },
  },
];

console.log(getWishlistParksForUser(parks, users, "dwayne.m55"));

【问题讨论】：

“从愿望清单中创建数组”。已经是数组了，为什么还要用map()做成数组呢？
findUser 只是一个包含userID 的数组。那有什么意义呢？为什么使用数组作为对象属性？只需使用users[userID].wishlist。

标签： javascript arrays object properties higher-order-functions

【解决方案1】：

问题在于index 是当前愿望清单元素的索引，但您将它用作parks 的索引。所以你只返回一个公园，如果它在parks数组中的索引与它在wishlist中的ID相同。

您需要使用find() 查找具有当前愿望清单 ID 的公园。

/* Function should compare the user's wishlist with the parks */
function getWishlistParksForUser(parks, users, userID) {
  let wishArray = [];
  const userWishlist = users[userID].wishlist;
  // Compare the two arrays and push park into wishlist array
  userWishlist.forEach((wish) => {
    let foundPark = parks.find(p => p.id == wish);
    if (foundPark) {
      wishArray.push(foundPark)
    }
  })

  return wishArray;
}

// The users objects (non-editable)
const users = {
  "karah.branch3": {
    visited: [2],
    wishlist: [1, 3],
  },
  "dwayne.m55": {
    visited: [2, 3],
    wishlist: [1, 3],
  },
};

// The parks array (non-editable)
const parks = [{
    id: 1,
    name: "Acadia",
    areaInSquareKm: 198.6,
    location: {
      state: "Maine"
    },
  },
  {
    id: 2,
    name: "Canyonlands",
    areaInSquareKm: 1366.2,
    location: {
      state: "Utah"
    },
  },
  {
    id: 3,
    name: "Zion",
    areaInSquareKm: 595.9,
    location: {
      state: "Utah"
    },
  },
];

console.log(getWishlistParksForUser(parks, users, "dwayne.m55"));

【讨论】：

【解决方案2】：

这里你可以直接使用来自用户 whishList 的地图来解决它

对于您将映射到公园上搜索的对象的每个愿望

/* Function should compare the user's wishlist with the parks */
function getWishlistParksForUser(parks, users, userID) {
  return users[userID].wishlist.map(wishId => parks.find(p => p.id == wishId));
}

// The users objects (non-editable)
const users = {
  "karah.branch3": {
    visited: [2],
    wishlist: [1, 3],
  },
  "dwayne.m55": {
    visited: [2, 3],
    wishlist: [1, 2],
  },
};

// The parks array (non-editable)
const parks = [{
    id: 1,
    name: "Acadia",
    areaInSquareKm: 198.6,
    location: {
      state: "Maine"
    },
  },
  {
    id: 2,
    name: "Canyonlands",
    areaInSquareKm: 1366.2,
    location: {
      state: "Utah"
    },
  },
  {
    id: 3,
    name: "Zion",
    areaInSquareKm: 595.9,
    location: {
      state: "Utah"
    },
  },
];

console.log(getWishlistParksForUser(parks, users, "dwayne.m55"));

【讨论】：

【解决方案3】：

你的代码有两个问题，

const findUser = Object.keys(users).filter(user => user == userID); 不需要这样做，因为您可以使用 user[userId] 来获取特定用户，因为 user 是一个像地图这样的对象。
const selectedItem = parks.find(item => item.id === wish)您需要另一种搜索方法来为您找到正确的parkitem，仅获取与userWishlist相同索引的部分项目将无法解决问题。

我修改了你的代码，请试试这个

/* Function should compare the user's wishlist with the parks 

*/
function getWishlistParksForUser(parks, users, userID) {
  let wishArray = [];
  // Find the user
//   const findUser = Object.keys(users).filter(user => user == userID);
  // Create array out of wishlist
  const userWishlist = users[userID].wishlist.map(list => list);
  // Compare the two arrays and push park into wishlist array
  const parkID = userWishlist.forEach((wish, index) => {
    const selectedItem = parks.find(item => item.id === wish)
    if (selectedItem) wishArray.push(selectedItem)
  })

  return wishArray;
}

// The users objects (non-editable)
const users = {
  "karah.branch3": {
    visited: [2],
    wishlist: [1, 3],
  },
  "dwayne.m55": {
    visited: [2, 3],
    wishlist: [1, 3],
  },
};

// The parks array (non-editable)
const parks = [{
    id: 1,
    name: "Acadia",
    areaInSquareKm: 198.6,
    location: {
      state: "Maine"
    },
  },
  {
    id: 2,
    name: "Canyonlands",
    areaInSquareKm: 1366.2,
    location: {
      state: "Utah"
    },
  },
  {
    id: 3,
    name: "Zion",
    areaInSquareKm: 595.9,
    location: {
      state: "Utah"
    },
  },
];

console.log(getWishlistParksForUser(parks, users, "dwayne.m55"));

【讨论】：