Deleting arrays of same elements in 2 dimensional array in Javascript

Question

I am wondering how you would go about deleting arrays that contain the same elements in a 2 dimensional array.

For example:

let 2dArr = [ [1, 2, 3],
              [3, 2, 1],
              [2, 4, 5],
              [4, 5, 2],
              [4, 3, 1] ];

This array would delete the second and fourth elements, returning the 2d array:

returnedArr = [ [1, 2, 3],
                [2, 4, 5],
                [4, 3, 1] ];

How exactly could this be done, preserving the 2d array? I could only think to loop through elements, comparing elements via a sort, and deleting them as you go along, but this would result in an indexing error if an element is deleted.

DecPK · Accepted Answer · 2021-12-28 06:07:54Z

6

1) You can easily achieve the result using reduce and Set as:

let twodArr = [
  [1, 2, 3],
  [3, 2, 1],
  [2, 4, 5],
  [4, 5, 2],
  [4, 3, 1],
];

const set = new Set();

const result = twodArr.reduce((acc, curr) => {
  const key = [...curr].sort((a, b) => a - b).join();
  if (!set.has(key)) {
    set.add(key);
    acc.push(curr);
  }
  return acc;
}, []);

console.log(result);

2) You can also use filter as:

let twodArr = [
  [1, 2, 3],
  [3, 2, 1],
  [2, 4, 5],
  [4, 5, 2],
  [4, 3, 1],
];

const set = new Set();

const result = twodArr.filter((curr) => {
  const key = [...curr].sort((a, b) => a - b).join();
  return !set.has(key) ? (set.add(key), true) : false;
});

console.log(result);

edited Dec 28, 2021 at 6:07

answered Dec 28, 2021 at 5:17

DecPK

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3 Comments

charlietfl Over a year ago

Need numeric sort. Works fine here only because all are single digit

DecPK Over a year ago

@charlietfl modified the code. Thanks for pointing out the mistake...

charlietfl Over a year ago

Just an oversight, never a mistake!

p4avinash · Accepted Answer · 2021-12-28 11:54:02Z

1

const seen = []

const res = array.filter((item) => {
  let key = item.sort().join()
  if(!seen.includes(key)){
    seen.push(key)
    return item
  }
})

console.log(res)

answered Dec 28, 2021 at 11:54

p4avinash

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Comments

Code Maniac · Accepted Answer · 2021-12-28 05:21:19Z

0

You can use hash map

let arr = [ [1, 2, 3], [3, 2, 1],[2, 4, 5],[4, 5, 2],[4, 3, 1] ];
let obj = {}
let final = []

for(let i=0; i<arr.length; i++){
  // create a key
  let sorted = [...arr[i]].sort((a,b)=> a- b).join`,`
  // check if this is not present in our hash map
  // add value to final out and update hash map accordingly
  if(!obj[sorted]){
    obj[sorted] = true
    final.push(arr[i])
  }
}

console.log(final)

answered Dec 28, 2021 at 5:21

Code Maniac

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Comments

charlietfl · Accepted Answer · 2021-12-28 05:36:43Z

0

Using Array.prototype.filter() and a Set as thisArg

let arr = [ [1, 2, 3],
              [3, 2, 1],
              [2, 4, 5],
              [4, 5, 2],
              [4, 3, 1] ];


let res = arr.filter(function(e){
    const sorted = [...e].sort((a,b) => a-b).join('|');
    return this.has(sorted) ? false : this.add(sorted)    
},new Set)

console.log(res)

answered Dec 28, 2021 at 5:36

charlietfl

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