How to get Ruby to retrieve specific data from a YAML file? - ruby

Question

First off, I am still a novice Ruby user so this is probably a trivial question but I'm still struggling regardless.
So I have a YAML file set up like so:
userA:
{
nick: cat ,
fruit: apple ,
canDance: true ,
age: 20
}
userB:
{
nick: dog ,
fruit: orange ,
canDance: false ,
age: 23
}
Assuming that the YAML file has been loaded into Ruby, how would I be able to retrieve specific parts of this file, such as retrieving userA's fruit, or userB's canDance? Thanks in advance.

Answer 1

You can read the required information from your YAML like this:
require 'yaml'
people = YAML.load_file('the_filename.yaml')
puts people['userA']['fruit'] #=> 'apple'
puts people['userB']['canDance'] #=> true
Note: Your YAML file seems to be valid and can be read by the default Ruby YAML parser. But it uses a very special and uncommon syntax. I suggest writing your YAML like this:
userA:
nick: cat
fruit: apple
canDance: true
age: 20
userB:
nick: dog
fruit: orange
canDance: false
age: 23

Answer 2

Updated: Your sample data can be parsed as is by Ruby's standard lib YAML, however the curly braces and commas are not required.
Here is an example with some mixed types added for hobbies
test.yml
---
userA:
nick: cat
fruit: apple
canDance: true
age: 20
hobbies:
- coding
- tennis
music:
production: true
djing: true
guitar: true
userB:
nick: dog
fruit: orange
canDance: false
age: 23
hobbies:
- coding
- ruby
sports:
tennis: always
soccer: sometimes
running: rarely
Use Ruby's Yaml core lib which you can simply require.
require 'yaml'
people = File.load_file 'test.yml'
people is now an instance of Hash class which allows you to get the values of keys by calling them inside of square braces like so:
people['userA']
Now you can dig through the object by chaining keys like this:
people['userA']['hobbies']
However note that you will get an error if the chain "breaks"
people['userB']['sports']['tennis'] # this works
=>"always"
people['userA']['sports']['tennis'] # this will raise
=>NoMethodError: undefined method `[]' for nil:NilClass
Exception is raised because people['userA']['sports'] returns nil so trying to chain ['tennis'] throws the error. A useful way to avoid this when digging through a deeply nested hash is to use .dig
people.dig('userB','sports','tennis')
=>"always"
people.dig('userA','sports','tennis')
=>nil #
people.dig('userA','music','djing')
=>true
people.dig('userB','music','djing')
=>nil
With hashes who's key's are strings you can also string interpolate. Let's say we want to randomly select a user and dig through it we may do something like:
people.dig("user#{ ['A','B'].sample }",'music','djing')