How To Count Number Of Objects In An Array Per Key?

I have a JavaScript array which has the following contents: var products = [ {category: 'Sporting Goods', price: '$49.99', stocked: true, name: 'Football'}, {category: 'Sportin

Solution 1:

You can reduce array to get unique values as keys of reduced object and then apply Object.keys(), for example:

var categoryCount = Object.keys(products.reduce(function(r, o) {
    r[o.category] = 1;
    return r;
}, {})).length;

In ECMAScript 2015 you can use Set data structure to get unique values:

const categoryCount = newSet(products.map(p => p.category)).size;

Solution 2:

You can achieve this by following

var map = {};

products.map(function(product){
    map[product.category] = undefined;        
});

console.log(Object.keys(map).length);

Solution 3:

I was able to achieve the same through a one line code. I am unsure if this is the most efficient one though:

var categoryCount = $.unique(products.map(function (d) {return (d.category);}));
alert(categoryCount.length)