Merge duplicates in array of objects while adding up specific field

April 21, 2022

I have an array of objects as follow :

const array = [
    {poleId: 1, jobCount: 1},
    {poleId: 1, jobCount: 2},
    {poleId: 5, jobCount: 8},
    {poleId: 7, jobCount: 1},
    {poleId: 2, jobCount: 10},
    {poleId: 2, jobCount: 3},
]

I’d like to "merge" the duplicate objects having the same poleId while adding up their jobCount, to get a result of this sort :

const result = [
    {poleId: 1, jobCount: 3},
    {poleId: 5, jobCount: 8},
    {poleId: 7, jobCount: 1},
    {poleId: 2, jobCount: 13},
]

I can’t figure out any clean way to do this.

Thanks in advance!

>Solution :

Try some thing like below. Build an object with keys as poleId and value as jobCount (combine jobCount when key is same)

const process = (arr, output = {}) => {
  arr.forEach(({ poleId, jobCount }) => {
    output[poleId] = {
      poleId,
      jobCount: (poleId in output ? output[poleId].jobCount : 0) + jobCount,
    };
  });
  return Object.values(output);
};

const array = [
  { poleId: 1, jobCount: 1 },
  { poleId: 1, jobCount: 2 },
  { poleId: 5, jobCount: 8 },
  { poleId: 7, jobCount: 1 },
  { poleId: 2, jobCount: 10 },
  { poleId: 2, jobCount: 3 },
];

console.log(process(array));