Ruby Tutorial: Hashes

Hash

Ref. WGR Chapter 9, Section 9.3, Hashes

Hash

  • also known as...
    • Map
    • Associative Array
    • Dictionary
    • Name/Value Pair Store
    • Key/Value Pair Store

Hash literal

a Hash can be defined literally (inline) with braces e.g.

@@@ ruby
states = {"MA" => "Massachusetts",
          "CA" => "California"}

states["MA"] #=> "Massachusetts"

@@@ ruby
my_hash = {:a_symbol => 3, "a string" => 4}
my_hash[:a_symbol] #=> 3

my_hash[:foo] = "bar"
my_hash #=> {:a_symbol => 3, "a string" => 4, :foo => "bar"}

Hash literals

Ruby 1.8 or 1.9:

{:foo => "bar", :baz => "baf"}

Ruby 1.9 only:

{foo: "bar", baz: "baf"}

Hash access

hash[:foo] = "bar"
hash[:foo] #=> "bar"

Hash methods

  • each, each_pair
  • keys, values
  • has_key?, has_value?
  • merge, merge!
  • delete, delete_if

Hash arguments

braces are optional...

...if the hash is the final argument

(except for a default block)

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