I hope my question is not asked too much in SO.
I have an array of 3 objects such as: :
const objStart1 = {
'user': 1,
'score': 15,
'date': 'Monday'
}
const objStart2 = {
'user': 1,
'score': 7,
'date': 'Friday'
}
const objStart3 = {
'user': 2,
'score': 5,
'date': 'Monday'
}
I would like to group by date then calcul the average of the score by day (and delete user) and return a new array of objects like :
const objStart1 = {
'average': 10,
'date': 'Monday'
}
const objStart2 = {
'average': 7,
'date': 'Friday'
}
It seems, we can use filter + reduce but my results are pathetic... Is there a good solution?
thank you in advance.
This should do the trick.
I put your items into an actual array, and I replaced Date with date.
const input = [
{
'user': 1,
'score': 15,
'date': 'Monday'
},
{
'user': 1,
'score': 7,
'date': 'Friday'
},
{
'user': 2,
'score': 5,
'date': 'Monday'
},
]
const sumList = input.reduce((acc, current) => {
if(!acc.find(obj => obj.date === current.date)) acc.push({date: current.date, sum: 0, count: 0})
const currCounter = acc.find(obj => obj.date === current.date)
currCounter.sum += current.score
currCounter.count++
return acc
}, [])
.map(({date, sum, count}) => ({ date, average: sum/count }))
console.log(sumList)Another way of writing it.
const arr=[ { 'user': 1, 'score': 15, 'date': 'Monday' }, { 'user': 1, 'score': 7, 'date': 'Friday' }, { 'user': 2, 'score': 5, 'date': 'Monday' } ]
const result = arr.reduce((acc, curr, i)=>{
if(!acc.find((el)=>el.date==curr.date)){
acc.push({date: curr.date, score: curr.score, count: 1})
return acc
}
acc.map(el=>el.date===curr.date?(el.score+=curr.score,el.count+=1,el):el)
return acc
},[])
console.log(result.map((el)=>({average: el.score/el.count, date: el.date})))const objStart1 = {
'user': 1,
'score': 15,
'date': 'Monday'
}
const objStart2 = {
'user': 1,
'score': 7,
'date': 'Friday'
}
const objStart3 = {
'user': 2,
'score': 5,
'date': 'Monday'
}
const objs = [objStart1, objStart2, objStart3];
let avgForDate = {};
avgForDate = objs.reduce((res, current) => {
const oldInfo = res[current.date] ?? {
count: 0,
scoreSum: 0,
};
const newInfo = {
count: oldInfo.count + 1,
scoreSum: oldInfo.scoreSum + current.score,
};
res[current.date] = newInfo;
return res;
}, avgForDate);
for(const info in avgForDate) {
console.log({
date: info,
avg: avgForDate[info].scoreSum / avgForDate[info].count,
});
}