Transform javascript array of object to object with keys and array of values

Question

I have an array of objects I need to transform into new objects. some value as keys and an array of values.

const data = [
  {
    type: 'user',
    id: 1
  },
  {
    type: 'user',
    id: 2
  },
  {
    type: 'group',
    id: 1
  },
  {
    type: 'group',
    id: 2
  },
  {
    type: 'user',
    id: 3
  },
  {
    type: 'user',
    id: 4
  }
]

and the desired result is

const result = {
  user: [1, 2, 3, 4],
  group: [1, 2]
}

what I've tried using reduced but it not what I'm expected.

const result = data.reduce((acc, { type, ...obj }) => {
  acc[type] = data.map(item => item.id)
  return acc;
}, {})

result = { user: [ 1, 2, 1, 2, 3, 4 ], group: [ 1, 2, 1, 2, 3, 4 ] }

Answer 1

Each iterate, you check if the accumulate object has the type, if yes, push the iterated element's id to the existing array, else init the array

const data = [
  {
    type: "user",
    id: 1,
  },
  {
    type: "user",
    id: 2,
  },
  {
    type: "group",
    id: 1,
  },
  {
    type: "group",
    id: 2,
  },
  {
    type: "user",
    id: 3,
  },
  {
    type: "user",
    id: 4,
  },
]

const res = data.reduce((acc, el) => {
  if (acc[el.type]) {
    acc[el.type].push(el.id)
  } else {
    acc[el.type] = [el.id]
  }

  return acc
}, {})

console.log(res)