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Hashes and Symbols

Ruby Symbols

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_bologna[:second_name] # => Meyer


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

Ruby Hashes, Symbols, & Values

In Ruby hashes, key symbols and their values can be defined in either of two ways, using a => or : to separate symbol keys from values.

my_progress = {
  :program => "Codecademy",
  :language => "Ruby",
  :enthusiastic? => true 
}
#Key symbols and their values can be defined with a =>, also known as a hash rocket.


my_progress = {
  program: "Codecademy",
  language: "Ruby",
  enthusiastic?: true 
}
#Key symbols and their values can also be defined with the colon (:) at the end of the symbol followed by its value.

Ruby .select Method

In Ruby, the .select method can be used to grab specific values from a hash that meet a certain criteria.

olympic_trials = {
  Sally: 9.58,
  John: 9.69,
  Bob: 14.91
}


olympic_trials.select { |name, time| time <  10.05 }
#The example above returns {:Sally=>9.58, :John=>9.69} since Sally and John are the only keys whose values meet the time < 10.05 criteria.

Ruby .each_key & .each_value

In Ruby, the .each_key and .each_value methods are used to iterate over only the keys or only the values in a hash.

eren_jaeger = {
  age: 15,
  enemy: "titans",
  branch: "Survey Corps"
}


eren_jaeger.each_key { |key| puts key }
#Output:
#age
#enemy
#branch


eren_jaeger.each_value { |value| puts value }
#Output:
#15
#titans
#Survey Corps
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