Lesson content is currently in draft form.

In the last chapter we parsed a JSON file containing Twitter account information.

But what does that mean, exactly?

Run the routine again to fetch the info for a Twitter account:

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require 'rubygems'
require 'json'
require 'httparty'

url = "http://nottwitter.danwin.com/users/NancyPelosi/show.json"
json_str = HTTParty.get(url).body
twitter_user = JSON.parse(json_str)

Note: The rest of this lesson assumes that twitter_user contains the value that it does at the end of this routine. If you exit and relaunch irb, just re-run this routine to follow along again.

What is the class of the parsed JSON?

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puts twitter_user.class
#=> Hash

The Hash Object

The Hash is one of Ruby’s collection classes and is ubiquitous in Ruby coding (in Python, it’s called a dictionary).

Collection classes are data objects that are collections of other data objects (so yes, this means a Hash can contain many other Hash objects).

Here’s how a simple Hash object is initialized:

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simple_hash = {'a' => 101}

• The curly-braces denote the entire Hash.
• Hashes are composed of key-value pairs
• This simple_hash has only one item, i.e. one key-value pair
• The key in that single pair is on the left side: 'a'. The value is on the right, i.e. 101

Accessing members of a Hash

To access an item in a Hash, we use square-bracket notation to specify the key of the value that we want.

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simple_hash = {'a' => 101}
puts simple_hash['a']
# => 101

Try it yourself. In the Hash below: 1. Print out the value at key 42 2. Access the pair with the value of "dog" and store the value (i.e. "dog") in a variable

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multi_hash = {'a' => 101, 42 => 'life', 999 => '9', "Hello world" => "dog"}

puts multi_hash[42]
#=> life
v = multi_hash['Hello world']
puts v
#=> "dog"

Exercise

Go back to the twitter_user object, which we initialized at the beginning of this lesson. Print out:

1. The user’s real name
2. The user’s Twitter bio
3. The user’s number of followers

Hint: Printing out the twitter_user object might be helpful here.

Answer

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puts twitter_user['name']
#=> Nancy Pelosi

puts twitter_user['description']
#=> Democratic Leader, focused on strengthening America's middle class and creating jobs; mother, grandmother, dark chocolate connoisseur.

puts twitter_user['followers_count']
#=> 226259

Bonus: What happens when you try to access a non-existent key?