let arr = [1, 2, 3, 4, 5, 5];
const seen = new Set();
const duplicates = arr.filter(n => seen.size === seen.add(n).size);
console.log(duplicates); // [ 5 ]
console.log(duplicates.length); // 1// This code was pasted by ProgrammerRimon, 2022-02-18
// Find dublicates numbers from array;
const a = [1,1,1,3,3,4,5,5,6,7,8,8,8,8,8,9,2];
function findDublicatesNumbersFromArray(a) {
var d = [];
for (let i = 0; i < a.length; i++) {
var ct = a[i];
var cmt = 0;
for(var x = 0; x<a.length;++x) {
if(ct === a[x]) {
cmt++
if(cmt > 1) {
d.push(a[i])
}
}
}
}
return d.filter((i, ix)=> d.indexOf(i) === ix);
}
console.log(findDublicatesNumbersFromArray(a)) [1, 2, 3].every((e, i, a) => a.indexOf(e) === i) // true
[1, 2, 1].every((e, i, a) => a.indexOf(e) === i) // false
[1, 1, 2, 2, 3].filter((element, index, array) => array.indexOf(element) !== index) // [1, 2]const findDuplicates = (arr) => {
let sorted_arr = arr.slice().sort(); // You can define the comparing function here.
// JS by default uses a crappy string compare.
// (we use slice to clone the array so the
// original array won't be modified)
let results = [];
for (let i = 0; i < sorted_arr.length - 1; i++) {
if (sorted_arr[i + 1] == sorted_arr[i]) {
results.push(sorted_arr[i]);
}
}
return results;
}
let duplicatedArray = [9, 4, 111, 2, 3, 4, 9, 5, 7];
console.log(`The duplicates in ${duplicatedArray} are ${findDuplicates(duplicatedArray)}`);const names = ['Mike', 'Matt', 'Nancy', 'Adam', 'Jenny', 'Nancy', 'Carl']
const count = names =>
names.reduce((a, b) => ({ ...a,
[b]: (a[b] || 0) + 1
}), {}) // don't forget to initialize the accumulator
const duplicates = dict =>
Object.keys(dict).filter((a) => dict[a] > 1)
console.log(count(names)) // { Mike: 1, Matt: 1, Nancy: 2, Adam: 1, Jenny: 1, Carl: 1 }
console.log(duplicates(count(names))) // [ 'Nancy' ]