Suma de valores de propiedad de objeto de matriz en una nueva matriz de objetos en Javascript

arrays javascript-objects

Question

Tengo una matriz de objetos donde necesito la suma de valores de propiedad de objeto en una nueva matriz de objetos,

Entrada:

var inputArray = [
  { subject: ''Maths'', marks: ''40'', noOfStudents: ''5'' },
  { subject: ''Science'', marks: ''50'', noOfStudents: ''16'' },
  { subject: ''History'', marks: ''35'', noOfStudents: ''23'' },
  { subject: ''Science'', marks: ''65'', noOfStudents: ''2'' },
  { subject: ''Maths'', marks: ''30'', noOfStudents: ''12'' },
  { subject: ''History'', marks: ''55'', noOfStudents: ''20'' },
  .
  .
  .
];

Salida que necesito,

var outputArray = [
  { subject: ''Maths'', marks: ''70'', noOfStudents: ''17'' },
  { subject: ''Science'', marks: ''115'', noOfStudents: ''18'' },
  { subject: ''History'', marks: ''95'', noOfStudents: ''43'' },
  .
  .
  .
];

Quiero suma de calificaciones y no de estudiantes de asignaturas en una nueva matriz de objetos. Habría N número de otros objetos sujetos (es decir, Geografía, Física, etc.) en la matriz de entrada.

Answer 1

Aqui tienes:

function convert(inputArray) {
    var temp = {};
    for(var i = 0; i < inputArray.length; i++) {
        var subject = inputArray[i].subject;

        // check if there is already an entry with this subject in the temp array
        if(temp.hasOwnProperty(subject)) {
            // if it is already in the list, add the marks and the noOfStudents
            temp[subject].marks = temp[subject].marks + parseInt(inputArray[i].marks, 10);
            temp[subject].noOfStudents = temp[subject].noOfStudents + parseInt(inputArray[i].noOfStudents, 10);
        }
        else {
            // if it is not yet in the list, add a new object
            temp[subject] = {
                subject: subject,
                marks: parseInt(inputArray[i].marks, 10),
                noOfStudents: parseInt(inputArray[i].noOfStudents, 10)
            }
        }
    }

    // the temporary array is based on the subject, you are however interested on the effective value object
    var result = [];
    for(var entryKey in temp) {
        result.push(temp[entryKey]);
    }

    return result;
}

Answer 2

La solución que utiliza las Array.forEach , parseInt y Object.keys :

var summed = {}, result;
inputArray.forEach(function (obj) {
    obj[''marks''] = parseInt(obj[''marks'']);
    obj[''noOfStudents''] = parseInt(obj[''noOfStudents'']);
    var subj = obj[''subject''];

    if (!summed[subj]) {
        summed[subj] = obj;
    } else {
        summed[subj][''marks''] += obj[''marks''];
        summed[subj][''noOfStudents''] += obj[''noOfStudents''];
    }
}, summed);
result = Object.keys(summed).map((k) => summed[k]);

console.log(JSON.stringify(result, 0, 4));

La salida:

[
    {
        "subject": "Maths",
        "marks": 70,
        "noOfStudents": 17
    },
    {
        "subject": "Science",
        "marks": 115,
        "noOfStudents": 18
    },
    {
        "subject": "History",
        "marks": 90,
        "noOfStudents": 43
    }
]

Answer 3

Puede hacerlo con el parámetro opcional forEach y thisArg

var inputArray = [
  { subject: ''Maths'', marks: ''40'', noOfStudents: ''5'' },
  { subject: ''Science'', marks: ''50'', noOfStudents: ''16'' },
  { subject: ''History'', marks: ''35'', noOfStudents: ''23'' },
  { subject: ''Science'', marks: ''65'', noOfStudents: ''2'' },
  { subject: ''Maths'', marks: ''30'', noOfStudents: ''12'' },
  { subject: ''History'', marks: ''55'', noOfStudents: ''20'' },
], outputArray = [];
  
inputArray.forEach(function(e) {
  if(!this[e.subject]) {
    this[e.subject] = { subject: e.subject, marks:  0, noOfStudents: 0 }
     outputArray.push(this[e.subject]);
   }
  this[e.subject].marks += Number(e.marks);
  this[e.subject].noOfStudents += Number(e.noOfStudents);
}, {});

console.log(outputArray)

