I have an array of objects that looks like this:

const arr  = [
{id: 123, message: { user_id: 4, text: 'fish'}}
{id: 456, message: { user_id: 4, text: 'cow'}}
{id: 789, message: { user_id: 5, text: 'chicken'}}
{id: 010, message: { user_id: 5, text: 'turkey'}}
]

I want to return the first item in the array where the message.user_id is unique. I'm expecting a result like this:

newArr  = [
{id: 123, message: { user_id: 4, text: 'fish'}}
{id: 789, message: { user_id: 5, text: 'chicken'}}
]

I can't seem to find any solution for this. I'm dealing with dynamic data so I can't exactly hardcode the user_id and the array I'm working with contains a lot of elements so I'm trying as much as possible to avoid looping through.

Please what's the best way for me to achieve this?

CodePudding user response：

Here is another similar solution but with a bit modified syntax, I hope this will be helpful:

const arr  = [
{id: 123, message: { user_id: 4, text: 'fish'}},
{id: 456, message: { user_id: 4, text: 'cow'}},
{id: 789, message: { user_id: 5, text: 'chicken'}},
{id: 010, message: { user_id: 5, text: 'turkey'}}
];
const uniqueResult = (Object.values(arr.reduce(function(acc, item) {
  if (!acc[item.message.user_id]) {
    acc[item.message.user_id] = item;
  }
  return acc;
}, {})));
console.log(uniqueResult);

CodePudding user response：

1. Create a dictionary/object.

2. Iterate through the array and check if the id is a key in it

   2.1 If yes, skip

   2.2 If not:

   • Add the row to the output
   • Add the user_id to the dictionary.

const arr  = [
{id: 123, message: { user_id: 4, text: 'fish'}},
{id: 456, message: { user_id: 4, text: 'cow'}},
{id: 789, message: { user_id: 5, text: 'chicken'}},
{id: 010, message: { user_id: 5, text: 'turkey'}}
]

const userIDs = {}

const output = arr.reduce((acc, item) => {
  const user_id = item.message.user_id
  if (userIDs[user_id]) return acc

  acc.push(item)
  userIDs[user_id] = true;
  return acc
},[])

console.log(output)