Using Lodash or vanilla JS what is the most efficient way to filter an array based on object keys?

Question

I have two arrays of objects:

array1 = [
    {id:1, name: 'one'},
    {id:4, name: 'four'}
]

array2 = [
    {id:1, name: 'one'},
    {id:2, name: 'two'},
    {id:3, name: 'three'},
    {id:5, name: 'five'},
    {id:6, name: 'six'},
    {id:7, name: 'seven'}
]

I would like to remove any object from array1 who's id does not exist in array2.

so my expect result would be:

array1 = [
    {id:1, name:'one'}
]

In other words, you want to find the intersection between two arrays? https://stackoverflow.com/questions/1885557/simplest-code-for-array-intersection-in-javascript — Derek 朕會功夫, Nov 10 '17 at 20:13
What is the definition of "efficient" as used at Question? What are the benchmarks of the code that you have tried to resolve inquiry? See https://stackoverflow.com/help/mcve — guest271314, Nov 10 '17 at 20:24

score 2 · Accepted Answer · answered Nov 10 '17 at 20:50

Use lodash's _.intersectionBy():

var array1 = [
    {id:1, name: 'one'},
    {id:4, name: 'four'}
];

array2 = [
    {id:1, name: 'one'},
    {id:2, name: 'two'},
    {id:3, name: 'three'},
    {id:5, name: 'five'},
    {id:6, name: 'six'},
    {id:7, name: 'seven'}
];

var result = _.intersectionBy(array1, array2, 'id');

console.log(result);

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.4/lodash.min.js"></script>

score 1 · Answer 2 · answered Nov 10 '17 at 20:40

1

A fast and readable option would be:

var referenceKeys = array2.map(function(entity) { return entity.id; });

var result = array1.filter(function(entity) {
    return referenceKeys.indexOf(entity.id) !== -1;
});

But no guarantee that it's the fastest in all dimensions. (Number of repeats, length of array1, length of array2).

answered Nov 10 '17 at 20:40

K. Rohde

9,439
1
31
51

1

Depending on what is meant by "efficient" this may not be a good solution since it is quadratic. – Justin Summerlin Nov 10 '17 at 20:55

score 0 · Answer 3 · answered Nov 10 '17 at 20:44

You could use a standard approach by using a hash table which uses just one iteration for both arrays.

var array1 = [{ id: 1, name: 'one' }, { id: 4, name: 'four' }],
    array2 = [{ id: 1, name: 'one' }, { id: 2, name: 'two' }, { id: 3, name: 'three' }, { id: 5, name: 'five' }, { id: 6, name: 'six' }, { id: 7, name: 'seven' }],
    hash = Object.create(null),
    result;

array2.forEach(function (o) {
    hash[o.id] = true;
});

result = array1.filter(function (o) {
    return hash[o.id];
});

console.log(result);

score 0 · Answer 4 · answered Nov 10 '17 at 20:48

0

You can use a Set for this:

const seenIds = array2.reduce((set, o) => set.add(o.id), new Set());
const result = array1.filter(o => seenIds.has(o.id));

answered Nov 10 '17 at 20:48

Justin Summerlin

4,938
1
16
10

`const seenIds = new Set(array2.map(o -> o.id));` Just a little shorter. :) – Nov 15 '17 at 19:05

Using Lodash or vanilla JS what is the most efficient way to filter an array based on object keys?

4 Answers4