Question

How to count the duplicates in an array with Node.js

Answer 1

const arr = ['node.js', 'c', 'c', 'javascript', 'node.js', 'c++', 'c++', 'c++', 'php', 'php'];
 
const count = {};
 
arr.forEach(element => {
  count[element] = (count[element] || 0) + 1;
});
 
console.log(count);
 
let i = 0;
for (let key in count) { 
    let value = count[key];
    if (value > 1) {
            console.log(key); 
        i++;
    }
}    
 
console.log("duplicates: " + i);    
    
    
    
    
/*
run:
    
{ 'node.js': 2, c: 2, javascript: 1, 'c++': 3, php: 2 }
node.js
c
c++
php
duplicates: 4
    
*/

 

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