Hashes & symbols

Question 1

nil

Answer 1

returned if you try to access a hash key that does not exist.

Similar to false, but nil means nothing at all

Question 2

symbols

Answer 2

Symbols must be valid Ruby variable names and always start with a colon (:).

In Ruby, symbols are immutable names primarily used as hash keys or for referencing method names.

my_bologna = {
  :first_name => "Oscar",
  :second_name => "Meyer",
  :slices => 12
}

puts my_hash[:second_name] # => Meyer

Question 3

.to_sym

Answer 3

converts a string to a sympol

Question 4

.to_s

Answer 4

converts a symbol to a string

Question 5

.intern

Answer 5

converts a string into a symbol

Question 6

symbol syntax

Answer 6

symbol:

Question 7

.select

Answer 7

used to filter for a hash that meets a specified criteria

grades = { alice: 100,
  bob: 92,
  chris: 95,
  dave: 97
}

grades.select { |name, grade| grade <  97 }
# ==> { :bob => 92, :chris => 95 }

grades.select { |k, v| k == :alice }
# ==> { :alice => 100 }

Question 8

.each_key

Answer 8

iterates over only the keys of a hash

Question 9

.each_value

Answer 9

iterates over only the values of a hash

Question 10

when

Answer 10

acts as an If

i.e.

case choice
  when "add"
    puts "Added!"
  when "update"
    puts "Updated!"
  when "display"
    puts "Movies!"
  when "delete"
    puts "Deleted!"
  else
    puts "Error!"
end

Question 11

.to_i

Answer 11

converts a string to an integer

Question 12

.delete

Answer 12

deletes a key/value from a hash

Question 13

CRUD

Answer 13

acronym for create (add), display, update, delete.

Common actions you take when updating a database, asking a website for information, or writing a blog post.