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Loop through map and push to a new object group if items have matching values

February 3, 2023

I have the following data structure in its simplest form:

items: [
   { id: 1, account: 'acct_101' },
   { id: 2, account: 'acct_52' },
   { id: 3, account: 'acct_33' },
   { id: 4, account: 'acct_101' },
   { id: 5, account: 'acct_101' },
]

I would like to separate the items into groups based on their account data. The data is dynamic; I don’t know in advance what the account numbers may be.

I can loop through the data:

items.map((item) => (
   console.log("item account: ", item.account)
))

Yet unsure how to match if an item.account already exists and if so add to an existing data object, if not create a new object group.

The desired output could like like this:

item_groups:  [
  { 
    acct_101: [
      { id: 1, account: 'acct_101' },
      { id: 4, account: 'acct_101' },
      { id: 5, account: 'acct_101' },
    ],
    acct_52: [
      { id: 2, account: 'acct_52' },
    ],
    acct_33: [
     { id: 2, account: 'acct_33' },
    ],
  }
]

>Solution :

Try like below:

const items = [
   { id: 1, account: 'acct_101' },
   { id: 2, account: 'acct_52' },
   { id: 3, account: 'acct_33' },
   { id: 4, account: 'acct_101' },
   { id: 5, account: 'acct_101' },
]

const output = items.reduce((prev, curr) => {
  if(prev[curr.account]) {
    prev[curr.account].push(curr)
  } else {
    prev[curr.account] = [curr]
  }
  return prev
}, {})

console.log([output])

More shorter form:

const items = [
   { id: 1, account: 'acct_101' },
   { id: 2, account: 'acct_52' },
   { id: 3, account: 'acct_33' },
   { id: 4, account: 'acct_101' },
   { id: 5, account: 'acct_101' },
]

const output = items.reduce((prev, curr) => {
  prev[curr.account] = (prev[curr.account] ?? []).concat(curr)
  return prev
}, {})

console.log([output])

Using Array.prototype.reduce()