javascript - 按相同元素对数组对象求和

Question

var data = [
   {id: 1, quantity: 10, category: 'A'},
   {id: 2, quantity: 20, category: 'B'},
   {id: 1, quantity: 30, category: 'A'},
   {id: 1, quantity: 30, category: 'Z'},
   {id: 2, quantity: 40, category: 'D'}
];

var totalPerType = {};
for (var i = 0, len = data.length; i < len; ++i) {
    totalPerType[data[i].id] = totalPerType[data[i].id] || 0;
    totalPerType[data[i].id] += data[i].quantity;
}
var out = _.map(totalPerType, function (id, quantity) {
    return {'id': id, 'quantity': quantity};
});
console.log(out);

我的代码目前对具有相同 ID 的对象的数量求和。它返回

[ {id:1, quantity:70}, {id:2, quantity:60} ]

如何根据 id 和类别获取对象的总和？

例如，我需要这样的输出:

[ 
     {id:1, quantity:40, category:A}, 
     {id:1, quantity:30, category:Z}, 
     {id:2, quantity:20, category:B}, 
     {id:, quantity:40, category:D} 
]

我想要纯 javascript 和下划线的答案。

Answer 1

使用普通 js。

var tmp = {}

data.forEach(function (item) {
    var tempKey = item.id + item.category;
    if (!tmp.hasOwnProperty(tempKey)) {
        tmp[tempKey] = item;
    } else {
        tmp[tempKey].quantity += item.quantity;
    }
});

var results = Object.keys(tmp).map(function(key){
    return tmp[key];
});

请注意，这将更改原始数据中的对象。如果不需要的话，在添加到 tmp 对象时需要复制 item

var data = [
   {id: 1, quantity: 10, category: 'A'},
   {id: 2, quantity: 20, category: 'B'},
   {id: 1, quantity: 30, category: 'A'},
   {id: 1, quantity: 30, category: 'Z'},
   {id: 2, quantity: 40, category: 'D'}
];

var tmp = {}

data.forEach(function (item) {
    var tempKey = item.id + item.category;
    if (!tmp.hasOwnProperty(tempKey)) {
        tmp[tempKey] = item;
    } else {
        tmp[tempKey].quantity += item.quantity
    }
});

var results = Object.keys(tmp).map(function(key){
    return tmp[key];
});

document.body.innerHTML ='<pre>' + JSON.stringify(results,null,4) +'</pre>';