Calculate percentages from quantities in an array of objects

I have an array containing quantities of votes by gender and would like to convert the quantities to percentages by gender.

The array is as follows:

genderResults:  [
  { Qty: 7, Gender: 'Male', Answer: 'Badminton' },
  { Qty: 8, Gender: 'Female', Answer: 'Badminton' },
  { Qty: 2, Gender: 'Male', Answer: 'None of the above' },
  { Qty: 2, Gender: 'Female', Answer: 'None of the above' },
  { Qty: 3, Gender: 'Female', Answer: 'Rugby' },
  { Qty: 5, Gender: 'Male', Answer: 'Rugby' },
  { Qty: 4, Gender: 'Male', Answer: 'Soccer' },
  { Qty: 3, Gender: 'Female', Answer: 'Soccer' },
  { Qty: 21, Gender: 'Male', Answer: 'Squash' },
  { Qty: 16, Gender: 'Female', Answer: 'Squash' },
  { Qty: 1, Gender: 'Other', Answer: 'Squash' },
  { Qty: 18, Gender: 'Female', Answer: 'Tennis' },
  { Qty: 12, Gender: 'Male', Answer: 'Tennis' }
]

The required result would be like:

genderResults:  [
  { Percentage: 47, Gender: 'Male', Answer: 'Badminton' },
  { Percentage: 53, Gender: 'Female', Answer: 'Badminton' },
  { Percentage: 50, Gender: 'Male', Answer: 'None of the above' },
  { Percentage: 50: Gender: 'Female', Answer: 'None of the above' },
  { Percentage: 37, Gender: 'Male', Answer: 'Rugby' },
  { Percentage: 63: Gender: 'Female', Answer: 'Rugby' },
  ...
]

I've tried a forEach loop and array.map but can't figure out how to group the results?

const totalQtyByGender = {};
const totalQtyByAnswer = {};

// Calculate total quantity by gender and answer
genderResults.forEach(result => {
  const { Qty, Gender, Answer } = result;
  totalQtyByGender[Gender] = (totalQtyByGender[Gender] || 0) + Qty;
  totalQtyByAnswer[Answer] = (totalQtyByAnswer[Answer] || 0) + Qty;
});

// Calculate the percentage
const output = genderResults.map(result => {
  const { Qty, Gender, Answer } = result;
  const percentage = (Qty / totalQtyByGender[Gender]) * 100;
  return { Percentage: percentage, Gender, Answer };
});

console.log(output);

We can also do it with the help of reduce method but you tried it with the help of foreach method so here it is.

It can be cleaned up a bit, but I think this will fulfill your requirements. I haven't considered any edge cases, btw.

const genderResults = [
  { Qty: 7, Gender: 'Male', Answer: 'Badminton' },
  { Qty: 8, Gender: 'Female', Answer: 'Badminton' },
  { Qty: 2, Gender: 'Male', Answer: 'None of the above' },
  { Qty: 2, Gender: 'Female', Answer: 'None of the above' },
  { Qty: 3, Gender: 'Female', Answer: 'Rugby' },
  { Qty: 5, Gender: 'Male', Answer: 'Rugby' },
  { Qty: 4, Gender: 'Male', Answer: 'Soccer' },
  { Qty: 3, Gender: 'Female', Answer: 'Soccer' },
  { Qty: 21, Gender: 'Male', Answer: 'Squash' },
  { Qty: 16, Gender: 'Female', Answer: 'Squash' },
  { Qty: 1, Gender: 'Other', Answer: 'Squash' },
  { Qty: 18, Gender: 'Female', Answer: 'Tennis' },
  { Qty: 12, Gender: 'Male', Answer: 'Tennis' }
];

const totalCount = getCount();

const genderPercent = genderResults.map(res =>{
    return {Gender: res.Gender, Answer: res.Answer, Percentage: Math.round((res.Qty / totalCount) * 100) }
});

// const maleCount = getCount('Male');
// const femaleCount = getCount('Female');

function getCount(gender){
    return genderResults.reduce((sum, item)=>{
    if(gender){
        if(item.Gender == gender){
        sum+= item.Qty;
    }
    }
    else{
         sum+= item.Qty;
    }
    return sum
},0)
}
console.log(totalCount, genderPercent)

Update:

Here you go

const categoryCount = genderResults.reduce((res, item)=>{
        if(res[item.Answer]){
            res[item.Answer]+= item.Qty
        }
        else{
            res[item.Answer] = item.Qty
        }
        return res;
}, {})

console.log({categoryCount})
const genderPercent = genderResults.map(res =>{
    return {
        Gender: res.Gender, 
        Answer: res.Answer, 
        Percentage: Math.round((res.Qty / categoryCount[res.Answer]) * 100) 
    }
});


console.log(genderPercent)

We can use Array.reduce() to group the genderResults array by
Answer.

We'll also keep track of the total quantity for each answer and use this to calculate a percentages array for each one.

Once we have this grouped value, we can use Object.values
and Array.flatMap to get the final result.

<!-- begin snippet: js hide: false console: true babel: null -->
<!-- language: lang-js -->

const genderResults =  [ { Qty: 7, Gender: 'Male', Answer: 'Badminton' }, { Qty: 8, Gender: 'Female', Answer: 'Badminton' }, { Qty: 2, Gender: 'Male', Answer: 'None of the above' }, { Qty: 2, Gender: 'Female', Answer: 'None of the above' }, { Qty: 3, Gender: 'Female', Answer: 'Rugby' }, { Qty: 5, Gender: 'Male', Answer: 'Rugby' }, { Qty: 4, Gender: 'Male', Answer: 'Soccer' }, { Qty: 3, Gender: 'Female', Answer: 'Soccer' }, { Qty: 21, Gender: 'Male', Answer: 'Squash' }, { Qty: 16, Gender: 'Female', Answer: 'Squash' }, { Qty: 1, Gender: 'Other', Answer: 'Squash' }, { Qty: 18, Gender: 'Female', Answer: 'Tennis' }, { Qty: 12, Gender: 'Male', Answer: 'Tennis' } ]
const grouped = genderResults.reduce((acc, row) => { 
const key = row.Answer;
acc[key] = acc[key] || { totalQty: 0, entries: [] };
acc[key].entries.push(row);
acc[key].totalQty += row.Qty;
acc[key].percentages = acc[key].entries.map(entry => { 
return { 
Percentage: Math.round(100 * entry.Qty / acc[key].totalQty),
Gender: entry.Gender,
Answer: entry.Answer
}
})
return acc;
}, {})
const result = Object.values(grouped).flatMap(obj => obj.percentages)
console.log('Result:')
result.forEach(r => console.log(JSON.stringify(r)))

<!-- language: lang-html -->
<!-- language: lang-css -->
.as-console-wrapper { max-height: 100% !important; }
<!-- end snippet -->

Thanks @nashit-shayan - modified your code to get what I was looking for.

const genderPercent = genderResults.map(res =>{
return {Gender: res.Gender, Answer: res.Answer, Percentage: Math.round((res.Qty / getCount(res.Answer)) * 100) }
});
function getCount(answer){
return genderResults.reduce((sum, item)=>{
if(answer){
if(item.Answer == answer){
sum+= item.Qty;
}
}
else{
sum+= item.Qty;
}
return sum
},0)
}
console.log(genderPercent)