Syntax error Count unique elements in array without sorting JavaScript

Count unique elements in array without sorting JavaScript

Let’s say, we have an array of literals that contains some duplicate values −

const arr = ['Cat', 'Dog', 'Cat', 'Elephant', 'Dog', 'Grapes', 'Dog', 'Lion', 'Grapes', 'Lion'];

We are required to write a function that returns the count of unique elements in the array. Will use Array.prototype.reduce() and Array.prototype.lastIndexOf() to do this −

Example

const arr = ['Cat', 'Dog', 'Cat', 'Elephant', 'Dog', 'Grapes', 'Dog',
'Lion', 'Grapes', 'Lion'];
const countUnique = arr => {
   return arr.reduce((acc, val, ind, array) => {
      if(array.lastIndexOf(val) === ind){
         return ++acc;
      };
      return acc;
   }, 0);
};
console.log(countUnique(arr));

Output

The output in the console will be −

5
Updated on: 2020-08-26T11:38:09+05:30

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