Example 1: count duplicates array js
uniqueCount = ["a","b","c","d","d","e","a","b","c","f","g","h","h","h","e","a"];
var count = {};
uniqueCount.forEach(function(i) { count[i] = (count[i]||0) + 1;});
console.log(count);
Example 2: javascript find duplicate in array
// JavaScript - finds if there is duplicate in an array.
// Returns True or False.
const isThereADuplicate = function(arrayOfNumbers) {
// Create an empty associative array or hash.
// This is preferred,
let counts = {};
// // but this also works. Comment in below and comment out above if you want to try.
// let counts = [];
for(var i = 0; i <= arrayOfNumbers.length; i++) {
// As the arrayOfNumbers is being iterated through,
// the counts hash is being populated.
// Each value in the array becomes a key in the hash.
// The value assignment of 1, is there to complete the hash structure.
// Once the key exists, meaning there is a duplicate, return true.
// If there are no duplicates, the if block completes and returns false.
if(counts[arrayOfNumbers[i]] === undefined) {
counts[arrayOfNumbers[i]] = 1;
} else {
return true;
}
}
return false;
}
Example 3: javascript get duplicates in array
function getDuplicateArrayElements(arr){
var sorted_arr = arr.slice().sort();
var results = [];
for (var i = 0; i < sorted_arr.length - 1; i++) {
if (sorted_arr[i + 1] === sorted_arr[i]) {
results.push(sorted_arr[i]);
}
}
return results;
}
var colors = ["red","orange","blue","green","red","blue"];
var duplicateColors= getDuplicateArrayElements(colors);//["blue", "red"]
Example 4: duplicate numbers in an array javascript
[1, 1, 2, 2, 3].filter((element, index, array) => array.indexOf(element) !== index) // [1, 2]