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问从对象数组中获取学生的出现情况
EN

Stack Overflow用户

提问于 2022-04-20 23:08:55

回答 5查看 64关注 0票数 0

我有一群学生：

var studentsArray = [{
    "studentId": "1",
    "courses": ["A", "A", "B", "D", "A"],
    "classPeriods": ["Chemistry", "Chemistry", "Maths"]
  },
  {
    "studentId": "1",
    "courses": ["E", "F", "E"],
    "classPeriods": ["Biology", "Chemistry", "Biology"]
  },
  {
    "studentId": "1",
    "courses": ["A", "D", "D"],
    "classPeriods": ["Computer Science", "Computer Scienc", "Biology", "Biology"]
  },
  {
    "studentId": "1",
    "courses": ["G", "K"],
    "classPeriods": ["Computer Science", "Chemistry", "Biology", "Chemistry"]
  },
  {
    "studentId": "1",
    "courses": ["A", "B", "D"],
    "classPeriods": ["Maths", "Maths", "Biology", "Chemistry"]
  },
  {
    "studentId": "2",
    "courses": ["A", "C", "F"],
    "classPeriods": ["Arts", "Maths", "Arts", "Maths"]
  },
  {
    "studentId": "2",
    "courses": ["B", "B", "D"],
    "classPeriods": ["Arts", "Arts", "Maths", "Maths"]
  },
  {
    "studentId": "3",
    "courses": ["H", "B", "R"],
    "classPeriods": ["Biology", "Biology", "Maths", "Maths"]
  }
]

在这里，我需要学生的总事件与他们的课程和classPeriods合并。

例如：

Student 2的一个对象应该是：

{
    "studentId": "2",
    "occurrence": 2,
    "courses": ["A", "C", "F", "B", "B", "D"],
    "classPeriods": ["Arts", "Maths", "Arts", "Chemistry", "Chemistry", "Arts", "Arts", "Maths", "Maths"]
}

到目前为止，我尝试的是：

function getOccurrences(arr, key) {

  let arr2 = [];

  arr.forEach((x) => {

    if (arr2.some((val) => {
        return val[key] == x[key]
      })) {

      arr2.forEach((k) => {
        if (k[key] === x[key]) {
          k["occurrence"]++
        }
      })
    } else {

      let a = {}
      a[key] = x[key]
      a["occurrence"] = 1
      arr2.push(a);
    }
  })

  return arr2
}


var studentsArray = [{
    "studentId": "1",
    "courses": ["A", "A", "B", "D", "A"],
    "classPeriods": ["Chemistry", "Chemistry", "Maths"]
  },
  {
    "studentId": "1",
    "courses": ["E", "F", "E"],
    "classPeriods": ["Biology", "Chemistry", "Biology"]
  },
  {
    "studentId": "1",
    "courses": ["A", "D", "D"],
    "classPeriods": ["Computer Science", "Computer Scienc", "Biology", "Biology"]
  },
  {
    "studentId": "1",
    "courses": ["G", "K"],
    "classPeriods": ["Computer Science", "Chemistry", "Biology", "Chemistry"]
  },
  {
    "studentId": "1",
    "courses": ["A", "B", "D"],
    "classPeriods": ["Maths", "Maths", "Biology", "Chemistry"]
  },
  {
    "studentId": "2",
    "courses": ["A", "C", "F"],
    "classPeriods": ["Arts", "Maths", "Arts", "Maths"]
  },
  {
    "studentId": "2",
    "courses": ["B", "B", "D"],
    "classPeriods": ["Arts", "Arts", "Maths", "Maths"]
  },
  {
    "studentId": "3",
    "courses": ["H", "B", "R"],
    "classPeriods": ["Biology", "Biology", "Maths", "Maths"]
  }
]

getOccurrences(studentsArray, "studentId");

