应用程序脚本：映射未将预期值返回到数组

Question

我有一个对象数组，看起来像：

var objArray = [
  {
    " #": "4596",
    " E": "Yes",
    " Date": "06/12/20",
    " County": "Los Angeles County",
    " State": "California",
    " Acres": "2.49",
    " Eager": "Low",
  },
  {
    " #": "4588",
    " E": "Yes",
    " Date": "06/11/20",
    " County": "Towns County",
    " State": "Georgia",
    " Acres": "3.00",
    " Eager": "High",
  },
  ....
];

我正在尝试将索引数组 ('#') 放在一起；

到目前为止我有：

let indexes = objArray.forEach(function (rowObj) {
  Object.keys(rowObj).map(function (key) {
    if (key.includes("#")) {
      var v = rowObj[key];
      Logger.log(v); // abc
      return v;
    }
  });
});

Logger.log(indexes); // abc

输出：

[20-06-13 20:43:33:320 EDT] 4547
[20-06-13 20:43:33:324 EDT] 4546
[20-06-13 20:43:33:329 EDT] 4545
[20-06-13 20:43:33:450 EDT] 4543
[20-06-13 20:43:33:453 EDT] 4542
[20-06-13 20:43:33:456 EDT] 4540
[20-06-13 20:43:33:459 EDT] 4538

这正在生产：

[20-06-13 20:43:33:462 EDT] null

我做错了什么？

Answer 1

作为补充回答：

您可以更简单、更快速地完成此操作。

const values = [
  { " #": "4596", " E": "Yes"},
  { " #": "4597", " E": "No"},
  { " #": "4598", " E": "Maybe"},
]

const indices = values.map(({ " #" : id }) => id);

console.log(indices);

请注意，对map() 方法的回调应该是确定性的，以获得一致的结果。

实际问题

查看有关 forEach() 方法的文档 - 它旨在产生副作用，因此返回 void（字面上没有值），因此是最后一个 Logger.log(indexes); 问题。

有用的链接

1. map() 方法reference
2. 箭头函数guide
3. forEach() 方法 reference

Answer 2

如果您要查找的键始终是#，并且如果它存在于所有对象中，您可以使用reduce 简化逻辑。请看下面的例子

const objArray = [
  {
    " #": "4596",
    " E": "Yes",
    " Date": "06/12/20",
    " County": "Los Angeles County",
    " State": "California",
    " Acres": "2.49",
    " Eager": "Low",
  },
  {
    " #": "4588",
    " E": "Yes",
    " Date": "06/11/20",
    " County": "Towns County",
    " State": "Georgia",
    " Acres": "3.00",
    " Eager": "High",
  },
];

const output = objArray.reduce(
  (previousValue, currentValue) => [...previousValue, currentValue[" #"]],
  []
);

console.log(output)

更新 0

reduce 在需要压缩数组内容时使用它，它的操作与filter 和map 非常相似，因为它们使用了一个回调函数，在数组的每个条目中执行，不同之处在于是它减少了您在每次迭代中更新的 initialValue 参数。

例如，这是相同的版本，没有允许您使用箭头函数的快捷方式，previousValue 对应于初始值，currentValue 对应于每次迭代中的对象。所以在每次迭代中你spreadpreviousValue 的内容并获取并附加 currentValue 的# 属性的值

运行示例，以便在每次迭代中查看 previousValue 的值

const objArray = [
  {
    " #": "4596",
    " E": "Yes",
    " Date": "06/12/20",
    " County": "Los Angeles County",
    " State": "California",
    " Acres": "2.49",
    " Eager": "Low",
  },
  {
    " #": "4588",
    " E": "Yes",
    " Date": "06/11/20",
    " County": "Towns County",
    " State": "Georgia",
    " Acres": "3.00",
    " Eager": "High",
  },
];

const output = objArray.reduce((previousValue, currentValue) => {
  console.log(previousValue);
  previousValue = [...previousValue, currentValue[" #"]];

  return previousValue;
}, []);

console.log(output);

post 是我第一次读到关于 reduce 的内容，它以实用和简单的方式解释了这个概念。我推荐你阅读。干杯

Answer 3

我认为你在循环中间返回是问题所在。除此之外没关系。

这对我有用：

function functest() {
  var objArray =[{" #":"4596"," E":"Yes"," Date":"06/12/20"," County":"Los Angeles County"," State":"California"," Acres":"2.49"," Eager":"Low"},
                 {" #":"4588"," E":"Yes"," Date":"06/11/20"," County":"Towns County"," State":"Georgia"," Acres":"3.00"," Eager":"High"},
                 {" #":"4596"," E":"Yes"," Date":"06/12/20"," County":"Los Angeles County"," State":"California"," Acres":"2.49"," Eager":"Low"},
                 {" #":"4588"," E":"Yes"," Date":"06/11/20"," County":"Towns County"," State":"Georgia"," Acres":"3.00"," Eager":"High"},
                 {" #":"4596"," E":"Yes"," Date":"06/12/20"," County":"Los Angeles County"," State":"California"," Acres":"2.49"," Eager":"Low"},
                 {" #":"4588"," E":"Yes"," Date":"06/11/20"," County":"Towns County"," State":"Georgia"," Acres":"3.00"," Eager":"High"},
                 {" #":"4596"," E":"Yes"," Date":"06/12/20"," County":"Los Angeles County"," State":"California"," Acres":"2.49"," Eager":"Low"},
                 {" #":"4588"," E":"Yes"," Date":"06/11/20"," County":"Towns County"," State":"Georgia"," Acres":"3.00"," Eager":"High"}];
  var oA=[];
  let indexes=objArray.forEach(function(rowObj) {
    Object.keys(rowObj).map(function(key) {
      if (key.includes('#') ) {
        var v = rowObj[key];
        oA.push(v);
      }
    });
  });
  Logger.log(oA);
}//[4596, 4588, 4596, 4588, 4596, 4588, 4596, 4588]