Run results for: Count Array Duplicates

Run details:

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:91.0) Gecko/20100101 Firefox/91.0

Browser: Firefox 91

Operating system: Mac OS X 10.15

Device Platform: Desktop

Date tested: 2 years ago

Script Preparation code:

var numbers = [...Array(1000).keys()].map(() => Math.floor(Math.random() * 100));

Tests:

Reduce + Entries + Filter
const stats = numbers.reduce((memo, val) => { if (memo[val]) { memo[val]++; } else { memo[val] = 1; } return memo; }, {}); const duplicateItems = Object.entries(stats).filter((a => a[1] > 1));
Reduce + Clone + Includes + Set
const duplicates = numbers.reduce((memo, val, index) => { const omitted = [ ...numbers ]; delete omitted[index]; if (omitted.includes(val)) { memo.push(val); } return memo; },[]); const deduped = [...new Set(...[duplicates])];
Reduce + Find + Set
const duplicates = numbers.reduce((memo, val) => { if (numbers.filter((num) => num === val).length > 1) { memo.push(val); } return memo; },[]); const deduped = [...new Set(...[duplicates])];
Reduce + Includes + Filter
numbers.reduce((memo, val) => { if (!memo.includes(val)) { if (numbers.filter((num) => num === val).length > 1) { memo.push(val); } } return memo; },[]);