How to find and remove the elem that match in two different arrays? Javascript

Question

How to find and remove an elem that match in two different arrays?

For e.g.

let arr = [
    { startTimestamp: 1602675569525, name: "Pip" },
    { startTimestamp: 1602664708822, name: "Jimmy" },
    { startTimestamp: 1234, name: "Hero" }
];

let arr2 = [
    { startTimestamp: 1602675569525, name: "Pip" },
    { startTimestamp: 1602664708822, name: "Jimmy" }, 
    { startTimestamp: 505050, name: "Kit" }

];

If the startTimestamp match then I would like to remove those elem. Output should be

[
   { startTimestamp: 1234, name: "Hero" },
   { startTimestamp: 505050, name: "Kit" }
]

I've tried this below but it only gives me [{startTimestamp: 1234, name: "Hero"}] as I am only pushing arr[i] but I also need { startTimestamp: 505050, name: "Kit" }

let newArr = []; 

for (let i = 0; i < arr.length; i++) {
    if(arr[i].startTimestamp !== arr2[i].startTimestamp) {
            newArr.push(arr[i])
     }
    
}

What have you tried so far to solve this on your own? What problems do you have with that approach? And why do you ask us for an (opinion-based) "best approach"? — Andreas, Oct 14 '20 at 13:32
@Andreas thanks for your comment. really only need a way rather than best approach. — Jereme, Oct 14 '20 at 13:50
Does this answer your question? [Finding and removing matching and corresponding values in an array](https://stackoverflow.com/questions/60082255/finding-and-removing-matching-and-corresponding-values-in-an-array) — TylerH, Oct 15 '20 at 14:50
Also dupe of https://stackoverflow.com/questions/5767325/how-can-i-remove-a-specific-item-from-an-array and https://stackoverflow.com/questions/53534721/find-and-remove-first-matching-element-in-an-array-of-javascript-objects — TylerH, Oct 15 '20 at 14:50

score 2 · Answer 1 · answered Oct 14 '20 at 13:46

2

Best would be to merge them, and then filter on doubles:

const newArr = [...arr, ...arr2].filter(
  (item, index, self) => item.findIndex(
    (prev) => prev.startTimestamp === item.startTimestamp
  ) === index
);

answered Oct 14 '20 at 13:46

Poul Kruijt

58,329
11
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120

score 1 · Accepted Answer · answered Oct 14 '20 at 13:52

1

It will be good to merge two arrays and filter the items by removing the duplicated startTimestamp objects.

let arr = [
    { startTimestamp: 1602675569525, name: "Pip" },
    { startTimestamp: 1602664708822, name: "Jimmy" },
    { startTimestamp: 1234, name: "Hero" }
];

let arr2 = [
    { startTimestamp: 1602675569525, name: "Pip" },
    { startTimestamp: 1602664708822, name: "Jimmy" }, 
    { startTimestamp: 505050, name: "Kit" }
];

const result = [ ...arr, ...arr2 ].filter((item, index, origin) => origin.filter((subItem) => subItem.startTimestamp === item.startTimestamp).length === 1);
console.log(result);

answered Oct 14 '20 at 13:52

Derek Wang

9,675
4
14
36

thanks for your comment that worked. If you have time could you please help me with another use case? If there are duplicates I want to keep only one of it. so referencing to the same array data above. output would be ``` [ { startTimestamp: 1602675569525, name: "Pip" }, { startTimestamp: 1602664708822, name: "Jimmy" }, { startTimestamp: 1234, name: "Hero" }, { startTimestamp: 505050, name: "Kit" } ] ``` Thanks – Jereme Oct 14 '20 at 14:33
There is no duplicates on each array? So arr1 has no duplicated `startTimestamp` itself and same as `arr2`? – Derek Wang Oct 14 '20 at 14:37
1

Anyway, you can do like this. `const val = [ ...arr, ...arr2 ].reduce((acc, cur) => { if (!acc[cur.startTimestamp]) { acc[cur.startTimestamp] = cur.name; } return acc; }, {}); console.log(Object.entries(val).map(([ startTimestamp, value ]) => ({ startTimestamp, ...value })));` – Derek Wang Oct 14 '20 at 14:42
say after we merge arr1 and arr2. At this point we'll have duplicates this happens in my app. Then, I want to just keep one of the duplicates and also keep the non duplicate value. – Jereme Oct 14 '20 at 14:44
Above will answer your second question. – Derek Wang Oct 14 '20 at 14:52

How to find and remove the elem that match in two different arrays? Javascript

2 Answers2