现在我面临的问题是，它没有返回对象的所有属性，也没有合并course和classPeriods的数组。

我能得到一些帮助吗？

javascript

arrays

object

回答 5

Stack Overflow用户

发布于 2022-04-20 23:42:06

这就像是一个简化的教科书样例，但是您可以使用任何类型的循环，最好是使用Map来跟踪id聚合数据对。然后它的values()可以得到实际结果：

var studentsArray = [{
    "studentId": "1",
    "courses": ["A", "A", "B", "D", "A"],
    "classPeriods": ["Chemistry", "Chemistry", "Maths"]
  },
  {
    "studentId": "1",
    "courses": ["E", "F", "E"],
    "classPeriods": ["Biology", "Chemistry", "Biology"]
  },
  {
    "studentId": "1",
    "courses": ["A", "D", "D"],
    "classPeriods": ["Computer Science", "Computer Scienc", "Biology", "Biology"]
  },
  {
    "studentId": "1",
    "courses": ["G", "K"],
    "classPeriods": ["Computer Science", "Chemistry", "Biology", "Chemistry"]
  },
  {
    "studentId": "1",
    "courses": ["A", "B", "D"],
    "classPeriods": ["Maths", "Maths", "Biology", "Chemistry"]
  },
  {
    "studentId": "2",
    "courses": ["A", "C", "F"],
    "classPeriods": ["Arts", "Maths", "Arts", "Maths"]
  },
  {
    "studentId": "2",
    "courses": ["B", "B", "D"],
    "classPeriods": ["Arts", "Arts", "Maths", "Maths"]
  },
  {
    "studentId": "3",
    "courses": ["H", "B", "R"],
    "classPeriods": ["Biology", "Biology", "Maths", "Maths"]
  }
];

let stuff=[...studentsArray.reduce((res,student)=>{
  if(!res.has(student.studentId))
    res.set(student.studentId,{...student,occurrences:1});
  else{
    let s=res.get(student.studentId);
    s.courses=s.courses.concat(student.courses);
    s.classPeriods=s.classPeriods.concat(student.classPeriods);
    s.occurrences++;
  }
  return res;
},new Map()).values()];
console.log(stuff);

对于可选/未知的内容：for...in可以循环遍历对象的(枚举)属性，Array.isArray()可以判断某物是否是数组，然后我们可以对in检查采取行动，或者将其作为新属性添加(如果它还不存在)，或者连接到现有的属性：

var studentsArray = [{
    "studentId": "1",
    "courses": ["A", "A", "B", "D", "A"],
    "classPeriods": ["Chemistry", "Chemistry", "Maths"]
  },
  {
    "studentId": "1",
    "courses": ["E", "F", "E"],
    "classPeriods": ["Biology", "Chemistry", "Biology"]
  },
  {
    "studentId": "1",
    "courses": ["A", "D", "D"],
    "classPeriods": ["Computer Science", "Computer Scienc", "Biology", "Biology"]
  },
  {
    "studentId": "1",
    "courses": ["G", "K"],
    "classPeriods": ["Computer Science", "Chemistry", "Biology", "Chemistry"]
  },
  {
    "studentId": "1",
    "courses": ["A", "B", "D"],
    "classPeriods": ["Maths", "Maths", "Biology", "Chemistry"]
  },
  {
    "studentId": "2",
    "courses": ["A", "C", "F"],
    "classPeriods": ["Arts", "Maths", "Arts", "Maths"]
  },
  {
    "studentId": "2",
    "courses": ["B", "B", "D"],
    "classPeriods": ["Arts", "Arts", "Maths", "Maths"]
  },
  {
    "studentId": "3",
    "courses": ["H", "B", "R"],
    "classPeriods": ["Biology", "Biology", "Maths", "Maths"]
  },
  {
    "studentId": "4",
    "courses": ["H", "B", "R"],
  },
  {
    "studentId": "4",
    "classPeriods": ["Biology", "Biology", "Maths", "Maths"]
  }
];

let stuff=[...studentsArray.reduce((res,student)=>{
  if(!res.has(student.studentId))
    res.set(student.studentId,{...student,occurrences:1});
  else{
    let s=res.get(student.studentId);
    for(let prop in student)
      if(Array.isArray(student[prop]))
        s[prop]=prop in s?s[prop].concat(student[prop]):student[prop];
    s.occurrences++;
  }
  return res;
},new Map()).values()];
console.log(stuff);

看看4如何具有与3相同的数组内容，但是数组来自于两个不同的事件(当然，出现的次数是2)。

票数 1

Stack Overflow用户

发布于 2022-04-20 23:44:11

无需创建a对象..。您可以先将occurrence附加到x，然后再按它。

function getOccurrences(arr, key) {
  let arr2 = [];

  arr.forEach((x) => {

    if (arr2.some((val) => {
        return val[key] == x[key]
      })) {

      arr2.forEach((k) => {
        if (k[key] === x[key]) {
          k["occurrence"]++
        }
      })
    } else {

      // let a = {}
      // a[key] = x[key]
      // a["occurrence"] = 1
      // arr2.push(a);
      x["occurrence"] = 1;   // <-----
      arr2.push(x);          // <-----
    }
  })

