JavaScript loop through two arrays and get single array

Question

I have two arrays:

var arr = [ 
  { id: 2, username: 'bill'}, 
  { id: 3, username: 'ted' }];

var b = ["ted", "bill", "john"];

how can I get one array like this:

var finalArr = [{id: 2, username: 'bill'},{id:3, username: 'ted'}. {id:0, username: 'john'}]

If user from array b exist in arr array to add id and if not id to be 0.

I tried something like this, but not working

var arr = [{
    id: 2,
    username: 'bill'
  },
  {
    id: 3,
    username: 'ted'
  }
];

var b = ["ted", "bill", "john"];

var finalArr = [];

function userExists(username) {
  var a = arr.some(item => {
    if (item.username === username) {
      finalArr.push({
        username,
        id: item.id
      })
    } else {
      finalArr.push({
        username,
        id: 0
      })
    }
  })
}

b.forEach(el => {
  userExists(el)
})

console.log(finalArr)

Does Id is a generic property ? that means, could be a chance that in the future there could be more names under b array, would you like the Ids to be generic ? — Amit Baranes
– Amit Baranes, Commented May 3, 2019 at 13:00
@Xerox33 : What if you happen to have multiple entries with the same username and different id within your arr? If you're not willing to remove those duplicates, you might check out my answer below. — Yevhen Horbunkov
– Yevhen Horbunkov, Commented May 3, 2019 at 14:02

adiga · Accepted Answer · 2019-05-03 12:47:25Z

4

Loop through b using map. Check if the username exists in arr using find. If yes, return the object. Else, return a new object with id: 0

var arr = [ 
  { id: 2, username: 'bill'}, 
  { id: 3, username: 'ted' }];

var b = ["ted", "bill", "john"];

const output = b.map(username => {
  const found = arr.find(a => a.username === username);
  return found || { username, id: 0 }
})

console.log(output)

answered May 3, 2019 at 12:47

adiga

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2 Comments

Nina Scholz Over a year ago

you change the order.

adiga Over a year ago

@NinaScholz yeah. Since OP used b.forEach, I assumed that was not important

R3tep · Accepted Answer · 2019-05-03 12:49:22Z

1

You can use map and find to construct your new array like

var arr = [{
    id: 2,
    username: 'bill'
  },
  {
    id: 3,
    username: 'ted'
  }
];

var b = ["ted", "bill", "john"];


const finalArr = b.map(username => {
  const find = arr.find(o => o.username === username);
  return find ? find : { id: 0, username }
})

console.log(finalArr)

answered May 3, 2019 at 12:49

R3tep

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Comments

Programmer · Accepted Answer · 2019-05-03 12:54:48Z

0

You can do that using reduce method.

b.reduce((result, elm) => {
    const userObj = arr.find((a) => a.username === elm);
    if(userObj) {
        result.push(userObj)
    } else {
        result.push({
            id: 0,
            username: elm
        });
    }
    return result;
}, []);

Check https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/reduce for more details about reduce.

answered May 3, 2019 at 12:54

Programmer

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Comments

Manikant Gautam · Accepted Answer · 2019-05-03 12:56:33Z

0

You can craete a dummy array for storing result and , find the existing using find. If not found create dummy object and push inside array.

var arr = [ 
  { id: 2, username: 'bill'}, 
  { id: 3, username: 'ted' }];

var b = ["ted", "bill", "john"];
myArr = [];
b.forEach(function(element) {
var el=arr.find(x => x.username === element);
  if(el){
    myArr.push(el);
  }else{
    var dummy={};
    dummy.id=0;
    dummy.username=element;
    myArr.push(dummy);
  }
});
console.log(myArr);

answered May 3, 2019 at 12:56

Manikant Gautam

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Comments

Nina Scholz · Accepted Answer · 2019-05-03 13:12:38Z

0

You could take a Set and filter by looking to the set and delete visited items. At the end concat missing items.

This solution repsects the order of the given data and adds the missing object in order of the names array.

var data = [{ id: 42, username: 'foo' }, { id: 2, username: 'bill' }, { id: 3, username: 'ted' }],
    names = ["ted", "bill", "john"],
    missing = new Set(names),
    result = data
        .filter(({ username }) => missing.delete(username))
        .concat(Array.from(missing, username => ({ id: 0, username })));

console.log(result);

.as-console-wrapper { max-height: 100% !important; top: 0; }

edited May 3, 2019 at 13:12

answered May 3, 2019 at 13:05

Nina Scholz

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