Answer 4

Puede usar forEach para iterar y generar la nueva matriz

var inputArray = [
  { subject: ''Maths'', marks: ''40'', noOfStudents: ''5'' },
  { subject: ''Science'', marks: ''50'', noOfStudents: ''16'' },
  { subject: ''History'', marks: ''35'', noOfStudents: ''23'' },
  { subject: ''Science'', marks: ''65'', noOfStudents: ''2'' },
  { subject: ''Maths'', marks: ''30'', noOfStudents: ''12'' },
  { subject: ''History'', marks: ''55'', noOfStudents: ''20'' }
],
    res = [],
    key = {};

inputArray.forEach(function(v) {
  if (key.hasOwnProperty(v.subject)) { // check subject already added by using key object
    res[key[v.subject]].marks += Number(v.marks); //incase already exist parse number and add
    res[key[v.subject]].noOfStudents += Number(v.noOfStudents);
  } else {
    key[v.subject] = res.length; // create index entry in key object
    res.push({ // push the value 
      ''subject'': v.subject,
      ''marks'': Number(v.marks),
      ''noOfStudents'': Number(v.noOfStudents)
    })
    // if you pushed the original object then the original array also will get updated while adding the mark, so never push the refernce
  }
})

console.log(res);

Usando el método forEach

var inputArray = [
  { subject: ''Maths'', marks: ''40'', noOfStudents: ''5'' },
  { subject: ''Science'', marks: ''50'', noOfStudents: ''16'' },
  { subject: ''History'', marks: ''35'', noOfStudents: ''23'' },
  { subject: ''Science'', marks: ''65'', noOfStudents: ''2'' },
  { subject: ''Maths'', marks: ''30'', noOfStudents: ''12'' },
  { subject: ''History'', marks: ''55'', noOfStudents: ''20'' }
],
    key = {};

res=inputArray.reduce(function(arr,v) {
  if (key.hasOwnProperty(v.subject)) { // check subject already added by using key object
    arr[key[v.subject]].marks += Number(v.marks); //incase already exist parse number and add
    arr[key[v.subject]].noOfStudents += Number(v.noOfStudents);
  } else {
    key[v.subject] = arr.length; // create index entry in key object
    arr.push({ // push the value 
      ''subject'': v.subject,
      ''marks'': Number(v.marks),
      ''noOfStudents'': Number(v.noOfStudents)
    })
    // if you pushed the original object then the original array also will get updated while adding the mark, so never push the refernce     
  }
  return arr;
},[])

console.log(res);

FYI: puede evitar el objeto key utilizando el método find() , pero el rendimiento puede ser un poco más lento.

Answer 5

Solo otra propuesta con un objeto como tabla hash.

var inputArray = [{ subject: ''Maths'', marks: ''40'', noOfStudents: ''5'' }, { subject: ''Science'', marks: ''50'', noOfStudents: ''16'' }, { subject: ''History'', marks: ''35'', noOfStudents: ''23'' }, { subject: ''Science'', marks: ''65'', noOfStudents: ''2'' }, { subject: ''Maths'', marks: ''30'', noOfStudents: ''12'' }, { subject: ''History'', marks: ''55'', noOfStudents: ''20'' }],
    outputArray = [];
inputArray.forEach(function (a) {
    if (!this[a.subject]) {
        this[a.subject] = { subject: ''Maths'', marks: ''0'', noOfStudents: ''0'' };
        outputArray.push(this[a.subject]);
    }
    this[a.subject].marks = (+this[a.subject].marks + +a.marks).toString();
    this[a.subject].noOfStudents = (+this[a.subject].noOfStudents + +a.noOfStudents).toString();
}, Object.create(null));

console.log(outputArray);