How to count number of objects in an array per key?

Question

I have a JavaScript array which has the following contents:

var products = [
  {category: 'Sporting Goods', price: '$49.99', stocked: true, name: 'Football'},
  {category: 'Sporting Goods', price: '$9.99', stocked: true, name: 'Baseball'},
  {category: 'Sporting Goods', price: '$29.99', stocked: false, name: 'Basketball'},
  {category: 'Electronics', price: '$99.99', stocked: true, name: 'iPod Touch'},
  {category: 'Electronics', price: '$399.99', stocked: false, name: 'iPhone 5'},
  {category: 'Electronics', price: '$199.99', stocked: true, name: 'Nexus 7'}
];

I want to count the number of unique entries in each key.

For example,

For the key category there are 2 unique entries.
For the key name there are 5 unique entries.

I tried using Object.keys(products).length, but that only gives the total number of rows in the array.

How can I get the counts?

I can't think of any one-liner, but using just forEach should work — llamerr
– llamerr, Commented Mar 24, 2016 at 17:28

trincot · Accepted Answer · 2019-11-07 11:11:30Z

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 = new Set(products.map(p => p.category)).size;

edited Nov 7, 2019 at 11:11

trincot

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answered Mar 24, 2016 at 17:28

madox2

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Comments

trincot · Accepted Answer · 2019-11-07 11:10:38Z

0

You can achieve this by following

var map = {};

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

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

edited Nov 7, 2019 at 11:10

trincot

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answered Mar 24, 2016 at 17:29

Nikhil Aggarwal

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Comments

trincot · Accepted Answer · 2019-11-07 11:11:51Z

0

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)

edited Nov 7, 2019 at 11:11

trincot

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answered Mar 24, 2016 at 17:40

chrisrhyno2003

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