Array.filter 返回空数组

Question

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
  }]
}]      

如果我给出的日期为 02/04/2019，它应该返回以下内容：

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

我正在使用下面的数组过滤器方法：

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

这将返回空数组。

谁能弄清楚我哪里出错了？

Answer 1

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);

Answer 2

在你的函数isPresent中，数组中的每个对象value

您将整个对象与一个值进行比较

您需要做的是比较该对象的对象属性

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

Answer 3

您需要

检查value.Date而不是value，因为value或回调参数将保存array中的整个迭代object：

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

要仅从过滤object中获取FailureDeatils，您可以映射 使用Array#map()方法过滤结果：

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

注意：

• 确保在""之间换行"02/04/2019"，以便可以将其评估为string并正确比较，否则它将被计算并被视为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，并且，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);

Answer 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");

Answer 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)

Answer 6

你可以做：

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);

Answer 7

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