Sum nested array

Question

I have an array within an array of objects and I want to sum the values within the nested array.

[{BenefitType:'401k',
   Beneficiaries: [{Name: 'PersonA', Percentage: 20},
                   {Name: 'PersonB', Percentage: 30},
                   {Name: 'PersonC', Percentage: 50}]
},
 {BenefitType:'IRA',
   Beneficiaries: [{Name: 'PersonA', Percentage: 15},
                   {Name: 'PersonB', Percentage: 45},
                   {Name: 'PersonC', Percentage: 40}]
}];

I would like to sum all the percentages by their Benefit Type so that 401k = 100and IRA = 100.

I have the following code, but it gives me a grand total for percentages instead of totals for each benefit type:

var myTotal = 0;

for(var i = 0; i < data.benefit_type.length; i++) {
    for(var j=0; j < data.benefit_type[i].beneficiaries.length; j++) {
        myTotal += parseInt(data.benefit_type[i].beneficiaries[j].percentage); 
        data.benefit_type[i].percent_total = myTotal;

    } 
}

What am I missing to fix this?

Possible duplicate of Sum of array object property values in new array of objects in Javascript — Heretic Monkey
– Heretic Monkey, Commented Jun 8, 2018 at 20:47

mickl · Accepted Answer · 2018-06-08 21:14:29Z

4

You can use .forEach() to iterate through all objects and .reduce() to sum inner arrays:

let array = [{BenefitType:'401k',
   Beneficiaries: [{Name: 'PersonA', Percentage: 20},
                   {Name: 'PersonB', Percentage: 30},
                   {Name: 'PersonC', Percentage: 50}]
},
 {BenefitType:'IRA',
   Beneficiaries: [{Name: 'PersonA', Percentage: 15},
                   {Name: 'PersonB', Percentage: 45},
                   {Name: 'PersonC', Percentage: 40}]
}];


array.forEach(x => x.TotalPercentage = x.Beneficiaries.reduce((val, cur) => val + cur.Percentage, 0));

console.log(array);

EDIT:

To fix your code with double for loop you should set your myTotal variable to zero when you leave inner loop:

for(var i = 0; i < data.benefit_type.length; i++) {
    for(var j=0; j < data.benefit_type[i].Beneficiaries.length; j++) {
        myTotal += data.benefit_type[i].Beneficiaries[j].Percentage; 
        data.benefit_type[i].percent_total = myTotal;
    }
    myTotal = 0;
}

edited Jun 8, 2018 at 21:14

answered Jun 8, 2018 at 20:46

mickl

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2 Comments

Cory Kleiser Over a year ago

Why must you use map and reduce? Why not just reduce?

mickl Over a year ago

@CoryKleiser you're right, I've modified and simplified my answer based on what OP is trying to achieve

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