从一个数组创建2个数组ecmascript 2015

Question

我有一个数组，我需要能够从它得到2个数组。我需要这两个数组作为图表。图表组件需要一个标签数组和一个总数组（每个标签）。

我还在学习新的数组方法，的forEach，地图等于是用我裸，这是数组我有：

const income = [ 
    { 
     "date": 1482233886000, 
     "name": "Company A", 
     "type": "Salary", 
     "description": "Salary jan. 2017", 
     "amount": 50.6 
    }, 
    { 
     "date": 1482406686000, 
     "name": "Company B", 
     "type": "Salary", 
     "description": "Salary jan. 2017", 
     "amount": 40.23 
    }, 
    { 
     "date": 1485171486000, 
     "name": "Company A", 
     "type": "Salary", 
     "description": "Salary feb. 2017", 
     "amount": 200.2 
    }, 
    { 
     "date": 1485344286000, 
     "name": "Company B", 
     "type": "Salary", 
     "description": "Salary feb. 2017", 
     "amount": 100.4 
    }, 
    { 
     "date": 1490655892000, 
     "name": "Company A", 
     "type": "Salary", 
     "description": "Salary mar. 2017", 
     "amount": 20 
    }, 
    { 
     "date": 1493335850000, 
     "name": "Company A", 
     "type": "Salary", 
     "description": "Salary apr. 2017", 
     "amount": 15 
    }, 
    { 
     "date": 1493335850000, 
     "name": "Company B", 
     "type": "Salary", 
     "description": "Salary apr. 2017", 
     "amount": 10 
    } 
    ]; 

为了让我这样做是为了得到独一无二的标签标签（说明）：

[...new Set(income.map(value => value.description))] 
=> ["Salary jan. 2017", "Salary feb. 2017", "Salary mar. 2017", "Salary apr. 2017"] 

这工作，但现在我想每一个描述如总量：

//[90.83, 300.6, 20, 25] 

如果可能的话，是否有人可以帮助我使用最后一个阵列和ES6风格。我想减少，但我无法得到任何的。所以我希望一个主人可以教我; D。

Answer 1

您可以缩小到一个Map中，得到的keys（）和values（）将是您的数组，并按描述进行分组和汇总。

const income = [{"date": 1482233886000,"name": "Company A","type": "Salary","description": "Salary jan. 2017","amount": 50.6},{"date": 1482406686000,"name": "Company B","type": "Salary","description": "Salary jan. 2017","amount": 40.23},{"date": 1485171486000,"name": "Company A","type": "Salary","description": "Salary feb. 2017","amount": 200.2},{"date": 1485344286000,"name": "Company B","type": "Salary","description": "Salary feb. 2017","amount": 100.4},{"date": 1490655892000,"name": "Company A","type": "Salary","description": "Salary mar. 2017","amount": 20},{"date": 1493335850000,"name": "Company A","type": "Salary","description": "Salary apr. 2017","amount": 15},{"date": 1493335850000,"name": "Company B","type": "Salary","description": "Salary apr. 2017","amount": 10}]; 
 

 
let res = income.reduce((a, b) => { 
 
    a.set(b.description, (a.get(b.description) || 0) + b.amount); 
 
    return a; 
 
}, new Map()); 
 

 
console.log([...res.values()]); // the summed amount 
 
console.log([...res.keys()]); // the description property

编辑的评论

要添加到您使用set（）映射中的项 - 在上面的例子中，我使用的说明财产作为密钥，并且添加金额。在这部分代码：

(a.get(b.description) || 0) 

基本上只是检查，如果创建的地图拥有像迭代描述的关键，如果是的话，它需要在现有量补充。 ||短路，所以如果没有现有量（a.get（b.description）未定义），则取而代之。英语不是我的第一语言 - 这里是什么，我的意思是一个简单的例子：

let m = new Map(); 
 
m.set("foo", 1); 
 
let a = m.get("foo"); 
 
console.log(a); // 1 - obvious 
 
let b = m.get("bar"); 
 
console.log(b); // undefined 
 

 
console.log(b || 0); // 0, as b is undefined, 0 is taken 
 
// in the original answer, this would be the same as 
 
if (! b) b = 0; 
 
console.log(b); 0 
 

 
let c = (b || 0) + 1; // 0 + 1 because b is undefined; 
 
console.log("c: ", c); 
 

 
let d = (a || 0) + 1; // 1 + 1 because a holds 1; 
 
console.log("d:", d);

Answer 2

另一种方法：

• 滤波器income可变摆脱重复说明
的
• 获取已过滤数组的每个元素并遍历income数组以获取具有相同的条目值然后总结它们的amount属性
• 将每个元素的总数推入新建的arr数组。

const income=[{date:1482233886e3,name:"Company A",type:"Salary",description:"Salary jan. 2017",amount:50.6},{date:1482406686e3,name:"Company B",type:"Salary",description:"Salary jan. 2017",amount:40.23},{date:1485171486e3,name:"Company A",type:"Salary",description:"Salary feb. 2017",amount:200.2},{date:1485344286e3,name:"Company B",type:"Salary",description:"Salary feb. 2017",amount:100.4},{date:1490655892e3,name:"Company A",type:"Salary",description:"Salary mar. 2017",amount:20},{date:149333585e4,name:"Company A",type:"Salary",description:"Salary apr. 2017",amount:15},{date:149333585e4,name:"Company B",type:"Salary",description:"Salary apr. 2017",amount:10}]; 
 

 
var arr = []; 
 
var sorted = [...new Set(income.map(value => value.description))]; 
 
sorted.forEach(function(v){ 
 
    var obj = {}; 
 
    var sum = 0; 
 
    income.forEach(function(c){ 
 
    if (c.description == v){ 
 
     sum += c.amount; 
 
    } 
 
    }); 
 
    obj[v] = sum; 
 
    arr.push(obj); 
 
}); 
 

 
console.log(arr);