Merge duplicate values in json using ruby

Question

I have the following item.json file

{
    "items": [
      {
        "brand": "LEGO",
        "stock": 55,
        "full-price": "22.99",
      },
      {
        "brand": "Nano Blocks",
        "stock": 12,
        "full-price": "49.99",
      },
      {
        "brand": "LEGO",
        "stock": 5,
        "full-price": "199.99",
      }
    ]
}

There are two items named LEGO and I want to get output for the total number of stock for the individual brand.

In ruby file item.rb i have code like:

require 'json'

path = File.join(File.dirname(__FILE__), '../data/products.json')
file = File.read(path)
products_hash = JSON.parse(file)

products_hash["items"].each do |brand|
puts "Stock no: #{brand["stock"]}"
end

I got output for stock no individually for each brand wherein I need the stock to be summed for two brand name "LEGO" displayed as one. Anyone has solution for this?

Phrogz · Accepted Answer · 2016-04-06 03:48:08Z

json = File.open(path,'r:utf-8',&:read) # in case the JSON uses UTF-8
items = JSON.parse(json)['items']
stock_by_brand = items
  .group_by{ |h| h['brand'] }
  .map do |brand,array|
    [ brand,
      array
        .map{ |item| item['stock'] }
        .inject(:+) ]
  end
  .to_h
#=> {"LEGO"=>60, "Nano Blocks"=>12}

It works like this:

Enumerable#group_by takes the array of items and creates a hash mapping the brand name to an array of all item hashes with that brand
Enumerable#map turns each brand/array pair in that hash into an array of the brand (unchanged) followed by:
- Enumerable#map on the array of items picks out just the "stock" counts, and then
- Enumerable#inject sums them all together
Array#to_h then turns that array of two-value arrays into a hash, mapping the brand to the sum of stock values.

If you want simpler code that's less functional and possibly easier to understand:

stock_by_brand = {}  # an empty hash
items.each do |item|
  stock_by_brand[ item['brand'] ] ||= 0 # initialize to zero if unset
  stock_by_brand[ item['brand'] ] += item['stock']
end
p stock_by_brand     #=> {"LEGO"=>60, "Nano Blocks"=>12}

Cary Swoveland · Accepted Answer · 2016-04-07 00:38:34Z

To see what your JSON string looks like, let's create it from your hash, which I've denoted h:

require 'json'

j = JSON.generate(h)
  #=> "{\"items\":[{\"brand\":\"LEGO\",\"stock\":55,\"full-price\":\"22.99\"},{\"brand\":\"Nano Blocks\",\"stock\":12,\"full-price\":\"49.99\"},{\"brand\":\"LEGO\",\"stock\":5,\"full-price\":\"199.99\"}]}"

After reading that from a file, into the variable j, we can now parse it to obtain the value of "items":

arr = JSON.parse(j)["items"]
  #=> [{"brand"=>"LEGO", "stock"=>55, "full-price"=>"22.99"},
  #    {"brand"=>"Nano Blocks", "stock"=>12, "full-price"=>"49.99"},
  #    {"brand"=>"LEGO", "stock"=>5, "full-price"=>"199.99"}]

One way to obtain the desired tallies is to use a counting hash:

arr.each_with_object(Hash.new(0)) {|g,h| h.update(g["brand"]=>h[g["brand"]]+g["stock"])}
  #=> {"LEGO"=>60, "Nano Blocks"=>12}

Hash.new(0) creates an empty hash (represented by the block variable h) with with a default value of zero¹. That means that h[k] returns zero if the hash does not have a key k.

For the first element of arr (represented by the block variable g) we have:

g["brand"] #=> "LEGO"
g["stock"] #=> 55

Within the block, therefore, the calculation is:

g["brand"] => h[g["brand"]]+g["stock"]
  #=> "LEGO" => h["LEGO"] + 55

Initially h has no keys, so h["LEGO"] returns the default value of zero, resulting in { "LEGO"=>55 } being merged into the hash h. As h now has a key "LEGO", h["LEGO"], will not return the default value in subsequent calculations.

Another approach is to use the form of Hash#update (aka merge!) that employs a block to determine the values of keys that are present in both hashes being merged:

arr.each_with_object({}) {|g,h| h.update(g["brand"]=>g["stock"]) {|_,o,n| o+n}}
  #=> {"LEGO"=>60, "Nano Blocks"=>12}

^{1 k=>v is shorthand for { k=>v } when it appears as a method's argument.}

Collectives™ on Stack Overflow

Merge duplicate values in json using ruby

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related