Calculation on array objects having same property values

Question

I have an array as-

const a = [
  {
    value: 1,
    week: 'week1',
  },
  {
    value: 2,
    week: 'week1',
  },
  {
    value: 3,
    week: 'week16',
  },
  {
    value: 4,
    week: 'week0',
  },
  {
    value: 5,
    week: 'week16',
  },
]

I want to have a modified array in the following way-

let modified = [
  {
    value: 1.5,
    week: 'week1',
  },
  {
    value: 4,
    week: 'week16',
  },
  {
    value: 4,
    week: 'week0',
  },
]

In this modified array, the duplicate week has been put only once and the value has been replaced by average of total value in the particular duplicate objects.

Answer 1

You can collect the values in an object, and then calculate the average by dividing their sum over the number of available values for a given week:

 const a = [{ value: 1, week: 'week1', }, { value: 2, week: 'week1', }, { value: 3, week: 'week16', }, { value: 4, week: 'week0', }, { value: 5, week: 'week16', }]; const result = Object.entries( a.reduce((a, {value, week}) => ({...a, [week]: [...a[week] || [], value] }), {}) ).map(([week, values]) => ({ week, value: values.reduce((a, v) => a + v, 0) / values.length })); console.log(result);

Answer 2

you can do it in simple way like below,

1.Create a map and added values of similar week and kept their count 2.Then created modified from that.

const a = [
    {
        value: 1,
        week: 'week1',
    },
    {
        value: 2,
        week: 'week1',
    },
    {
        value: 3,
        week: 'week16',
    },
    {
        value: 4,
        week: 'week0',
    },
    {
        value: 5,
        week: 'week16',
    },
];


const helperMap = {}

a.forEach((obj) => {
    if (!!helperMap[obj.week]) {
        helperMap[obj.week]['sum'] += obj.value;
        helperMap[obj.week]['count'] += 1;
    } else {
        helperMap[obj.week] = { sum: obj.value, count: 1 };
    }
});

const modified = [];
for (let week in helperMap) {
    let avgValue = helperMap[week]['sum'] / helperMap[week]['count'];
    modified.push({ week, value: avgValue });
}

console.log(modified)

We can do it in short forms using inbuilt functions also, but it will be better to understand the concept

Answer 3

 const a = [ { value: 1, week: 'week1', }, { value: 2, week: 'week1', }, { value: 3, week: 'week16', }, { value: 4, week: 'week0', }, { value: 5, week: 'week16', }, ] let modified = []; a.forEach(item => { let match = modified.find(m => m.week === item.week); if (match) match.value = (match.value + item.value); else modified.push(item); }); modified.forEach(m => m.value = m.value / a.filter(a => a.week === m.week).length); console.log(modified)