I have two lists in javascript that are not same structure like below:

var required_documents = [{"id":1,"dt":1},{"id":2,"dt":2},{"id":3,"dt":3}];
var existing_documents = [{"id":1,"dt":1},{"id":2,"dt":2},{"id":3,"dt":4}];

I need to remove all records from database that are in existing documents list (i.e "dt") but NOT in required_documents list. For the above scenario I should remove only {"id":3,"dt":4} and insert {"id":3,"dt":3}. I am not sure how I can compare on just one property. This is below that I found on SOF sometime ago but can't find it again apologies for not referencing it.

required_documents.forEach((obj) => {
    const elementInArr2 = existing_documents.find((o) => o.dt === obj.dt);
    console.log('found elementinarr: '   obj.dt);
});

This returns unique objects like dt:1,dt:2,dt:3 but I need dt:4 from the existing documents list as it is the one that is not in the required documents list and needs to be deleted. How can I get just the one that is not in the required documents list.

CodePudding user response：

If you don't care about time complexity, something like

var new_documents = existing_documents.filter(el_1 => {
  return required_documents.find(el_2 => el_2.dt == el_1.dt);
});

should work.

Edit: Okay, I just reread your question and I'm a bit confused. Do you want the object {id: 3, dt: 3} inside the new array as well?

CodePudding user response：

You need to run it twice to confirm there is no elements left in existing. So create a function and use it.

var required_documents = [{"id":1,"dt":1},{"id":2,"dt":2},{"id":3,"dt":3}];
var existing_documents = [{"id":1,"dt":1},{"id":2,"dt":2},{"id":3,"dt":4}]

let output = [];
output = output.concat(extractUniqueValues(required_documents, output));
output = output.concat(extractUniqueValues(existing_documents, output));
console.log(output)
function extractUniqueValues(input, output){
  return input.filter((item)=>{
     return !output.find(v => v.dt == item.dt)
  })
}

CodePudding user response：

Assuming both id and dt properties are significant, I would first create a means of hashing an entry and then build a hashed set of required_documents.

Then you can filter out anything from existing_documents that is in the set, leaving only the results you want.

const required_documents = [{"id":1,"dt":1},{"id":2,"dt":2},{"id":3,"dt":3}];
const existing_documents = [{"id":1,"dt":1},{"id":2,"dt":2},{"id":3,"dt":4}];

// a simple stringify hash
const createHash = ({ id, dt }) => JSON.stringify({ id, dt });

const requiredHashSet = new Set(required_documents.map(createHash));

const result = existing_documents.filter(
  (doc) => !requiredHashSet.has(createHash(doc))
);

console.log(result);

The hash creation can be anything that produces a comparable entity that can uniquely identify a record.

CodePudding user response：

You can do like below

var required_documents = [
  { id: 1, dt: 1 },
  { id: 2, dt: 2 },
  { id: 3, dt: 3 },
];
var existing_documents = [
  { id: 1, dt: 1 },
  { id: 2, dt: 2 },
  { id: 3, dt: 4 },
];

for (let index = 0; index < required_documents.length; index  ) {
  const element = required_documents[index];
  for (var i = existing_documents.length - 1; i >= 0; i--) {
    const child = existing_documents[i];
    if (element.id === child.id && element.dt === child.dt) {
      existing_documents.splice(i, 1);
    } else {
      required_documents.push(element);
    }
  }
}

LOG  not exist [{"dt": 4, "id": 3}]
LOG unique items [{"dt": 1, "id": 1}, {"dt": 2, "id": 2}, {"dt": 3, "id": 3}]