Array.filter 返回空数组答案

【问题标题】：Array.filter is returning empty arrayArray.filter 返回空数组
【发布时间】：2019-09-13 09:50:15
【问题描述】：

我正在尝试根据日期获取失败详细信息。为此，我正在应用 array.filter 但它返回的是空数组。

下面是我的数组：

value:[{
  "Date": "02/04/2019",
  "Total": "1000",
  "Success": "850",
  "Failure": "150",
  "FailureDeatils": [{
      "Reason": "Reason1",
      "Count": 2
    },
    {
      "Reason": "Reason2",
      "Count": 6
    }
  ]
}, {
  "Date": "03/04/2019",
  "Total": "800",
  "Success": "750",
  "Failure": "150",
  "FailureDeatils": [{
    "Reason": "Reason1",
    "Count": 3
  }, {
    "Reason": "Reason2",
    "Count": 1
  }]
}]

如果我将日期设为 02/04/2019，它应该返回以下内容：

{
  "FailureDeatils": [{
      "Reason": "Reason1",
      "Count": 2
    },
    {
      "Reason": "Reason2",
      "Count": 6
    }
  ]
}

我正在使用下面的 array.filter 方法：

var filtered = value.filter(isPresent);
function isPresent(value) {
  return value == 02/04/2019;
}

这是返回空数组。

谁能帮我弄清楚我哪里出错了？

【问题讨论】：

return value.Date == "02/04/2019"; 也许？
什么是isPresent？请分享您使用 isPresent 申请的条件
is Present 只不过是下面写的函数
好的，我已经根据您的代码添加了答案。在代码中实现之前，您也可以在浏览器控制台上对其进行测试。
如果对您有用，请为该问题投票。谢谢！

标签： javascript arrays date object filtering

【解决方案1】：

在您的函数isPresent 中，value 是数组中的每个对象

你正在将整个对象与一个值进行比较

你需要做的是比较那个对象的对象属性

function isPresent(value) {
    return value.Date == "02/04/2019";
}

【讨论】：

谢谢！！我现在可以获取全部数据，但我只需要其中的失败详细信息

【解决方案2】：

var filtered = value.filter(function(a){
                   return a.Date === "02/04/2019";
               });

【讨论】：

02/04/2019 将在此处计算，请参阅console.log(02/04/2019) 的结果

【解决方案3】：

您需要检查value.Date 而不是value，因为value 或回调参数将保存来自array 的整个迭代object：

function isPresent(value) {
  return value.Date && value.Date == "02/04/2019";
}

要从过滤后的object 中仅获取FailureDeatils，您可以映射 Array#map() method 过滤后的结果：

var filtered = data.filter(isPresent).map(o => { return {"FailureDeatils": o.FailureDeatils}});

注意：

确保将"02/04/2019"包裹在""之间，这样它就可以被评估为string并正确比较，否则将被计算并视为Number并给出错误的过滤结果。
避免对数组使用相同的变量名value 两次用于回调参数，以提高代码的可读性。

演示：

var data = [{
  "Date": "02/04/2019",
  "Total": "1000",
  "Success": "850",
  "Failure": "150",
  "FailureDeatils": [{
      "Reason": "Reason1",
      "Count": 2
    },
    {
      "Reason": "Reason2",
      "Count": 6
    }
  ]
}, {
  "Date": "03/04/2019",
  "Total": "800",
  "Success": "750",
  "Failure": "150",
  "FailureDeatils": [{
    "Reason": "Reason1",
    "Count": 3
  }, {
    "Reason": "Reason2",
    "Count": 1
  }]
}]



var filtered = data.filter(isPresent).map(e => { return {"FailureDeatils": e.FailureDeatils}});

function isPresent(value) {
  return value.Date && value.Date == "02/04/2019";
}

console.log(filtered);

【讨论】：

【解决方案4】：

你应该这样做 -

const value = [{
  "Date": "02/04/2019",
  "Total": "1000",
  "Success": "850",
  "Failure": "150",
  "FailureDeatils": [{
      "Reason": "Reason1",
      "Count": 2
    },
    {
      "Reason": "Reason2",
      "Count": 6
    }
  ]
}, {
  "Date": "03/04/2019",
  "Total": "800",
  "Success": "750",
  "Failure": "150",
  "FailureDeatils": [{
    "Reason": "Reason1",
    "Count": 3
  }, {
    "Reason": "Reason2",
    "Count": 1
  }]
}]

const filtered = value.filter((x) => x.Date === "02/04/2019");

【讨论】：

【解决方案5】：

const value = [{
      "Date": "02/04/2019",
      "Total": "1000",
      "Success": "850",
      "Failure": "150",
      "FailureDeatils": [{
          "Reason": "Reason1",
          "Count": 2
        },
        {
          "Reason": "Reason2",
          "Count": 6
        }
      ]
    }, {
      "Date": "03/04/2019",
      "Total": "800",
      "Success": "750",
      "Failure": "150",
      "FailureDeatils": [{
        "Reason": "Reason1",
        "Count": 3
      }, {
        "Reason": "Reason2",
        "Count": 1
      }]
    }]   

    var filtered = value.filter(isPresent).map(row => {
      return {
        FailureDeatils : row.FailureDeatils
      }
    });
    function isPresent(value) {
      return value.Date === "02/04/2019";
    }

    console.log(filtered)

【讨论】：

【解决方案6】：

你可以这样做：

const value = [{"Date": "02/04/2019","Total": "1000","Success": "850","Failure": "150","FailureDeatils":[{"Reason":"Reason1","Count":2}, {"Reason":"Reason2","Count":6}]},{"Date": "03/04/2019","Total": "800","Success": "750","Failure": "150","FailureDeatils": [{"Reason":"Reason1","Count":3},{"Reason":"Reason2","Count":1}]}];
const isPresent = ({Date}) => Date === '02/04/2019';
const filtered = value.filter(isPresent);

console.log(filtered);

【讨论】：

【解决方案7】：

这是基于您的数组的工作代码。

var value = [{
  "Date": "02/04/2019",
  "Total": "1000",
  "Success": "850",
  "Failure": "150",
  "FailureDeatils": [{
      "Reason": "Reason1",
      "Count": 2
    },
    {
      "Reason": "Reason2",
      "Count": 6
    }
  ]
}, {
  "Date": "03/04/2019",
  "Total": "800",
  "Success": "750",
  "Failure": "150",
  "FailureDeatils": [{
    "Reason": "Reason1",
    "Count": 3
  }, {
    "Reason": "Reason2",
    "Count": 1
  }]
}];

var filtered = value.filter (isPresent).map (obj => obj.FailureDeatils);;
function isPresent (value) {
  return value.Date == "02/04/2019";
}

console.log (filtered);

【讨论】：