I am trying to get duplicate objects within an array of objects. Let's say the object is like below.
values = [ { id: 10, name: 'someName1' }, { id: 10, name: 'someName2' }, { id: 11, name: 'someName3' }, { id: 12, name: 'someName4' } ]; Duplicate objects should return like below:
duplicate = [ { id: 10, name: 'someName1' }, { id: 10, name: 'someName2' } ]; You can use Array#reduce to make a counter lookup table based on the id key, then use Array#filter to remove any items that appeared only once in the lookup table. Time complexity is O(n).
const values = [{id: 10, name: 'someName1'}, {id: 10, name: 'someName2'}, {id: 11, name:'someName3'}, {id: 12, name: 'someName4'}]; const lookup = values.reduce((a, e) => { a[e.id] = ++a[e.id] || 0; return a; }, {}); console.log(values.filter(e => lookup[e.id]));You can simplify this if your browser supports Object.groupBy:
const values = [{id: 10, name: 'someName1'}, {id: 10, name: 'someName2'}, {id: 11, name:'someName3'}, {id: 12, name: 'someName4'}]; const lookup = Object.groupBy(values, e => e.id); console.log(values.filter(e => lookup[e.id].length > 1));a in every iteration show the same object?I need detailed analysis of your code.reduce and filter if you haven't yet. I use reduce to build an object mapping of each object's id to the count of its occurrences - 1. a is the accumulator object which is passed from one callback to the next by reduce. filter uses the truthiness of lookup[e.id] to determine if an element is unique. If the lookup entry is 0 (falsey), it was only seen once and filter omits it from the result set, else it's kept.Let's say you have:
arr = [ { id:10, name: 'someName1' }, { id:10, name: 'someName2' }, { id:11, name: 'someName3' }, { id:12, name: 'someName4' } ] So, to get unique items:
unique = arr .map(e => e['id']) .map((e, i, final) => final.indexOf(e) === i && i) .filter(obj=> arr[obj]) .map(e => arr[e]); Then, result will be
unique = [ { id:10, name: 'someName1' }, { id:11, name: 'someName3' }, { id:12, name: 'someName4' } ] And, to get duplicate ids:
duplicateIds = arr .map(e => e['id']) .map((e, i, final) => final.indexOf(e) !== i && i) .filter(obj=> arr[obj]) .map(e => arr[e]["id"]) List of IDs will be
duplicateIds = [10] Thus, to get duplicates objects:
duplicate = arr.filter(obj=> dublicateIds.includes(obj.id)); Now you have it:
duplicate = [ { id:10, name: 'someName1' }, { id:10, name: 'someName2' } ] 
indexOf inside a map makes this a O(n^2) algorithm. Using the countBy or the groupBy method above is easier to understand and works in O(n).You haven't clarified whether two objects with different ids, but the same "name" count as a duplicate. I will assume those do not count as a duplicate; in other words, only objects with the same id will count as duplicate.
let ids = {}; let dups = []; values.forEach((val)=> { if (ids[val.id]) { // we have already found this same id dups.push(val) } else { ids[val.id] = true; } }) return dups; With lodash you can solve this with filter and countBy for complexity of O(n):
const data = [{ id: 10,name: 'someName1' }, { id: 10,name: 'someName2' }, { id: 11,name: 'someName3' }, { id: 12,name: 'someName4' } ] const counts = _.countBy(data, 'id') console.log(_.filter(data, x => counts[x.id] > 1))<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.10/lodash.min.js"></script>You could do the same with ES6 like so:
const data = [{ id: 10,name: 'someName1' }, { id: 10,name: 'someName2' }, { id: 11,name: 'someName3' }, { id: 12,name: 'someName4' } ] const countBy = (d, id) => d.reduce((r,{id},i,a) => (r[id] = a.filter(x => x.id == id).length, r),{}) const counts = countBy(data, 'id') console.log(data.filter(x => [x.id] > 1))You can use an array to store unique elements and use filter on values to only return duplicates.
const unique = [] const duplicates = values.filter(o => { if(unique.find(i => i.id === o.id && i.name === o.name)) { return true } unique.push(o) return false; }) With lodash you can use _.groupBy() to group elements by their id. Than _.filter() out groups that have less than two members, and _.flatten() the results:
const values = [{id: 10, name: 'someName1'}, {id: 10, name: 'someName2'}, {id: 11, name:'someName3'}, {id: 12, name: 'someName4'}]; const result = _.flow([ arr => _.groupBy(arr, 'id'), // group elements by id g => _.filter(g, o => o.length > 1), // remove groups that have less than two members _.flatten // flatten the results to a single array ])(values); console.log(result);<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.11/lodash.min.js"></script>An alternative based in @ggorlen solution with new Map() as accumulator (for better performance) and without unary operator ++ (not advised by default in projects with ESLint).
const values = [{ id: 10, name: "someName1" }, { id: 10, name: "someName2" }, { id: 11, name: "someName3" }, { id: 12, name: "someName4" },]; const lookup = values.reduce((a, e) => { a.set(e.id, (a.get(e.id) ?? 0) + 1); return a; }, new Map()); console.log(values.filter(e => lookup.get(e.id) > 1));
Try this
function checkDuplicateInObject(propertyName, inputArray) { var seenDuplicate = false, testObject = {}; inputArray.map(function(item) { var itemPropertyName = item[propertyName]; if (itemPropertyName in testObject) { testObject[itemPropertyName].duplicate = true; item.duplicate = true; seenDuplicate = true; } else { testObject[itemPropertyName] = item; delete item.duplicate; } }); return seenDuplicate; } referred from : http://www.competa.com/blog/lets-find-duplicate-property-values-in-an-array-of-objects-in-javascript/
