javascript 减少数组中对象的多个键

Question

我有以下类型的对象映射（下面的示例数据）

{[date:string]:Array<{[type:string]:{amount:number, price:number}}>}

并且我需要将数组缩减为单个对象的金额总和和平均价格

我已经阅读了一些关于如何减少像

这样的对象的数据的post

Javascript reduce on array of objects

在我的例子中，"type" 是 ["PV"、"BHKW"、"FALLBACK"] 的 ENUM，但它可以扩展。除了在循环中编写声明外，我不知道如何使用 array.reduce 来更优雅地完成此操作。

有什么建议吗？

{
    "2018-08-01T11:00:00+02:00": [
        {
            "BHKW": {
                "amount": 131,
                "price": 85
            },
            "FALLBACK": {
                "amount": 84,
                "price": 1
            }
        },
        {
            "BHKW": {
                "amount": 307,
                "price": 58
            },
            "PV": {
                "amount": 4,
                "price": 60
            }
        }
    ],
    "2018-08-01T12:00:00+02:00": [
        {
            "BHKW": {
                "amount": 288,
                "price": 59
            },
            "PV": {
                "amount": 742,
                "price": 73
            }
        },
        {
            "BHKW": {
                "amount": 250,
                "price": 49
            },
            "PV": {
                "amount": 507,
                "price": 98
            }
        },
        {
            "PV": {
                "amount": 368,
                "price": 22
            },
            "BHKW": {
                "amount": 357,
                "price": 73
            }
        },
        {
            "FALLBACK": {
                "amount": 135,
                "price": 62
            },
            "BHKW": {
                "amount": 129,
                "price": 93
            }
        }
    ],

Answer 1

解决了！

var x = _.reduce(
    list,
    (acc, item) => {
        for (const key in item) {
            if (!acc[key]) {
                acc[key] = { price: 0, amount: 0 };
            }

            if (item[key] && item[key].price) {
                acc[key].price += item[key].price;
            }

            if (item[key] && item[key].amount) {
                acc[key].amount += item[key].amount;
            }
        }
        return acc;
    },
    {}
);

Answer 2

您可以将 lodash#mapValues to transform each value of the object data object. To combine all objects with the same key values, you can use lodash#mergeWith 与回调测试结合使用，以评估正在转换的键是否会被评估。

const result = _.mapValues(data, collection => 
  _.mergeWith({}, ...collection, (a = 0, b = 0, key) =>
    ['amount', 'price'].includes(key)
      ? a + b
      : void 0 // is equivalent to undefined to retain current value
  ));

const data = {
    "2018-08-01T11:00:00+02:00": [
        {
            "BHKW": {
                "amount": 131,
                "price": 85
            },
            "FALLBACK": {
                "amount": 84,
                "price": 1
            }
        },
        {
            "BHKW": {
                "amount": 307,
                "price": 58
            },
            "PV": {
                "amount": 4,
                "price": 60
            }
        }
    ],
    "2018-08-01T12:00:00+02:00": [
        {
            "BHKW": {
                "amount": 288,
                "price": 59
            },
            "PV": {
                "amount": 742,
                "price": 73
            }
        },
        {
            "BHKW": {
                "amount": 250,
                "price": 49
            },
            "PV": {
                "amount": 507,
                "price": 98
            }
        },
        {
            "PV": {
                "amount": 368,
                "price": 22
            },
            "BHKW": {
                "amount": 357,
                "price": 73
            }
        },
        {
            "FALLBACK": {
                "amount": 135,
                "price": 62
            },
            "BHKW": {
                "amount": 129,
                "price": 93
            }
        }
    ]
};

const result = _.mapValues(data, collection => 
  _.mergeWith({}, ...collection, (a = 0, b = 0, key) =>
    ['amount', 'price'].includes(key)
      ? a + b
      : void 0 // is equivalent to undefined to retain current value
  ));
  
console.log(result);

.as-console-wrapper{min-height:100%;top:0}

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.10/lodash.min.js"></script>

Answer 3

另一种方法（虽然不像已经发布的 _.merge 方法那么优雅）是 _.mapValues/_.reduce/_.assignWith or _.extendWith:

var data = { "2018-08-01T11:00:00+02:00": [{ "BHKW": { "amount": 131, "price": 85 }, "FALLBACK": { "amount": 84, "price": 1 } }, { "BHKW": { "amount": 307, "price": 58 }, "PV": { "amount": 4, "price": 60 } } ], "2018-08-01T12:00:00+02:00": [{ "BHKW": { "amount": 288, "price": 59 }, "PV": { "amount": 742, "price": 73 } }, { "BHKW": { "amount": 250, "price": 49 }, "PV": { "amount": 507, "price": 98 } }, { "PV": { "amount": 368, "price": 22 }, "BHKW": { "amount": 357, "price": 73 } }, { "FALLBACK": { "amount": 135, "price": 62 }, "BHKW": { "amount": 129, "price": 93 } } ] }

var result =
  _.mapValues(data, (x) =>
    _.reduce(x, (r, c) =>
      _.assignWith(r, c, (o, s) =>
        o && s ? ({ amount: o.amount + s.amount, price: o.price + s.price }) : {...o, ...s})
    )
  )

console.log(result)

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.10/lodash.min.js"></script>

javascript 减少数组中对象的多个键

javascript reduce over multiple keys of objects in an array

javascript

arrays

reduce

underscore.js

lodash