4.0 Introduction to Ruby Hashes
Creating a Hash
A Hash is a collection of key-value pairs. You retrieve or create a new
entry in a Hash by referring to its key. Hashes are also called
'associative arrays', 'dictionary', 'HashMap' etc. in other languages
A blank hash can be declared using two curly braces {}. Here is
an example of a Hash in Ruby:
student_ages = {
"Jack" => 10,
"Jill" => 12,
"Bob" => 14
}
The names (Jack, Jill, Bob) are the 'keys', and 10, 12 and 14 are the corresponding values.
Now try creating a simple hash with the following keys and values:
Ramen = 3
Dal Makhani = 4
Tea = 2
Fetch values from a Hash
You can retrieve values from a Hash object using [] operator.
The key of the required value should be enclosed within these square brackets.
Now try finding the price of a Ramen from the restaurant_menu hash:
write the name of the object, follow it with a square bracket, and place the
key inside the brackets. In this case the key is a string so enclose the key
in quotes.
That was very simple, wasn't it? One small step at a time!
Modifying a Hash
Once you've created a Hash object, you would want to add new key-value
pairs as well as modify existing values.
Here is how you would set the price of a "Ramen" in the
restaurant_menu hash:
restaurant_menu["Ramen"] = 3
In fact, you can create a blank hash and add all the values later. Now why
don't you try assigning the following values to an empty hash?
Dal Makhani: 4.5
Tea: 2
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