使用reduce获取js数组中所有对象的键的并集

Question

Assume , we have :

var all=[
    {firstname:'Ahmed', age:12},
    {firstname:'Saleh', children:5 }
    {fullname: 'Xod BOD', children: 1}
];

The expected result is ['firstname','age', 'children', 'fullname'] : the union of keys of all objects of that array:

all.map((e) => Object.keys(e) ).reduce((a,b)=>[...a,...b],[]); 

This is work fine , However, i am seeking a solution more performance using directly reduce method without map , I did the following and it is failed.

all.reduce((a,b) =>Object.assign([...Object.keys(a),...Object.keys(b)]),[])

Answer 1

You can use Set , reduce() and Object.keys() there is no need for map.

 var all=[ {firstname:'Ahmed', age:12}, {firstname:'Saleh', children:5 }, {fullname: 'Xod BOD', children: 1} ]; var result = [...new Set(all.reduce((r, e) => [...r, ...Object.keys(e)], []))]; console.log(result) 

Answer 2

Here's a solution using generic procedures concat , flatMap , and the ES6 Set .

It's similar to @NenadVracar's solution but uses higher-order functions instead of a complex, do-it-all-in-one-line implementation. This reduces complexity in your transformation and makes it easier to re-use procedures in other areas of your program.

Not that ... spread syntax is bad, but you'll also notice this solution does not necessitate it.

 var all = [ {firstname:'Ahmed', age:12}, {firstname:'Saleh', children:5 }, {fullname: 'Xod BOD', children: 1} ]; const concat = (x,y) => x.concat(y); const flatMap = f => xs => xs.map(f).reduce(concat, []); const unionKeys = xs => Array.from(new Set(flatMap (Object.keys) (xs))); console.log(unionKeys(all)); // [ 'firstname', 'age', 'children', 'fullname' ] 

Answer 3

Try this code:

var union = new Set(getKeys(all));

console.log(union);
// if you need it to be array
console.log(Array.from(union));

//returns the keys of the objects inside the collection
function getKeys(collection) {
    return collection.reduce(
        function(union, current) {
            if(!(union instanceof Array)) {
                union = Object.keys(union);
            }
            return union.concat(Object.keys(current));
        });
}

Answer 4

Just out of curiosity, I've been benchmarking some solutions to your problem using different approaches (reduce vs foreach vs set). Looks like Set behaves well for small arrays but it's extremely slow for bigger arrays (being the best solution the foreach one).

Hope it helps.

 var all = [{ firstname: 'Ahmed', age: 12 }, { firstname: 'Saleh', children: 5 }, { fullname: 'Xod BOD', children: 1 }], result, res = {}; const concat = (x,y) => x.concat(y); const flatMap = f => xs => xs.map(f).reduce(concat, []); const unionKeys = xs => Array.from(new Set(flatMap (Object.keys) (xs))); for(var i = 0; i < 10; i++) all = all.concat(all); console.time("Reduce"); result = Object.keys(all.reduce((memo, obj) => Object.assign(memo, obj), {})); console.timeEnd("Reduce"); console.time("foreach"); all.forEach(obj => Object.assign(res, obj)); result = Object.keys(res); console.timeEnd("foreach"); console.time("Set"); result = [...new Set(all.reduce((r, e) => r.concat(Object.keys(e)), []))]; console.timeEnd("Set"); console.time("Set2"); result = unionKeys(all); console.timeEnd("Set2");