If I have an array of objects like this:
var mountains = [
{ name: 'Kebnekaise', elevation: 2106 },
{ name: 'Mount Ngauruhoe', elevation: 2291, comment: 'aka Mount Doom' }
];
How to get all unique keys i.e. ['name', 'elevation', 'comment']?
In ECMAScript 2015, it's really simple:
let mountains = [
{ name: 'Kebnekaise', elevation: 2106 },
{ name: 'Mount Ngauruhoe', elevation: 2291, comment: 'aka Mount Doom' }
];
let uniqueKeys = Object.keys(Object.assign({}, ...mountains));
Using ES6, one could do
var unique = new Set([].concat.apply([],mountains.map(Object.keys)))
Without ES6, something like
var unique = [].concat.apply([],mountains.map(Object.keys)).filter(function(value,i,arr) {
return arr.indexOf(value) === i;
});
You could iterate over the array of objects and iterate over each element's keys with Object.keys(obj), adding them to a hash to avoid duplicates:
function getKeySet (data) {
var keys = {};
data.forEach(function (datum) {
Object.keys(datum).forEach(function (key) {
keys[key] = true;
});
});
return Object.keys(keys);
}
Alternately you could add all the keys to an array and filter out duplicates. Either way this will be O(nm) where n is the number of elements in the array and m is the average number of keys.
Object.keys(result)to get the list of unique keys.