How to Reduce An Array of Objects That Contain Matching Keys/Values + Variations?

Question

What is the best way to reduce this array of objects to get the desired result?

const arr = [
  {
          "id": "561",
          "count": "1",
          "month": 7
      },
      {
          "id": "561",
          "count": "1",
          "month": 7
      },
      {
          "id": "561",
          "count": "-1",
          "month": 8
      },
      {
          "id": "561",
          "count": "1",
          "month": 9
      },
      {
          "id": "561",
          "count": "-1",
          "month": 9
      }
  ]

As you can see the id matches and some of the months match. What I would like to achieve is something along the lines of:

[
  {
    "id": "561",
    "count": 2
    "month": 7
  },
  {
    "id": "561",
    "count": -1,
    "month": 8
  },
  {
    "id": "561",
    "count": 0,
    "month": 9
  }
]

I'm basically trying to get the total count by month per id.

Shubham Khatri · Accepted Answer · 2021-03-25 11:22:04Z

2

You can use Array.prototype.reduce to group and evaluate your array based on id and month

const arr = [
  {
          "id": "561",
          "count": "1",
          "month": 7
      },
      {
          "id": "561",
          "count": "1",
          "month": 7
      },
      {
          "id": "561",
          "count": "-1",
          "month": 8
      },
      {
          "id": "561",
          "count": "1",
          "month": 9
      },
      {
          "id": "561",
          "count": "-1",
          "month": 9
      }
  ];
  
const res = Object.values(arr.reduce((acc, item) => {
   if (acc[`${item.id}-${item.month}`]) {
      acc[`${item.id}-${item.month}`] = {
        ...acc[`${item.id}-${item.month}`],
        count: `${parseInt(acc[`${item.id}-${item.month}`].count) + parseInt(item.count)}`
      }
   } else {
    acc[`${item.id}-${item.month}`] = item;
   }
   return acc;
}, {}));
console.log(res);

edited Mar 25, 2021 at 11:22

answered Mar 25, 2021 at 11:06

Shubham Khatri

284k58 gold badges431 silver badges411 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Robin Mackenzie Over a year ago

You are concatenating the count value not adding ...

Shubham Khatri Over a year ago

@RobinMackenzie I updated that part in my solution, I didn't see that count was a string in OP question

Teneff · Accepted Answer · 2021-03-25 11:28:19Z

1

Here's an example using Array.prototype.reduce to create a new array and Array.prototype.find to check if the current value is already present in the new array

const arr = [
  {
          "id": "561",
          "count": "1",
          "month": 7
      },
      {
          "id": "561",
          "count": "1",
          "month": 7
      },
      {
          "id": "561",
          "count": "-1",
          "month": 8
      },
      {
          "id": "561",
          "count": "1",
          "month": 9
      },
      {
          "id": "561",
          "count": "-1",
          "month": 9
      }
  ]

const result = arr.reduce((acc, value) => {
  const index = acc.findIndex(({id, month}) => id === value.id && month === value.month);
  if( index > -1 ) {
    acc[index]['count'] += Number(value.count);
  }
  else {
    acc.push({...value, count: Number(value.count)});
  }
  return acc;
}, [])

console.log(result)

edited Mar 25, 2021 at 11:28

answered Mar 25, 2021 at 11:07

Teneff

32.3k13 gold badges76 silver badges107 bronze badges

2 Comments

Robin Mackenzie Over a year ago

id of 561 and month 7 should have count of 2...

Teneff Over a year ago

@RobinMackenzie ah, I've missed that part in the question. thanks

Collectives™ on Stack Overflow

How to Reduce An Array of Objects That Contain Matching Keys/Values + Variations?

2 Answers 2

2 Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related