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: how to get duplicate values from array in javascript
var array = [1, 2, 2, 3, 3, 4, 5, 6, 2, 3, 7, 8, 5, 22, 1, 2, 511, 12, 50, 22];
console.log([...new Set(
array.filter((value, index, self) => self.indexOf(value) !== index))]
);
Example 3: 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 4: 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 5: check for duplicates in array javascript
[1, 2, 3].every((e, i, a) => a.indexOf(e) === i) // true
[1, 2, 1].every((e, i, a) => a.indexOf(e) === i) // false
Example 6: js find duplicates in array
[1, 2, 2, 4, 3, 4].filter((e, i, a) => a.indexOf(e) !== i) // [2, 4]