How to check if all values of a given array are unique

Question

I need to write a function in JavaScript which would return a boolean after checking if all values of a given array are unique. Examples

[1,2,3,4] true
[1,2,1,4] false, since the array has value '1' twice

Additionally `myArray.some((x, i, l) => l.indexOf(x) !== i)` is true iff `myArray` contains a duplicate. — CRice, Feb 20 '18 at 23:03
Similar to https://stackoverflow.com/questions/7376598/in-javascript-how-do-i-check-if-an-array-has-duplicate-values — A J, Feb 20 '18 at 23:11

score 2 · Accepted Answer · answered Feb 20 '18 at 23:06

2

You compare length of your array and size of the Set which always contains uniq entries.

const isUnique = (arrToTest) => 
  arrToTest.length === new Set(arrToTest).size

console.log(isUnique([1,1,2,3]));
console.log(isUnique([1,2,3]));

answered Feb 20 '18 at 23:06

Karen Grigoryan

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Of course, this won't work in all browsers (points dagger at internet exploder < 11) – Jaromanda X Feb 20 '18 at 23:49
@JaromandaX Of course if you check it in ie6 it also won't work, of course if you don't use babel or other transpilers and polyfills in your build chain in your day to day flow when using es6+, you are still likely to have problems with various old browser versions. This goes without saying, and half of the answers on stackoverflow that include es6+ answers imply that. – Karen Grigoryan Feb 21 '18 at 07:16
2

I know, I just like to remind people that internet exploder must die – Jaromanda X Feb 21 '18 at 10:51

score 0 · Answer 2 · answered Feb 20 '18 at 23:05

You can sort and check for each sibling.

var array1 = [1,2,3,4];
var array2 = [1,2,1,4];

function decorate(array) {
  array.uniques = function() {
    this.sort();
    for (var i = 0; i < this.length; i++) {
      if (this[i + 1] === this.length) return true;
      if (this[i] === this[i + 1]) return false;
    }
  }
}

decorate(array1);
decorate(array2);

console.log(array1.uniques());
console.log(array2.uniques());

score 0 · Answer 3 · answered Feb 20 '18 at 23:16

You can use a custom object

function checkUnique(array)
{ var i,obj={};
  for(i=0;i<array.length;i++)
  { if(obj[array[i]])
      return false;
    obj[array[i]]=true;
  }
  return true;
}
console.log(checkUnique([1,2,3,4]));
console.log(checkUnique([1,2,1,4]));

How to check if all values of a given array are unique

3 Answers3