How to count unique value from object of array in javascript

Question

I want to calculate number of unique value and put that in new array. I have below array:

[
  { CategoryId: "b5c3f43f941c", CategoryName: "Category 1", CategoryColor: "cgreen" }
  { CategoryId: "9872cce5af92", CategoryName: "Category 2", CategoryColor: "purple" }
  { CategoryId: "b5c3f43f941c", CategoryName: "Category 1", CategoryColor: "cgreen" }
]

I want new array with below result:

[
    { CategoryId: "b5c3f43f941c", count: 2, CategoryColor: "cgreen" }
    { CategoryId: "9872cce5af92", count: 1, CategoryColor: "purple" }
]

In this check by id, if id is same show count and new in new array.

Hope you understand what I want.

Thanks,

Answer 1

You can loop through array using "for..of" and create a temporary object to save data in every loop. If same id exists in tempObject then increment count by 1

var arr = [
  { CategoryId: "b5c3f43f941c", CategoryName: "Category 1", CategoryColor: "cgreen" }
  , { CategoryId: "9872cce5af92", CategoryName: "Category 2", CategoryColor: "purple" }
  , { CategoryId: "b5c3f43f941c", CategoryName: "Category 1", CategoryColor: "cgreen" }
]

var tempResult = {}

for(let { CategoryColor, CategoryId } of arr)
  tempResult[CategoryId] = { 
      CategoryId, 
      CategoryColor, 
      count: tempResult[CategoryId] ? tempResult[CategoryId].count + 1 : 1
  }      

let result = Object.values(tempResult)

console.log(result)

Answer 2

Use reduce function and inside the callback check an object exist whose CategoryId matches. If matches then update the count or else create a new object with the values and push in the array

let k = [{
    CategoryId: "b5c3f43f941c",
    CategoryName: "Category 1",
    CategoryColor: "cgreen"
  },
  {
    CategoryId: "9872cce5af92",
    CategoryName: "Category 2",
    CategoryColor: "purple"
  },
  {
    CategoryId: "b5c3f43f941c",
    CategoryName: "Category 1",
    CategoryColor: "cgreen"
  }
]

let result = k.reduce(function(acc, curr) {
  // Check if there exist an object in empty array whose CategoryId matches
  let isElemExist = acc.findIndex(function(item) {
    return item.CategoryId === curr.CategoryId;
  })
  if (isElemExist === -1) {
    let obj = {};
    obj.CategoryId = curr.CategoryId;
    obj.count = 1;
    obj.CategoryColor = curr.CategoryColor;
    acc.push(obj)
  } else {
    acc[isElemExist].count += 1
  }
  return acc;

}, [])

console.log(result)