Insert new element in an array of object and sort the array

Question

I have an array of objects that contains the name and marks of students. like below

How can I calculate the 'average' marks each student has and compare the 'average' marks to get the top student. I don’t want to use ES6

var Students = [{
    name: "Bob",
    marks: [78, 80, 89, 90, 68]
  },
  {
    name: "Alin",
    marks: [87, 60, 59, 70, 68]
  },
  {
    name: "bikash",
    marks: [82, 60, 79, 60, 80]
  }
];


var average;
var newArray = [];
for (let i = 0; i < Students.length; i++) {
  var marks = Students[i]["marks"];
  var total = 0;
  console.log(marks);
  for (var j = 0; j < marks.length; j++) {
    total += marks[j];
  }
  average = total / marks.length;
  newArray.push(average)
  var msg = Students[i]["name"] + " has average mark: " + average;
  console.log(msg)

}

console.log(newArray)

I want to insert the average numbers in an object along with the names like [{name: "Bob", average:89.4},{name: "Alin", average:87.2},{name: "Bikash", average:89.4} ] and sort the object.

Finally, I want to have console.log as Bob is the Top student OR Alin and Bob are the brightest students (in case both of them have the same average number)

Answer 1

I have used non ES6 functins, instead traditional for loop and other. Please, find answers for your three questions:

• Creating a list/array of object in this format: [ { name: 'Alin', average: 68.8 }, ..]

• Sorting a list/array with average value

• Getting students with the highest average grade.

       const Students = [{
       name: 'Bob',
       marks: [78, 80, 89, 90, 68],
   },
       {
           name: 'Alin',
           marks: [87, 60, 59, 70, 68],
       },
       {
           name: 'bikash',
           marks: [82, 60, 79, 60, 80],
       },
       {
           name: 'Doston',
           marks: [78, 80, 89, 90, 68],
       },
   ];
  
   var average;
   var data = [];
   for (var i = 0; i < Students.length; i++){
       var marks = Students[i]["marks"];
       var total = 0;
       console.log(marks);
       for (var j = 0; j < marks.length; j++ ) {
           total += marks[j];
       }
       average = total / marks.length;
  
       var msg = Students[i]["name"] + " has average mark: " + average;
       console.log(msg);
  
       // Answer for the first question:
       var item = {"name": Students[i]["name"], "average": average};
       data.push(item);
  
   }
  
   function compareAndSort(a,b) {
       return parseInt(a.average, 10) - parseInt(b.average, 10);
   }
  
   data.sort(compareAndSort);
  
   // Answer for the second question: sort [ { name: 'Alin', average: 68.8 }, ..]
   console.log(data);
  
   // Answer for the third question - getting students who has highest mark is last since it is sorted
   var bestStudent = data[data.length - 1];
   console.log(bestStudent.name + " has got the highest mark: " + bestStudent.average);
  
   var bestStudents = [bestStudent];
  
   // check if there is only one person with this highest mark
   for (var i = 0; i < data.length; i ++) {
       if (data[i].average >= bestStudent.average && data[i].name !== bestStudent.name) {
           bestStudents.push(data[i]);
       }
   }
  
   // all best students
   console.log(bestStudents);
  

I have added some data to the JSON input, so that you get two best students

Answer 2

Instead of using loops, I used the built-in array methods, which tend to be much more readable (although they would be a lot more readable if you used ES6 syntax).

I use the Array.prototype.map method to convert the list of marks into the average. In order to find this average, I use Array.prototype.reduce to add up all of the values, and then I divide by the length of the marks array. I then sort the array using Array.prototype.sort.

In order to get the top students, I use Array.prototype.filter in order to select only the students will average marks equal to the top average mark, which since the averages array is sorted, will be averages[0].average.

var Students = [
  {
    name: "Bob",
    marks: [78, 80, 89, 90, 68]
  },
  {
    name: "Alin",
    marks: [87, 60, 59, 70, 68]
  },
  {
    name: "bikash",
    marks: [82, 60, 79, 60, 80]
  }
];

var averages = Students.map(function(student) {
  return {
    name: student.name,
    average: student.marks.reduce(function(a, b) {
      return a + b;
    }) / student.marks.length
  };
}).sort(function(a, b) {
  return b.average - a.average;
});

var top_students = averages.filter(function(student, _i, arr) {
  return student.average === arr[0].average;
});

console.log("Averages:");
console.log(averages);

console.log("Top Students:\n");
console.log(top_students);

Answer 3

var Students = [{
    name: "Bob",
    marks: [78, 80, 89, 90, 68]
  },
  {
    name: "Alin",
    marks: [87, 60, 59, 70, 68]
  },
  {
    name: "bikash",
    marks: [82, 60, 79, 60, 80]
  }
];

console.log (
  Students.map (
    student => (
      {
        name: student.name,
        average:
          student.marks.reduce ((a, m) => a + m, 0) /
          student.marks.length
      }
    )
  ).sort ((a, b) => b.average - a.average)
);

Answer 4

You don't need an additional array. In theory, calling sort is less efficient than to gather the best student(s) during your loop.

So:

var students = [{name: "Bob",marks: [78,80,89,90,68] },{name: "Alin",marks: [87,60,59,70,68]},{name: "bikash",marks: [82,60,79,60,80]}];

var topAverage = -1; 
var topStudents = [];
var newArray = [];
for (let i = 0; i < students.length; i++){
    var marks = students[i].marks;
    var total = 0;
    for (var j = 0; j < marks.length; j++ ) {
        total += marks[j];
    }
    var average = total / marks.length;
    // Keep topAverage & topStudents up to date:
    if (average >= topAverage) {
        if (average > topAverage) {
            topStudents.length = 0; // clear previous content
            topAverage = average;
        }
        topStudents.push(students[i].name);
    }
}

console.log("Top student(s): " + topStudents + " with an average of " + topAverage);

Answer 5

Don't push the average into a new array, add it as a property of Students[i] with Students[i].average = average;.

Then you can sort the array using that property, and print the to students from the sorted array.

var Students = [{
    name: "Bob",
    marks: [78, 80, 89, 90, 68]
  },
  {
    name: "Alin",
    marks: [87, 60, 59, 70, 68]
  },
  {
    name: "bikash",
    marks: [82, 60, 79, 60, 80]
  }
];


var average;
for (let i = 0; i < Students.length; i++) {
  var marks = Students[i]["marks"];
  var total = 0;
  for (var j = 0; j < marks.length; j++) {
    total += marks[j];
  }
  average = total / marks.length;
  Students[i].average = average;
  var msg = Students[i]["name"] + " has average mark: " + average;
  console.log(msg)

}
Students.sort((s1, s2) => s2.average - s1.average);
var topAvg = Students[0].average;
var topStudents = Students.filter(s => s.average == topAvg).map(s => s.name).join(", ");
console.log(`Top Students are ${topStudents} with mark ${topAvg}`);