如何將具有相同值的多個JavaScript物件轉換為一個等于這些值總和的物件？

這是我的第一篇文章，所以我會盡力做到盡可能徹底！我需要將具有相同值的多個 JavaScript 物件轉換為一個唯一的物件，每個物件中的所有其他鍵的總數。

我有一個包含不同學校物件的陣列，每個物件都有一個表示學校學生人數的值。這是我正在使用的內容：

let schools = [
  {
    school: "a",
    students: 1000,
  },
  {
    school: "b",
    students: 10000,
  },
  {
    school: "b",
    students: 400,
  },
  {
    school: "c",
    students: 10000,
  },
  {
    school: "d",
    students: 2000,
  },
  {
    school: "c",
    students: 1000,
  },
  {
    school: "d",
    students: 4000,
  },
]

我想回傳每個給定學校的單個物件陣列，以及每個給定學校物件中學生的值的總和。這是我期待的結果：

  {
    school: "a",
    students: 1000,
  },
  {
    school: "b",
    students: 10400,
  },
  {
    school: "c",
    students: 11000,
  },
  {
    school: "d",
    students: 6000,
  }
]

這是我的解決方案到目前為止的樣子：

let listOfUniqueSchools = [];
for (let i = 0; i < schools.length; i  ) {
  if (!listOfUniqueSchools.includes(schools[i].school)) {
    listOfUniqueSchools.push(schools[i].school);
  } else {
  }
}

let outputArray = [];
for (let j = 0; j < listOfUniqueSchools.length; j  ) {
  for (let k = 0; k < schools.length; k  ) {
    let totalNumberOfStudents = 0;
    if (listOfUniqueSchools[j] == schools[k].school) {
      totalNumberOfStudents  = schools[k].students;
      outputArray.push({
        school: schools[k].school,
        students: totalNumberOfStudents,
      });
    }
  }
}

這是我得到的：

[
  {
    school: "a",
    students: 1000,
  },
  {
    school: "b",
    students: 10000,
  },
  {
    school: "b",
    students: 400,
  },
  {
    school: "c",
    students: 10000,
  },
  {
    school: "c",
    students: 1000,
  },
  {
    school: "d",
    students: 2000,
  },
 
  {
    school: "d",
    students: 4000,
  },
]

有誰知道我需要改變什么來解決這個問題？

uj5u.com熱心網友回復：

此解決方案使用 for 回圈 (forEach) 來填充以學校為鍵、以學生總數為值的新物件。然后我們使用 Object.keys 方法獲取在 totals 物件中找到的學校陣列，并使用 map 函式將資料轉換為預期的輸出格式。

它比嵌套回圈要干凈得多。

const schools = [{
    school: "a",
    students: 1000,
  },
  {
    school: "b",
    students: 10000,
  },
  {
    school: "b",
    students: 400,
  },
  {
    school: "c",
    students: 10000,
  },
  {
    school: "d",
    students: 2000,
  },
  {
    school: "c",
    students: 1000,
  },
  {
    school: "d",
    students: 4000,
  },
]


const totals = {}
schools.forEach((entry) => {
  if (totals.hasOwnProperty(entry.school)) {
    totals[entry.school]  = entry.students
  } else {
    totals[entry.school] = entry.students
  }
})

const formattedTotals = Object.keys(totals).map((school) => ({
  school: school,
  students: totals[school]
}))

console.log(formattedTotals)

uj5u.com熱心網友回復：

您的代碼中的問題是該Array.push部分在內部回圈中，而它應該在外部回圈中。

outputArray.push({
    school: listOfUniqueSchools[j],
    students: totalNumberOfStudents,
});

把它移到外面它會起作用。

使用 可能更簡單Array.reduce，請參閱下面的代碼片段。

let schools = [ {    school: "a",    students: 1000,  },  {    school: "b",    students: 10000,  },{    school: "b",    students: 400,  },  {    school: "c",    students: 10000,  },  {    school: "d",    students: 2000,  },  {    school: "c",    students: 1000,  },  {    school: "d",    students: 4000,  },];


let listOfUniqueSchools = [];
for (let i = 0; i < schools.length; i  ) {
    if (!listOfUniqueSchools.includes(schools[i].school)) {
        listOfUniqueSchools.push(schools[i].school);
    } else {
    }
}

let outputArray = [];
for (let j = 0; j < listOfUniqueSchools.length; j  ) {
    let totalNumberOfStudents = 0;
    for (let k = 0; k < schools.length; k  ) {
        if (listOfUniqueSchools[j] == schools[k].school) {
            totalNumberOfStudents  = schools[k].students;
        }
    }
    outputArray.push({
        school: listOfUniqueSchools[j],
        students: totalNumberOfStudents,
    });
}

console.log(outputArray);

// or simply use array reduce

const result = schools.reduce((acc, item) => {
    const sum = acc.find(sum => sum.school === item.school);
    sum ? sum.students  = item.students : acc.push({school: item.school, students: item.students});
    return acc;
}, []);

console.log(result);

uj5u.com熱心網友回復：

我會遍歷學校并創建一個物件，其中鍵是學校（“a”、“b”、“c”等），值是學生的累計數量。

然后回圈遍歷該陣列以創建一個物件陣列，每個物件都有一個鍵“學校”和值，以及一個帶有累積值的鍵“學生”。

let schools = [
  {
    school: "a",
    students: 1000,
  },
  {
    school: "b",
    students: 10000,
  },
  {
    school: "b",
    students: 400,
  },
  {
    school: "c",
    students: 10000,
  },
  {
    school: "d",
    students: 2000,
  },
  {
    school: "c",
    students: 1000,
  },
  {
    school: "d",
    students: 4000,
  },
]

let totals = {} // Interim totals
schools.forEach( function(school) {
    // console.log(school.students, school.school)
    totals[school.school] = ( totals[school.school] ?? 0 )   school.students;
})

let results = [] // Final results
for ( const school in totals ) {
    results.push(
        {
            school: school,
            students: totals[school]
        }
    )
}

console.log(results)

/*
Array(4) [ {…}, {…}, {…}, {…} ]
?0: Object { school: "a", students: 1000 }
?1: Object { school: "b", students: 10400 }
?2: Object { school: "c", students: 11000 }
?3: Object { school: "d", students: 6000 }
?length: 4
*/

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