Compare objects in two arrays and return based on match in javascript

Question

I am using React for this, but the concept is in javascript. So hopefully I can leave React code out for simplicity sake.

I have two arrays that I need to filter out. My

Answer 1

You can use vanilla js for this one. When you do this loop, check out the comparisons you are making:

Iterations (omitting ID): ArrayOne vs ArrayTwo

1. 1 compares with 3
2. 2 compares with 4
3. 3 compares with undefined (will error since it's asking for undefined.id)
4. 4 compares with undefined (will error since it's asking for undefined.id)

If your elements are always going to be in order, you can loop over the first array and build out a binary search to quickly find elements in the second. This brings your time complexity to o(n * log(n)) and will be better in the long run. If you're just looking to hit MVP, you can do this:

const myFilter = (arrayOne, arrayTwo) => {
  return arrayOne.map((objectOne) => {

    // Using findIndex over includes to be able to pass callback
    // to compare the IDs
    // returns -1 if not found

    const matchIndex = arrayTwo.findIndex((objectTwo) => {
      return objectOne.id === objectTwo.id
    })


    if (matchIndex >= 0) {
      return 
 Match 
    } else {
      return 
 NoMatch 
    }

  })
}

Your time complexity will be o(n^2) in this approach, but that may be the best case depending on your circumstances. You can also use a temporary data structure, such as a Set to get o(n) time with the tradeoff of o(n) space.