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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
} { |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 }
eren_jaeger.each_value { |value| puts value }
#Survey Corps

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