如何计算数组和 console.log 中每个重复元素的数量？

Question

I have an array of Objects where each object has an ID property. How can I count the number of elements with the same ID property in my array?

My current logic that I've tried is to compare the ID of the current element in the loop with all the other ones and if the IDs match, I replace that element in the array with null and increment the counter by one.

The unique ID properties of each object in myArray are item_id while in the itemDB object they are id .

let field = '';
for (let i = 0; i < myArray.length; i++) {
                if (myArray[i] == null) continue;
                
                // db.items.findByPk() gets an object from the database that has the property `id`
                let itemDB = await db.items.findByPk(myArray[i].get('item_id'));
                let count = 1

    
                for (let j = i + 1; j < myArray.length; j++) {
                    if (myArray[j].get('item_id') == itemDB.get('id')) {
                        count += 1;
                        myArray[j] = null;
                    }
                }
    
                if (myArray[i].get('location') !== 'storage') weight += count * itemDB.get('weight')
                field += `${count}x - ${itemDB.get('name')}\n`
                    
            }

EDIT: I'd prefer if someone could offer me insight on a completely different approach. What I basically need is to be able to count an occurrence of each element in the array (but instead of comparing the elements directly, I'm comparing their unique ID properties since the elements are objects)

Answer 1

Well without knowing much about your code, just counting duplicates would be as easy as:

String[] strArray = ...;
int duplicateAmount = 0;
for(int i = 0; i < strArray.length(); i++) {
    for(int j = 0; j < strArray.length(); j++) {
        if(strArray[i] == strArray[j]) {
            duplicateAmount++;
        }
     }
}

If you wanted to know many different duplicates you can of course just make the duplicateAmounts an array instead where the index is equal to the index of whichever object there is a duplicate of.

Hope this helped!

(and to just be checking the ID's of something you'd of course do if(objArray[i].getId() == objArray[j].getId()) )

ALSO: I'm an idiot for writing the response in Java lol (force of habit) but hopefully it's understandable. :)

Answer 2

Lets assume you have an array of IDs

array = [{id: 'a'}, {id: 'b'}, ...]

function getRepeatedIds(array){
    return array.map((element, index) => {
        let newArray = array;
        return newArray.filter((repeatedElements, otherIndex) => element[index].id === repeatedElements[otherIndex].id ));
}) 
}

The result should be an array where in each position is an array of elements with that ID