使用对象键中的日期对结果进行分组，并且只获取计数结果

Question

你好，我很难使用MongoDB或Javascript获得这个复杂的返回。希望有人能教我如何得到这个回报。

管理

>.分组结果

用户平的结果

下面是数据示例。

let user = [
{
_id: 123,
name: 'John',
createdAt: "2015-08-12T00:00:00Z"
},
{
_id: 124,
name: 'Jane',
createdAt: "2015-09-12T00:00:00Z"
},
{
_id: 125,
name: 'Robert',
createdAt: "2015-09-12T00:00:00Z"
},
{
_id: 126,
name: 'Samson',
createdAt: "2016-11-12T00:00:00Z"
}
]

预期的结果用户

[
{
"15-8": 1 //yyyy-mm: number of data for the month of august
},
{
"15-9": 2
},
{
"16-11": 1
}
]

管理>

[
{
"15-8": 
{
_id: 123,
count: 1
}
},
{
"15-9": {
_id: 124,
count: 1,
},{
_id: 125,
count: 1
},
{
"16-11": {
_id: 126,
count: 1
}
}
]

Answer 1

1. 您应该具有从名为getKeyFromDate的日期字符串中获取key的功能，格式结果为YY-MM

2. 循环user数据来聚合您的数据，例如使用reduce。

let user = [
{
_id: 123,
name: 'John',
createdAt: "2015-08-12T00:00:00Z"
},
{
_id: 124,
name: 'Jane',
createdAt: "2015-09-12T00:00:00Z"
},
{
_id: 125,
name: 'Robert',
createdAt: "2015-09-12T00:00:00Z"
},
{
_id: 126,
name: 'Samson',
createdAt: "2016-11-12T00:00:00Z"
}
];
const getKeyFromDate = (dateString) => {
var date = new Date(dateString);
var year = date.getFullYear().toString().substr(2, 3);
var month = date.getMonth() + 1;
return `${year}-${month}`; // YY-MM
};
var result = user.reduce((acc, {createdAt}) => {
var key = getKeyFromDate(createdAt);
acc[key] = acc[key] || {[key]: 0}; //Also use shortcut like: acc[key] ??= {[key]: 0};
acc[key][key] += 1;
return acc; 

}, {});
console.log(Object.values(result));

如果你不熟悉.reduce，也可以使用for..of

var result2 = {};
for(let {createdAt} of user){
var key = getKeyFromDate(createdAt);
result2[key] = result2[key] || {[key]: 0};
result2[key][key] += 1;
}
console.log(Object.values(result2));