比较两个 json 对象并附加唯一项

Question

我有两个 JSON 文件 - 一个从服务器获取 (data)，另一个是本地 (database)。

我正在尝试遍历服务器 json，将其与本地 json 进行比较，然后将任何新对象附加到本地文件中。这样，当脚本第二次运行时，这些新项目已被附加并且可以跳过。

问题：

目前当它在初始时间之后运行时，因为它检查a-a, a-b, a-c, b-a, b-b, b-c...，它将跳过初始结果，但随后添加其他选项。

我正在使用的 js：

let additions = [];
data.forEach(item1 => {
  database.filter(item2 => {
    if( !(item1.value === item2.value && item1.country === item2.country) ) {
      additions.push(item1)
    }
  })
});

示例/期望：

data = [
  { value: "qwert", country: "US" },
  { value: "asdfg", country: "CA" },
  { value: "zxcvb", country: "GB" }
] 

database = [
  { value: "poiuy", country: "CA" },
  { value: "qwert", country: "US" }
]

然后在循环和检查之后，它会导致以下（初始运行）：

output = [
  { value: "poiuy", country: "CA" },
  { value: "qwert", country: "US" },
  { value: "asdfg", country: "CA" },
  { value: "zxcvb", country: "GB" }
] 

当我下次运行循环时，如果数据发生了变化：

data = [
  { value: "poiuy", country: "CA" },
  { value: "wsxcd", country: "AU" },
  { value: "rfvbg", country: "NZ" },
  { value: "zxcvb", country: "FR" }
]

我期待这个：

output = [
  { value: "poiuy", country: "CA" },
  { value: "qwert", country: "US" },
  { value: "asdfg", country: "CA" },
  { value: "zxcvb", country: "GB" },
  { value: "wsxcd", country: "AU" },
  { value: "rfvbg", country: "NZ" },
  { value: "zxcvb", country: "FR" }
]

但我收到了这个：

output = [
  { value: "poiuy", country: "CA" },
  { value: "qwert", country: "US" },
  { value: "asdfg", country: "CA" },
  { value: "zxcvb", country: "GB" },
  { value: "poiuy", country: "CA" },
  { value: "poiuy", country: "CA" },
  { value: "poiuy", country: "CA" },
  { value: "wsxcd", country: "AU" },
  { value: "wsxcd", country: "AU" },
  { value: "wsxcd", country: "AU" },
  { value: "rfvbg", country: "NZ" },
  { value: "rfvbg", country: "NZ" },
  { value: "rfvbg", country: "NZ" },
  { value: "zxcvb", country: "FR" },
  { value: "zxcvb", country: "FR" },
  { value: "zxcvb", country: "FR" }
]

任何帮助都将不胜感激，因为我似乎无法弄清楚它只会附加唯一的项目，而不是逐个项目。

Answer 1

您可以使用array#reduce 在对象累加器中基于value 和country 获取唯一值。然后使用 Object.values() 从这些对象中获取所有值。

const localData = [ { value: "qwert", country: "US" }, { value: "asdfg", country: "CA" }, { value: "zxcvb", country: "GB" }],
      database = [{ value: "poiuy", country: "CA" }, { value: "qwert", country: "US" }],
      getUnique = (arr1, arr2) => Object.values([...arr1, ...arr2].reduce((r,o) => {
        const key = `${o.value}_${o.country}`;
        r[key] ??= o;
        return r;
      },{}));
console.log(getUnique(localData, database));

Answer 2

如果我理解正确，最简单但不是最快的方法是简单地合并数组然后过滤唯一值。

let data = [
  { value: "qwert", country: "US" },
  { value: "asdfg", country: "CA" },
  { value: "zxcvb", country: "GB" }
] 

let database = [
  { value: "poiuy", country: "CA" },
  { value: "qwert", country: "US" }
]

const getUniqueUnion = (data1, data2) => {
  return [...data1, ...data2].reduce((acc, cur) => {
    const match = acc.find((el) => {
      return el.country === cur.country && el.value === cur.value;
    });
    
    if (!match) {
      acc.push(cur);
    }
    
    return acc;
  }, []);
}

const result = getUniqueUnion(data, database);
console.log(result);

/*
  [
  {
    "value": "qwert",
    "country": "US"
  },
  {
    "value": "asdfg",
    "country": "CA"
  },
  {
    "value": "zxcvb",
    "country": "GB"
  },
  {
    "value": "poiuy",
    "country": "CA"
  }
]
*/

data = [
  { value: "poiuy", country: "CA" },
  { value: "wsxcd", country: "AU" },
  { value: "rfvbg", country: "NZ" },
  { value: "zxcvb", country: "FR" }
];

const result2 = getUniqueUnion(data, database);

console.log(result2);

/*
  [
  {
    "value": "poiuy",
    "country": "CA"
  },
  {
    "value": "wsxcd",
    "country": "AU"
  },
  {
    "value": "rfvbg",
    "country": "NZ"
  },
  {
    "value": "zxcvb",
    "country": "FR"
  },
  {
    "value": "qwert",
    "country": "US"
  }
]
*/

Answer 3

您可以按国家/地区对 database 数组进行分组，从而生成从国家到值集的映射。使用哈希映射和集合将避免重复。

分组做：

let reducer = (acc, curr) => {
  let {country, value} = curr;

  if (acc.hasOwnProperty(country)) {
    acc[country].add(value);
  } else {
    acc[country] = new Set([value]);
  }

  return acc;
};
let groupedDatabase = database.reduce(reducer, {});

然后你遍历你的data 并将每个条目分配给groupedDatabase。我们可以使用相同的 reducer：

let intermediateResult = data.reduce(reducer, groupedDatabase);

每次data变化，更新intermediateResult：

intermediateResult = data.reduce(reducer, groupedDatabase);

最后，将分组数据转回数组：

let output = Object.keys(intermediateResult).reduce((acc, curr) => {
  let entries = Array.from(intermediateResult[curr]).map(value => {
    return {country: curr, value}
   });

  acc.push(...entries);
  return acc;
}, []);

这是假设您只想跳过看到的记录以避免重复，而不是出于性能原因。

旁注： reducer 改变传递的初始值，例如groupedDatabase。这使您能够使用完全相同的函数调用（data.reduce(reducer, groupedDatabase); 部分）更新intermediateResult。由于突变，请务必仅在此上下文中使用groupedDatabase。如果你最终想在其他地方使用它（虽然我认为你不会，因为我只是为了这个目的才引入它），首先使用let copiedGroupedDatabase = Object.assign({}, groupedDatabase) 复制它，否则当它的值从你下面发生变化时你可能会感到惊讶.