Ruby Hashes

A Ruby hash is a collection of unique keys and their values. They are similar to arrays but array use integer as an index and hash use any object type. They are also called associative arrays, dictionaries or maps.

If a hash is accessed with a key that does not exist, the method will return nil.

Syntax:

name = {"key1" => "value1", "key2" => "value2", "key3" => "value3"...}  

                    OR  

name = {key1:  'value1', key2:  'value2', key3:  'value3'...}

---

Creating Ruby Hash

Ruby hash is created by writing key-value pair within {} curly braces.

To fetch a hash value, write the required key within [] square bracket.

Example:

color = {   

    "Rose" => "red",   

    "Lily" => "purple",   

    "Marigold" => "yellow",   

    "Jasmine" => "white"   

  }   

  puts color['Rose']   

  puts color['Lily']   

  puts color['Marigold']   

  puts color['Jasmine']

Output:

---

Modifying Ruby Hash

A Ruby hash can be modified by adding or removing a key value pair in an already existing hash.

Example:

color = {   

    "Rose" => "red",   

    "Lily" => "purple",   

    "Marigold" => "yellow",   

    "Jasmine" => "white"   

  }   

  color['Tulip'] = "pink"   

  color.each do |key, value|   

  puts "#{key} color is #{value}"   

 end

Output:

---

Ruby Hash Methods

A Ruby hash has many methods. Some are public class methods and some public instance methods.

Public Class Methods

Method	Description
Hash[object]	Create a new hash with given objects.
new(obj)	Return a new empty hash.
try_convert(obj)	Try to convert obj into hash.

---

Public Instance Methods

Method	Description
hsh==other_hash	Two hashes are equal if they contain same key and value pair.
hsh[key]	Retrieve value from the respective key.
hsh[key] = value	Associates new value to the given key.
assoc(obj)	Compare obj in the hash.
clear	Remove all key value pair from hash.
compare_by_identity	Compare hash keys by their identity.
compare_by_identity?	Return true if hash compare its keys by their identity.
default(key=nil)	Return default value.
default = obj	Sets the default value.
delete(key)	Delete key value pair.
each	Call block once for each key in hash.
empty?	Return true if hash contains no key value pair.
eql>(other)	Return true if hash and other both have same content
fetch(key[, default])	Return value from hash for a given key.
flatten	Return a new array that is a one-dimensional flattening of this hash.
has_key?(key)	Return true if given key is present in hash.
has_value?(value)	Return true if given value is present in hash for a key.
include?(key)	Return true if given key is present in hash.
to_s/ inspect	Return content of hash as string.