filter array of objects by another array of objects

Question

I want to filter array of objects by another array of objects.

I have 2 array of objects like this:

const array = [
    { id: 1, name: \'a1\', sub: {         


        

Answer 1

Ok, let's solve this step by step.

To simplify the process let's suppose that two elements can be considered equals if they both have the same id.

The first approach that I would use is to iterate the first array and, for each element, iterate the second one to check the conditions that you've defined above.

const A = [ /* ... */]
const B = [ /* ... */]

A.filter(el => {
  let existsInB = !!B.find(e => {
    return e.id === el.id
  }

  return existsInB && !!B.sub
})

If we are sure that the elements in A and in B are really the same when they have the same ID, we could skip all the A elements without the sub property to perform it up a little bit

A.filter(el => {
  if (!el.sub) return false

  let existsInB = !!B.find(e => {
    return e.id === el.id
  }

  return existsInB
})

Now, if our arrays are bigger than that, it means that we are wasting a lot of time looking for the element into B. Usually, in these cases, I transform the array where I look for into a map, like this

var BMap = {}
B.forEach(el => {
  BMap[el.id] = el
})

A.filter(el => {
  if (!el.sub) return false

  return !!BMap[el.id]
})

In this way you "waste" a little bit of time to create your map at the beginning, but then you can find your elements quicker.

From here there could be even more optimizations but I think this is enought for this question