I came across this example for creating unique arrays with es6
[ ...new Set(array) ]
Which seems to work fine until I tried it with an array of objects and it didn't return unique array.
i.e.
let item = [ ...new Set([{id:123,value:'test'},{id:123,value:'test'}]) ];
Why is that ?
you can try to do
uniqueArray = a => [...new Set(a.map(o => JSON.stringify(o)))].map(s => JSON.parse(s))
I know its ugly as hell but in most cases works apart from where you have new Date() in your object param then that on stringify be converted to ISO string.
so then do
let arr = [{id:1},{id:1},{id:2}];
uniqueArray(arr) //[{id:1},{id:2}]
a = [{b: /foo/},{b: /bar/}] will return [{b:{}}]
Why is that ?
As per documentation
The Set object lets you store unique values of any type, whether primitive values or object references.
Now reference for each of those arrays inside that Set constructor will be different so they are not considered to be a unique value by the constructor.
This will work:
let objectReference = {id:123,value:'test'}
let uniqueArray = [...new Set([objectReference, objectReference])]
>> [{id:123,value:'test'}]
What you're doing:
let objRef1 = {id:123,value:'test'} // creates a reference to a location in memory
let objRef2 = {id:123,value:'test'} // creates a new reference to a different place in memory
let uniqueArray = [...new Set([objRef1, objRef2])]
>> [{id:123,value:'test'},{id:123,value:'test'}]
If you don't use a library like lodash or radash for example. You can use Set as answered by @Vic. Just a bug detected is about objects without same keys order. For example {a: '1', b: '2'} and {b: '2', a: '1'} are not string equals. Here is a working solution with covered cases
uniq(source) {
if (!Array.isArray(source)) {
return [];
}
return [...new Set(source.map(o => {
const sortedObjectKeys = Object.keys(o).sort();
const obj = Object.assign({}, ...sortedObjectKeys.map(k => ({[k]: o[k]})) as any);
return JSON.stringify(obj);
}))]
.map(s => JSON.parse(s));
}
describe(`uniq`, () => {
it('should return unique collection values', () => {
expect(uniq([{v: 1}, {v: 2}, {v: 1}])).toEqual([{v: 1}, {v: 2}]);
});
it('should return unique collection values for unsorted properties', () => {
expect(uniq([{a: 'test', v: 1}, {v: 2}, {v: 1, a: 'test'}])).toEqual([{a: 'test', v: 1}, {v: 2}]);
});
it('should return empty array for non array source', () => {
expect(uniq({v: 1})).toEqual([]);
expect(uniq('aString')).toEqual([]);
expect(uniq(125)).toEqual([]);
expect(uniq(true)).toEqual([]);
expect(uniq([])).toEqual([]);
expect(uniq(undefined)).toEqual([]);
expect(uniq(null)).toEqual([]);
});
});
[ ... new Set([{ val: 1 }, { val: 2 }, { val: 3 }]) ]gives me an array of objects...Set, two objects are never the same, even if they contain the same values