javascript: how to remove duplicate arrays inside array of arrays

Question

Input:

[[-1,-1,2],[-1,0,1],[-1,-1,2],[-1,0,1],[-1,-1,2],[-1,0,1],[-1,0,1]]

The output I want:

[[-1,-1,2],[-1,0,1]]

Any other ideas except this one?

Thanks

Answer 1

You won't really get around stringifying the arrays, as that's the simplest (and reasonably fast) way to compare them by value. So I'd go for

Array.from(new Set(input.map(JSON.stringify)), JSON.parse)

See also Remove Duplicates from JavaScript Array for other approaches, though most of them will require two values to be comparable by ===.

Answer 2

Magic

d.filter(( t={}, a=> !(t[a]=a in t) ));

I assume your input data are in array d. Explanation here.

let d = [[-1,-1,2],[-1,0,1],[-1,-1,2],[-1,0,1],[-1,-1,2],[-1,0,1],[-1,0,1]];

var r = d.filter((t={},a=>!(t[a]=a in t)));

console.log(JSON.stringify(r));

Answer 3

There's already a good utility for that, try Lodash, one of the function of it is _.uniqWith, with that function you can do the following.

<script src="/path/to/lodash.js"></script>
<script>
    var aa = [[-1,-1,2],[-1,0,1],[-1,-1,2],[-1,0,1],[-1,-1,2],[-1,0,1],[-1,0,1]];
    console.log(aa);
    console.log(_.uniqWith(aa,_.isEqual));
</script>

Answer 4

You can create a hashMap and save values in it. This will always hold last value.

var data = [[-1,-1,2],[-1,0,1],[-1,-1,2],[-1,0,1],[-1,-1,2],[-1,0,1],[-1,0,1]]

var hashMap = {}

data.forEach(function(arr){
  // If your subArrays can be in any order, you can use .sort to have consistant order
  hashMap[arr.join("|")] = arr;
});

var result = Object.keys(hashMap).map(function(k){
  return hashMap[k]
})

console.log(result)

Answer 5

jsfiddle

Borrowing the array comparison code from this post

// Warn if overriding existing method
if(Array.prototype.equals)
    console.warn("Overriding existing Array.prototype.equals. Possible causes: New API defines the method, there's a framework conflict or you've got double inclusions in your code.");
// attach the .equals method to Array's prototype to call it on any array
Array.prototype.equals = function (array) {
    // if the other array is a falsy value, return
    if (!array)
        return false;

    // compare lengths - can save a lot of time 
    if (this.length != array.length)
        return false;

    for (var i = 0, l=this.length; i < l; i++) {
        // Check if we have nested arrays
        if (this[i] instanceof Array && array[i] instanceof Array) {
            // recurse into the nested arrays
            if (!this[i].equals(array[i]))
                return false;       
        }           
        else if (this[i] != array[i]) { 
            // Warning - two different object instances will never be equal: {x:20} != {x:20}
            return false;   
        }           
    }       
    return true;
}

var old = [[-1,-1,2],[-1,0,1],[-1,-1,2],[-1,0,1],[-1,-1,2],[-1,0,1],[-1,0,1]], n = [];

while(old.length) {
    var arr = old.shift(), matched = false;

  for(var i = 0, len = n.length; i < len; i++) {
    if (arr.equals(n[i])) {
        matched = true;
        break;
    }
  }
  if (!matched) {
    n.push(arr);
  }
}

Answer 6

const removeDuplicates = (arr = []) => {
    const map = new Map();
    arr.forEach((x) => map.set(JSON.stringify(x), x));
    arr = [...map.values()];
    return arr;
};

console.log(
    removeDuplicates([
        [1, 1, 6],
        [1, 2, 5],
        [1, 7],
        [1, 2, 5],
        [1, 7],
        [2, 6],
    ])
);
// we can use simple JS object also to store unique elements  like { "[1, 1, 6]" : [1, 1, 6]  }
//resource - https://hackinbits.com/articles/how-to-iterate-a-map-in-javascript---map-part-2

Answer 7

If you want to prevent duplicates in array during construction:

if (!arr.includes(subArray)) {
  arr.push(subArray)
}