返回对象数组(来自对象数组)

Question

我有以下数据，我想返回一个不同的years数组(对象)。

我尝试了下面的函数，但我在数组中得到了一个数组。

​

const data = [{
    id: 1,
    name: "test1",
    years: [{
      id: 1,
      name: "year1"
    }, {
      id: 2,
      name: "year2"
    }]
  },
  {
    id: 2,
    name: "test2",
    years: [{
      id: 1,
      name: "year1"
    }]
  },
]

let years = data.map((s) => {
  return s.years
})
let distinctYears = Array.from(new Set(years.map(c => c.id))).map(id => {
  return {
    id: id,
    name: years.find(c => c.id === id).name,
  }
})

console.log(distinctYears);

​

期望的结果：

[
  {id: 1, name: "year1"},
  {id: 2, name: "year2"}
]

Answer 1

因为s.years()是一个数组，而data.map()返回一个结果数组，所以years必须是一个数组数组。

使用.reduce()来连接它们，而不是使用.map()。

​

const data = [{
    id: 1,
    name: "test1",
    years: [{
      id: 1,
      name: "year1"
    }, {
      id: 2,
      name: "year2"
    }]
  },
  {
    id: 2,
    name: "test2",
    years: [{
      id: 1,
      name: "year1"
    }]
  },
];

const years = data.reduce((a, {
  years
}) => a.concat(years), []);
let distinctYears = Array.from(new Set(years.map(c => c.id))).map(id => {
  return {
    id: id,
    name: years.find(c => c.id === id).name,
  }
});
console.log(distinctYears);

​

Answer 2

你有很多方法可以做到这一点。这里有一个，它不是一行代码，但它被分解成几个部分，以帮助我们了解发生了什么。

您的数据集：

let data =
[
  {
    id: 1,
    name: "test1",
    years: [{id: 1, name: "year1"}, {id: 2, name: "year2"} ]
  },
  {
    id: 2,
    name: "test2",
    years: [{id: 1, name: "year1"} ]
  },
]

使用.flatMap()创建包含所有项的一级数组：

let allItems = data.flatMap((item) => {
    return item.years.map((year) => {
        return year
    })
})

获取不同的项目：

let distinct = []

allItems.forEach((item) => {
    let matchingItem = distinct.find((match) => match.id == item.id && match.name == item.name)

    if(!matchingItem){
        distinct.push(item)
    }
})

在实践中：

let data = [{
    id: 1,
    name: "test1",
    years: [{
      id: 1,
      name: "year1"
    }, {
      id: 2,
      name: "year2"
    }]
  },
  {
    id: 2,
    name: "test2",
    years: [{
      id: 1,
      name: "year1"
    }]
  },
]

let allItems = data.flatMap((item) => {
  return item.years.map((year) => {
    return year
  })
})

let distinct = []

allItems.forEach((item) => {
  let matchingItem = distinct.find((match) => match.id == item.id && match.name == item.name)

  if (!matchingItem) {
    distinct.push(item)
  }
})

console.log(distinct)

​