数组对象内相同值的重复分组

[{
    "_id": {
        "year": 2017,
        "month": 4
    },
    "Confirm": 0
}, {
    "_id": {
        "year": 2017,
        "month": 4
    },
    "Expired": 25
}, {
    "_id": {
        "year": 2017,
        "month": 4
    },
    "Pending": 390
}, {
    "_id": {
        "year": 2017,
        "month": 5
    },
    "Pending": 1400
}]

上面的数组包含相同的月份和年份值。从 MongoDB 聚合生成。我想将它们合并到一个对象中并保留它们拥有的任何键和值。

预期输出：

[{
    month: 4,
    year: 2017,
    Expired: 25,
    Pending: 390
}, {
    month: 5,
    year: 2017,
    Pending: 1400
}]

我更喜欢最快的执行实现。欢迎使用 Underscorejs 或本地语言。谢谢

这需要一点点区分，但它是线性的：

const ary = [{
    "_id": {
        "year": 2017,
        "month": 4
    },
    "Confirm": 0
}, {
    "_id": {
        "year": 2017,
        "month": 4
    },
    "Expired": 25
}, {
    "_id": {
        "year": 2017,
        "month": 4
    },
    "Pending": 390
}, {
    "_id": {
        "year": 2017,
        "month": 5
    },
    "Pending": 1400
}];

const result = Object.values(ary.reduce((acc, cur) => {
    const { month, year } = cur._id;
    const key = `${month}-${year}`;
    const obj = Object.assign({}, cur);
    delete obj._id;
    acc[key] = Object.assign(acc[key] || { month, year }, obj);
    return acc;
}, {}));

console.log(result);