js 计算对象数组中某个属性值重复出现的个数

let list = [

    　　{name:"历下区",code:6},

    　　{name:"历下区",code:6},

    　　{name:"历下区",code:6},

    　　{name:"历城区",code:7},

    　　{name:"历城区",code:7},

    　　{name:"市中区",code:8},

    　　{name:"槐荫区",code:2},

    ];

//怎么将list转换为下面格式：

//num，相同的元素重复次数

[

     {name:"历下区",num:3},

  　{name:"历城区",num:2},　

  　{name:"市中区",num:1},

  　{name:"槐荫区",num:1}

  ]

 

步骤：

1. 首先要先获取所有需要计算的属性值

//先根据所有的name组合成一个数组

let titleList = list.map(item => {

    return item.name

})

 

//获得["历下区", "历下区", "历下区", "历城区", "历城区", "市中区", "槐荫区"]

2.将上面返回的结果变成：{历下区: 1, 历城区: 1, 市中区: 3,槐荫区:1}

function getRepeatNum(){

    return titleList.reduce((prev,next)=>{

        prev[next] = (prev[next] + 1) || 1;

        return prev;

    },{});

}

console.log(getRepeatNum())；//{历下区: 1, 历城区: 1, 市中区: 3,槐荫区:1}

3.  得到最终结果

let myObj = this.getRepeatNum(titleList),winningList = [];

 

for(let i in myObj){

    let obj = {

        title:i,

        num:myObj[i]

    }

    winningList.push(obj)

}

console.log(winningList)

//[{"title":"历下区","num":3},{"title":"历城区","num":2},{"title":"市中区","num":1},{"title":"槐荫区","num":1}]