Question

要使用react，我有一个像这样的对象数组：

   {
    _id: 1,
    items: [

              { goodName: "cake", amount: 10 },
              { goodName: "potato", amount: 11 },
              { goodName: "apple", amount: 15 }
           ]
    }
    {
    _id: 2,
    items: [

              { goodName: "cake", amount: 10 },
              { goodName: "potato", amount: 11 },
              { goodName: "apple", amount: 15 }
           ]
    }
    {
    _id: 3,
    items: [

              { goodName: "cake", amount: 10 },
              { goodName: "potato", amount: 11 },
              { goodName: "apple", amount: 15 }
           ]
    }

现在，我想循环遍历此对象数组，并返回一个数组包含每种商品的累计价值。我想使用.map()方法将其设为：

 var value = items.map(function(item) {
                var amounts = 0;
                var amount=[];
                for (var i=0; i<=myArr.length; i++) {
                    if (myArr[i] === item.name) {
                        amounts=amounts+item.amount;
                        amount.push(amounts);
                    }
                }
            })

但它不起作用。 myArr是我使用new Set()和的数组 Array.from()循环遍历goodName并返回它的方法。我不知道我用什么方法可以做到，每个人都有另一种方式吗？

Answer 1

我编写了代码来循环显示您的信息并返回每种优良类型总金额的结果。但是，需要做出一些澄清。

您问题中的信息需要用方括号括起来，因为您显示的外部对象需要是数组中的元素。
我回复了一个对象，而不是你在问题中建议的数组。这样，results就可以包含每个标记对应的项目的信息，即{good1: total1, good2: total2, ...}
我包含一个额外的（第四个）对象，只是为了表明代码在每个数组元素中既不需要相同数量的商品，也不需要相同的商品标识。

var arr = [
  {_id: 1, items: [
    {goodName: "cake",   amount: 10},
    {goodName: "potato", amount: 11},
    {goodName: "apple",  amount: 15}
  ]},
  {_id: 2, items: [
    {goodName: "cake",   amount: 10},
    {goodName: "potato", amount: 11},
    {goodName: "apple",  amount: 15}
  ]},
  {_id: 3, items: [
    {goodName: "cake",   amount: 10},
    {goodName: "potato", amount: 11},
    {goodName: "apple",  amount: 15}
  ]},
  {_id: 4, items: [
    {goodName: "potato", amount: 1000},
    {goodName: "peach",  amount: 2000}
  ]}
];

var results = {};
arr.forEach(arrElmt => {
  arrElmt.items.forEach(item => {
    results[item.goodName] = (results[item.goodName] || 0) + item.amount;
  });
});
var res = JSON.stringify(results);

console.log(res);

Answer 2

您不能仅使用地图，因为您正在累积项目的值。我会使用reduce：

const arr = [
      {_id: 1, items: [
        {goodName: "cake",   amount: 10},
        {goodName: "potato", amount: 11},
        {goodName: "apple",  amount: 15}
      ]},
      {_id: 2, items: [
        {goodName: "cake",   amount: 10},
        {goodName: "potato", amount: 11},
        {goodName: "apple",  amount: 15}
      ]},
      {_id: 3, items: [
        {goodName: "cake",   amount: 10},
        {goodName: "potato", amount: 11},
        {goodName: "apple",  amount: 15}
      ]},
      {_id: 4, items: [
        {goodName: "potato", amount: 1000},
        {goodName: "peach",  amount: 2000}
      ]}
    ];
    
    let results = [].concat.apply([], arr.map(elem => elem.items))
        .reduce((results, item) => {
            results[item.goodName] = (results[item.goodName] || 0) + item.amount;
            return results;
        }, {});
    document.write(JSON.stringify(results));

JS没有flatMap，所以[].concat.apply舞蹈有点奇怪，但任何好的图书馆都会有它。

Javascript循环一个对象数组并返回一个新数组

2 个答案: