Let's say we have an array: let arr = [10,10,5,11,5]
How could I check for all the numbers that are equal? ( basically duplicates )
What i thought of is a forEach and compare every number but that's not very optimal. A filter ? Maybe. Anyone has any good ideea that would be optimal?
You can use reduce to build down the values you need
let arr = [10, 10, 5, 11, 5]; let duplicates = getDuplicates(arr); console.log(duplicates); function getDuplicates(arr) { let duplicates = arr.reduce((acc, item) => { if(acc[item] !== undefined) { acc[item] = true; } else { acc[item] = false; } return acc; }, {}); return Object.keys(duplicates).filter(item => duplicates[item]); }You can use filter
let arr = [10,10,5,11,5]; const duplicates = array => array.filter((item, index) => array.some((i, idx) => i === item && idx < index)); console.log(duplicates(arr));or reduce
let arr = [10,10,5,11,5]; const duplicates = array => array.reduce((results, item, index) => { if (!results.some(i => i === item) && array.some((i, idx) => i === item && index !== idx)) { results.push(item); } return results; }, []); console.log(duplicates(arr));You can use a Set to remove the duplicates and then compare the lengths of the two arrays.
let arr1 = [10,10,5,11,5] let arr2 = [10,11,5] function hasDuplicates(arr) { return arr.length != [...new Set(arr)].length } console.log(hasDuplicates(arr1)) console.log(hasDuplicates(arr2))Really quick with every
let arr = [10,10,5,11,5] //arr = [10,10,10,10] if (arr.every( v => v === arr[0] )) { console.log("yes") } else { console.log("no") }Or using Lodash
let arr = [10,10,5,11,5] //arr = [10,10,10,10] if (_.uniq(arr).length == 1) { console.log("yes") } else { console.log("no") }<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.11/lodash.min.js"></script>
filteralso iterates and runs a comparison. You need to be more specific with your problem statement.