How to find duplicates in an array using set() and filter() methods in JavaScript?

JavascriptObject Oriented ProgrammingFront End Technology

Removing duplicates

To remove duplicates in an array we have many logical methods, but advanced javascript has provided some methods so that the task of removing duplicates has become very simple. Some of those methods are set() and filter(). For better understanding lets' discuss each method individually.

Set()

The important use of the set() method is that it only allows unique values. In other words, it will automatically remove duplicates and makes the task easy for us. The Set() method won't take any logical approach in removing duplicates.

Example

In the following example, the duplicates in the provided array have been removed without any logical approach by using set() method. 

Live Demo

<html>
<body>
<script>
   var dupNames = ['John', 'Ram', 'Rahim', 'Remo', 'Ram', 'Rahim'];
   var uniArr = [...new Set(dupNames)];
   document.write("Before removing :" +" "+ dupNames);
   document.write("</br>");
   document.write("After using set() method :" +" "+ uniArr);
</script>
</body>
</html>

Output

Before removing : John,Ram,Rahim,Remo,Ram,Rahim
After using set() method : John,Ram,Rahim,Remo


filter()

In the following example, using filter() method each element is scrutinized whether it is repeated two or more times. If any element found repeated two or more times then only one of its value is permitted and displayed as shown in the output.

Example

Live Demo

<html>
<body>
<script>
   var dupnam = ['John', 'Ram', 'Rahim', 'Remo', 'Ram', 'Rahim'];
   var x = (dupname) => dupname.filter((v,i) => dupname.indexOf(v) === i)
   document.write("Before removing : " +" "+ dupname);  
   document.write("</br>");
   document.write("After filter() method :" +" "+x(dupname));
</script>
</body>
</html>

Output

Before removing : John,Ram,Rahim,Remo,Ram,Rahim
After filter() method : John,Ram,Rahim,Remo
raja
Published on 01-Jul-2019 13:56:48
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