Joining two arrays using a common property javascript

Question

What I want to do is basically join the information from two arrays via userId. Until then, this solution that I made works only when there is little data, if they are very large arrays, this huge amount of filter is very impractical. Can anyone think of a more efficient solution?

PS: I'm using > 0 ? because sometimes one of the properties is empty.

const data01 = [
      { userId: 0, motorcycles: 'motorcycle01', cars: 'car01' },
      { userId: 1, motorcycles: 'motorcycle02', cars: 'car02' },
      { userId: 2, cars: 'car03' },
      { userId: 3, motorcycles: 'motorcycle04' },
    ]


    items.forEach(
      a =>
      (
        a.motorcylces = data01.filter(b => b.userId === a.userId).length > 0 ? data01.filter(b => b.userId === a.userId)[0].motorcylces : null,
        a.cars = data01.filter(b => b.userId === a.userId).length > 0 ? data01.filter(b => b.userId === a.userId)[0].cars : null
      )
    );

    console.log(items)

Expected Output:

[
    {
       ...
       motorcycles: 'motorcycle01',
       cars: 'cars01'
    },
    {
       ...
       motorcycles: 'motorcycle01',
       cars: 'cars01'
    }
]

Can you please add a sample output? Also which one is the 2nd array ? — Dharmaraj
– Dharmaraj, Commented Jul 8, 2021 at 16:49
Why are you using the comma operator here? Just use an ordinary function body with two assignments. — Barmar
– Barmar, Commented Jul 8, 2021 at 16:50

trincot · Accepted Answer · 2021-07-08 16:59:08Z

2

You can speed up the process by creating a Map of data01, keyed by userId.

And with Object.assign you can copy the properties from a match. This will not create the property if it doesn't exist in the source, so there will be no null assignments (unless the source has an explicit null):

let map = new Map(data01.map(o => [o.userId, o]));
items.forEach(a => Object.assign(a, map.get(a.userId)));

If you are only interested in a selection of properties, then create objects that only have those properties:

let map = new Map(data01.map(o => 
    [o.userId, { cars: o.cars, motorcycles: o.motorcycles }]
));
items.forEach(a => Object.assign(a, map.get(a.userId)));

This second solution will always create the specific properties, also when they didn't exist yet. In that case their values will be undefined.

answered Jul 8, 2021 at 16:59

trincot

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3 Comments

RoktSe Over a year ago

In this case I want to keep the properties of the "items" array and add the properties "motorcycles" and "cars"

trincot Over a year ago

OK, so then go for the second variant in my answer. But also the first keeps the properties of the items array. It just doesn't always add the "motorcycles" and "cars" properties -- when they don't exist in data01.

RoktSe Over a year ago

Even with this optimization it takes more than 5 seconds to merge the data : / But your answer was good.

mik rus · Accepted Answer · 2021-07-08 17:05:46Z

If your arrays are arrays of objects, and you need to consolidate 2+ arrays based on some property in the object, seems like the best thing to do would be to make an intermediate map that has its keys as the userIDs, and then just code something that will non-destructively update the map as you iterate through the arrays.

const data01 = [
      { userId: 0, motocycles: 'motocycle01', cars: 'car01' },
      { userId: 1, motocycles: 'motocycle02', cars: 'car02' },
      { userId: 2, cars: 'car03' },
      { userId: 3, motocycles: 'motocycle04' },
    ]

const data02 = [
      { userId: 0, dogs: 'doggy', cats: 'car01' },
      { userId: 1, dogs: 'doggo', cats: 'car02' },
      { userId: 2, dogs: 'sheperd' },
      { userId: 3, cats: 'kitty' },
    ]


function combineArrFromUserId(arr1,arr2){
  const idMap= new Map()
  data01.forEach(item=>checkAndAdd(item,idMap))
  data02.forEach(item=>checkAndAdd(item,idMap))
  return idMap.values()
}

function checkAndAdd(item,map){
  const current =  map.get(item.userId)
  if(current){
    map.set(item.userId,Object.assign(current,item))
  } else {
    map.set(item.userId, item)
  }
}

console.log(combineArrFromUserId(data01,data02))

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