Hashes and Symbols

Question 1

what are hashes?

Answer 1

hashes are collections of key-value pairs

Question 2

What happens when you try to access a key that doesn’t exist?

Answer 2

You will get the value nil

Question 3

What does nil mean?

Answer 3

nil is Ruby’s way of saying “nothing at all.”

Question 4

How do you set a new default value in a hash?

Answer 4

my_hash = Hash.new(“Trady Blix”)

Now if you try to access a nonexistent key in my_hash, you’ll get “Trady Blix” as a result.

Question 5

What are symbols?

Answer 5

Symbols are not strings and can only be used once. They are used for referencing method names and as hash keys.

Question 6

How do you write a symbol?

Answer 6

You write it:

:symbol_name

Question 7

Why are symbols good as hash keys?

Answer 7

1. They cant be changed once they are created (immutable)
2. Only one symbol with the same name can exist so they save memory
3. Symbols are faster.

Question 8

How do you convert between strings and symbols?

Answer 8

with
.to_s (symbol to string)
.to_sym (string to symbol)
.intern (string to symbol)

Question 9

How do you assign symbols as keys to a value?

Answer 9

You use the new syntax instead of the old hash syntax

new_hash = { 
  one: 1,
  two: 2,
  three: 3
}

Question 10

How can we filter values from a hash?

Answer 10

We use the .select method

Question 11

How do we iterate over just a value?

Answer 11

With the .each_value method

Question 12

How to we iterate over just a key?

Answer 12

With the .each_key method