Removing duplicates from Multidimensional array of objects

Question

The problem is a simple one. I have an array of array of objects. Example:

[[{'name':'cat"}, {'name':'lion'}], [{'name':'elephant"},
{'name':'lion'}, {'name':'dog'}], [{'name':'tiger"}, {'name':'mouse'},
{'name':'dog'}]]

I want to remove duplicates using JS and retain only their first occurrences and remove their duplicates resulting in:

[[{'name':'cat"}, {'name':'lion'}], [{'name':'elephant"},
{'name':'dog'}], [{'name':'tiger"}, {'name':'mouse'}]]

How do I do this using loadash/ underscore? I have tried a bunch of options, first one involved passing an iteratee to the .uniq function, but it didn't work the way I wanted since these are 2d array. The other brute force method included iterating through all the arrays one by one and then doing a search to see if any of the other arrays contain the element and removing the element. Repeat this procedure until the last-1 of the sub-arrays.

Is don't like the brute force method, so wondering if there are any other methods I can retain unique elements.

Note that this is a 2D array of objects and all the posts on stack overflow answer 1D array of objects. I'm not looking to find duplicates in an array. I'm trying to find duplicates across all arrays in an array.

Mark · Accepted Answer · 2018-08-16 03:08:02Z

3

I nice way to deal with this is with a Set, just add your labels to the set as you filter() inside a map():

let arr = [
    [{'name':'cat'}, {'name':'lion'}], 
    [{'name':'elephant'},{'name':'lion'}, {'name':'dog'}],
    [{'name':'tiger'}, {'name':'mouse'}, {'name':'dog'}]
    ]

let known = new Set()
let filtered = arr.map(subarray => 
    subarray.filter(item => !known.has(item.name) && known.add(item.name))
)
console.log(filtered)

EDIT: If you can't use a Set, you can get the same function from a regular object:

let arr = [
    [{'name':'cat'}, {'name':'lion'}], 
    [{'name':'elephant'},{'name':'lion'}, {'name':'dog'}],
    [{'name':'tiger'}, {'name':'mouse'}, {'name':'dog'}]
    ]

let known = {}
let filtered = arr.map(subarray => 
    subarray.filter(item => !known.hasOwnProperty(item.name) && (known[item.name] = true))
)
console.log(filtered)

edited Aug 16, 2018 at 3:08

answered Aug 16, 2018 at 3:06

Mark

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2 Comments

abhididdigi Over a year ago

Cannot use a set because the platform I work with doesn't come with ES6, I'm limited to using ES5. How do we do this in ES5?

Mark Over a year ago

An object works about the same @abhididdigi, see edit.

E_net4 · Accepted Answer · 2021-07-12 12:34:47Z

2

let intervals = [
    [1, 20],
    [1, 20],
    [1, 20]
]
intervals = [...new Set(intervals.map(e => JSON.stringify(e)))].map(e => JSON.parse(e)) // [[1,20]]

edited Jul 12, 2021 at 12:34

E_net4

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answered Jul 12, 2021 at 10:57

sadat-saim

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1 Comment

I_love_vegetables Over a year ago

consider adding more explanation to the answer to help us understand more instead of just posting a block of code

Sandro Rosa · Accepted Answer · 2019-11-11 19:35:00Z

0

var a = [];
a.push( [1,2,3], [4,5,6], [1,2,3], [4,5,6] );
a.forEach( ( chunk, idx ) => { a[idx] = JSON.stringify(chunk); } );
a = [ ...new Set(a) ];
a.forEach( ( chunk, idx ) => { a[idx] = JSON.parse(chunk); } );

answered Nov 11, 2019 at 19:35

Sandro Rosa

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