javascript - 如何按id数组分组

Question

这个问题已经有答案了:

Most efficient method to groupby on an array of objects (61 个回答)

已关闭 3 年前。

大家好，可以帮我减少数组吗？我有两个数组，我需要在中间将其中一组分组。在这里您可以找到示例

我有对象数组

const arr = [{
    mid: 888,
    name: "test"
  },
  {
    mid: 888,
    name: "test1"
  },
  {
    mid: 888,
    name: "test2"
  },
  {
    mid: 777,
    name: "test10"
  },
]

但是我需要按中进行分组并得到类似的东西

const arr = [{
    mid: 888,
    projects: [{
        name: "test"
      },
      {
        name: "test1"
      },
      {
        name: "test2"
      },
    ]
  },
  {
    mid: 777,
    projects: [{
      name: "test10"
    }, ]
  }
]

Answer 1

const arr = [{
    mid: 888,
    name: "test"
  },
  {
    mid: 888,
    name: "test1"
  },
  {
    mid: 888,
    name: "test2"
  },
  {
    mid: 777,
    name: "test10"
  }
];

let newArray = []
arr.map(item => item.mid).filter((value, index, self)=> { 
    return self.indexOf(value) === index;
}).forEach((mid)=>{
    newArray.push({
        mid,
        projects: arr.filter(item => item.mid == mid).map(item =>{ return {name: item.name}; })
    })
})

console.log(newArray)

使用reduce的其他方式:

const arr = [{
    mid: 888,
    name: "test"
  },
  {
    mid: 888,
    name: "test1"
  },
  {
    mid: 888,
    name: "test2"
  },
  {
    mid: 777,
    name: "test10"
  }
];

newArray = arr.map(item => item.mid).filter((value, index, self)=> { 
    return self.indexOf(value) === index;
}).map(item=> { return {mid: item, projects: []}})

newArray = arr.reduce((res, current)=>{
    let index = newArray.map(item => item.mid).indexOf(current.mid);
    res[index].projects.push({name: current.name})
    
    return res;
}, newArray)

console.log(newArray)