Filter Array Not in Another Array

Question

Need to filter one array based on another array. Is there a util function in knock out ? else i need to go with javascript

First :

var obj1 = [{
    "visible": "true",
    "id": 1
}, {
    "visible": "true",
    "id": 2
}, {
    "visible": "true",
    "id": 3
}, {
    "Name": "Test3",
    "id": 4
}];

Second :

var obj2 = [ 2,3]

Now i need to filter obj1 based on obj2 and return items from obj1 that are not in obj2 omittng 2,3 in the above data (Comparison on object 1 Id)

output:

[{
    "visible": "true",
    "id": 1
}, {
    "Name": "Test3",
    "id": 4
}];

Nina Scholz · Accepted Answer · 2020-05-11 07:11:52Z

92

You can simply run through obj1 using filter and use indexOf on obj2 to see if it exists. indexOf returns -1 if the value isn't in the array, and filter includes the item when the callback returns true.

var arr = obj1.filter(function(item){
  return obj2.indexOf(item.id) === -1;
});

With newer ES syntax and APIs, it becomes simpler:

const arr = obj1.filter(i => !obj2.includes(i.id))

edited May 11, 2020 at 7:11

Nina Scholz

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answered Nov 7, 2015 at 0:55

Joseph

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Comments

vnapastiuk · Accepted Answer · 2022-03-04 09:53:19Z

3

Even if the answer provided by @Joseph are good, it can lead to performance issues if you have a very large array. The complexity is O(n^2), but it can be improved to O(n). Below I put the code I'd use to perform this task:

//create a map for storing object id
const map = new Map();
//add existing id from the array to the map
for (item of obj2) {
  map.set(item.id, true);
}

//create a new array that contains all items that aren't included in the //map
//the map lookUp is O(1) complexity
const arr = obj1.filter(item => !map[item.id]);

In this way we avoid nested iteration and have O(n) complexity

answered Mar 4, 2022 at 9:53

vnapastiuk

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1 Comment

john k Over a year ago

I think checking existence in a set is faster than retrieving the 'true' value from a map medium.com/@dm_md/….

Marwan Sulaiman · Accepted Answer · 2015-11-07 01:19:12Z

-1

To create your output array, create a function that will iterate through obj1 and populate a new array based on whether the id of every obj in the iteration exists in obj2.

var obj1 = [{
    "visible": "true",
    "id": 1
}, {
    "visible": "true",
    "id": 2
}, {
    "visible": "true",
    "id": 3
}, {
    "Name": "Test3",
    "id": 4
}];

var obj2 = [2,3]

var select = function(arr) {
  var newArr = [];
  obj1.forEach(function(obj) {
    if obj2.indexOf(obj.id) !== -1 {
      newArr.push(obj)
    };
  };
  return newArr;
};

answered Nov 7, 2015 at 1:19

Marwan Sulaiman

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