  return arr2
}


var studentsArray = [{
    "studentId": "1",
    "courses": ["A", "A", "B", "D", "A"],
    "classPeriods": ["Chemistry", "Chemistry", "Maths"]
  },
  {
    "studentId": "1",
    "courses": ["E", "F", "E"],
    "classPeriods": ["Biology", "Chemistry", "Biology"]
  },
  {
    "studentId": "1",
    "courses": ["A", "D", "D"],
    "classPeriods": ["Computer Science", "Computer Scienc", "Biology", "Biology"]
  },
  {
    "studentId": "1",
    "courses": ["G", "K"],
    "classPeriods": ["Computer Science", "Chemistry", "Biology", "Chemistry"]
  },
  {
    "studentId": "1",
    "courses": ["A", "B", "D"],
    "classPeriods": ["Maths", "Maths", "Biology", "Chemistry"]
  },
  {
    "studentId": "2",
    "courses": ["A", "C", "F"],
    "classPeriods": ["Arts", "Maths", "Arts", "Maths"]
  },
  {
    "studentId": "2",
    "courses": ["B", "B", "D"],
    "classPeriods": ["Arts", "Arts", "Maths", "Maths"]
  },
  {
    "studentId": "3",
    "courses": ["H", "B", "R"],
    "classPeriods": ["Biology", "Biology", "Maths", "Maths"]
  }
]

let result = getOccurrences(studentsArray, "studentId");

console.log(result);

票数 1

Stack Overflow用户

发布于 2022-04-21 00:13:34

您可以使用Array#reduce和Array#map，如下所示：

注意到：这结合了所有studentId值的数据；我误解了这个问题。现在我很清楚，您希望函数返回一个ID的结果。参见下一个演示。

const 
studentsArray = [{ "studentId": "1", "courses": ["A", "A", "B", "D", "A"], "classPeriods": ["Chemistry", "Chemistry", "Maths"] }, { "studentId": "1", "courses": ["E", "F", "E"], "classPeriods": ["Biology", "Chemistry", "Biology"] }, { "studentId": "1", "courses": ["A", "D", "D"], "classPeriods": ["Computer Science", "Computer Scienc", "Biology", "Biology"] }, { "studentId": "1", "courses": ["G", "K"], "classPeriods": ["Computer Science", "Chemistry", "Biology", "Chemistry"] }, { "studentId": "1", "courses": ["A", "B", "D"], "classPeriods": ["Maths", "Maths", "Biology", "Chemistry"] }, { "studentId": "2", "courses": ["A", "C", "F"], "classPeriods": ["Arts", "Maths", "Arts", "Maths"] }, { "studentId": "2", "courses": ["B", "B", "D"], "classPeriods": ["Arts", "Arts", "Maths", "Maths"] }, { "studentId": "3", "courses": ["H", "B", "R"], "classPeriods": ["Biology", "Biology", "Matchs", "Maths"] } ],

getOccurrences = (arr, key) => Object.entries(
  arr.reduce((acc,cur) => 
    acc[cur[key]] ? 
    ({...acc, [cur[key]]: {
        occurrence: acc[cur[key]].occurrence + 1,
        courses: acc[cur[key]].courses.concat(cur.courses),
        classPeriods: acc[cur[key]].classPeriods.concat(cur.classPeriods)
     }}) :
    ({...acc, [cur[key]]: {
        occurrence: 1,
        courses:cur.courses, 
        classPeriods:cur.classPeriods
    }}), {}
  )
)
.map(
    ([studentId,courseInfo]) =>
    ({studentId, ...courseInfo})
);

console.log( getOccurrences(studentsArray,"studentId") );

单ID

本演示中的函数返回studentId的一个值的结果，该值按您的意愿作为key提供：

const 
studentsArray = [{ "studentId": "1", "courses": ["A", "A", "B", "D", "A"], "classPeriods": ["Chemistry", "Chemistry", "Maths"] }, { "studentId": "1", "courses": ["E", "F", "E"], "classPeriods": ["Biology", "Chemistry", "Biology"] }, { "studentId": "1", "courses": ["A", "D", "D"], "classPeriods": ["Computer Science", "Computer Scienc", "Biology", "Biology"] }, { "studentId": "1", "courses": ["G", "K"], "classPeriods": ["Computer Science", "Chemistry", "Biology", "Chemistry"] }, { "studentId": "1", "courses": ["A", "B", "D"], "classPeriods": ["Maths", "Maths", "Biology", "Chemistry"] }, { "studentId": "2", "courses": ["A", "C", "F"], "classPeriods": ["Arts", "Maths", "Arts", "Maths"] }, { "studentId": "2", "courses": ["B", "B", "D"], "classPeriods": ["Arts", "Arts", "Maths", "Maths"] }, { "studentId": "3", "courses": ["H", "B", "R"], "classPeriods": ["Biology", "Biology", "Matchs", "Maths"] } ],

getOccurrences = (arr, key) => {
    let d = arr.filter(({studentId}) => studentId === key);
    return {
        studentId: key,
        occurrence: d.length,
        courses: d.flatMap(({courses}) => courses),
        classPeriods: d.flatMap(({classPeriods}) => classPeriods)
    }
};

console.log( getOccurrences(studentsArray,"1") );

票数 1

页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持

原文链接：

https://stackoverflow.com/questions/71947074

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