How do I add numerical values of a JSON array object?

Question

I am trying to add these integer values from this Array object to get the sum and in turn the average.

Input: [
        {"string": "John", "integer": 7},
        {"string": "Margot", "integer": 8},
        {"string": "Jules", "integer": 4},
        {"string": "Marco", "integer": 19}
       ]

Output: 9.5

I have been able to do this function, however, I am not able to add the values from the integer into a sum variable and divide by the objectName.length. My sample code is beneath, I want to understand why it is not working?

function my_average_mark(student_grades) {
    sum = 0;
    for( i = 0; i < student_grades.length; i++){
        // console.log(student_grades[i].integer);
        sum += student_grades[i].integer;
        console.log(sum);
        
    }
    
};


all_grades = [
        {"string": "John", "integer": 7},
        {"string": "Margot", "integer": 8},
        {"string": "Jules", "integer": 4},
        {"string": "Marco", "integer": 19}
       ]
console.log(my_average_mark(all_grades));

There's no such thing as a "JSON Object" (or a "JSON array object") - Input and all_grades are arrays of objects... — Andreas
– Andreas, Commented Mar 16, 2021 at 11:16
Note you arent returning anything from your function, so the last log won't show anything — Patrick Evans
– Patrick Evans, Commented Mar 16, 2021 at 11:18
As @Nick already mentioned why it's not working the one line solution is something like this console.log(Input.reduce((n, {integer}) => n + integer, 0)/Input.length) — Akshay Katariya
– Akshay Katariya, Commented Mar 16, 2021 at 11:25
@PatrickEvans actually my last log printed out something. but it was adding up values for my integer values. Nick suggestion helped out. Thanks. — Asante Michael
– Asante Michael, Commented Mar 16, 2021 at 11:45

Karol Gaj · Accepted Answer · 2021-03-16 11:23:50Z

2

function my_average_mark(student_grades) {
    sum = 0;
    for( i = 0; i < student_grades.length; i++){
        sum += student_grades[i].integer;        
    }
    return sum / student_grades.length;
};

consider using array functions like map and reduce

function my_average_mark(student_grades) {
    sum = student_grades.map(p => p.integer).reduce((a,b) => a+b, 0)
    return sum / student_grades.length;
};

answered Mar 16, 2021 at 11:23

Karol Gaj

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Comments

Nick · Accepted Answer · 2021-03-16 21:31:25Z

1

Your code is almost right, you just need to return the sum divided by the length:

function my_average_mark(student_grades) {
  let sum = 0;
  let len = student_grades.length;
  for (let i = 0; i < len; i++) {
    sum += student_grades[i].integer;
  }
  return Math.round(sum * 10 / len) / 10;
};


all_grades = [
        {"string": "John", "integer": 7},
        {"string": "Margot", "integer": 8},
        {"string": "Jules", "integer": 4},
        {"string": "Marco", "integer": 19}
       ]
console.log(my_average_mark(all_grades));

Note you should always declare your variables using var, let or const.

edited Mar 16, 2021 at 21:31

answered Mar 16, 2021 at 11:17

Nick

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1 Comment

Nick Over a year ago

@AsanteMichael I modified your edit to use Math.round to round to 1 decimal place instead; using toFixed would mean that the function would return a string instead of a number.

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