constants | attributes | methods
Class

Hash

Inheritance
< Object
Included Modules
Enumerable

A Hash is a collection of key-value pairs. It is similar to an Array, except that indexing is done via arbitrary keys of any object type, not an integer index. The order in which you traverse a hash by either key or value may seem arbitrary, and will generally not be in the insertion order.

Hashes have a default value that is returned when accessing keys that do not exist in the hash. By default, that value is nil.

Hash uses key.eql? to test keys for equality. If you need to use instances of your own classes as keys in a Hash, it is recommended that you define both the eql? and hash methods. The hash method must have the property that a.eql?(b) implies a.hash == b.hash. 

  class MyClass
    attr_reader :str
    def initialize(str)
      @str = str
    end
    def eql?(o)
      o.is_a?(MyClass) && str == o.str
    end
    def hash
      @str.hash
    end
  end

  a = MyClass.new("some string")
  b = MyClass.new("some string")
  a.eql? b  #=> true

  h = {}

  h[a] = 1
  h[a]      #=> 1
  h[b]      #=> 1

  h[b] = 2
  h[a]      #=> 2
  h[b]      #=> 2

Methods

Class

Visibility Signature
public [] (...)
public new (...)

Instance

Visibility Signature
public == (p1)
public [] (p1)
public []= (p1, p2)
public clear ()
public default (...)
public default= (p1)
public default_proc ()
public delete (p1)
public delete_if ()
public each ()
public each_key ()
public each_pair ()
public each_value ()
public empty? ()
public eql? (p1)
public fetch (...)
public has_key? (p1)
public has_value? (p1)
public hash ()
public include? (p1)
public index (p1)
public indexes (...)
public indices (...)
public initialize_copy (p1)
public inspect ()
public invert ()
public key? (p1)
public keys ()
public length ()
public member? (p1)
public merge (p1)
public merge! (p1)
public pretty_print (q)
public pretty_print_cycle (q)
public rehash ()
public reject ()
public reject! ()
public replace (p1)
public select ()
public shift ()
public size ()
public sort ()
public store (p1, p2)
public to_a ()
public to_hash ()
public to_s ()
public to_yaml ( opts = {} )
public update (p1)
public value? (p1)
public values ()
public values_at (...)
public yaml_initialize ( tag, val )

Class Method Detail

Hash[ [key =>|, value]* ] => hash

Creates a new hash populated with the given objects. Equivalent to the literal { key, value, … }. Keys and values occur in pairs, so there must be an even number of arguments. 

   Hash["a", 100, "b", 200]       #=> {"a"=>100, "b"=>200}
   Hash["a" => 100, "b" => 200]   #=> {"a"=>100, "b"=>200}
   { "a" => 100, "b" => 200 }     #=> {"a"=>100, "b"=>200}

Hash.new => hash
Hash.new(obj) => aHash
Hash.new {|hash, key| block } => aHash

Returns a new, empty hash. If this hash is subsequently accessed by a key that doesn‘t correspond to a hash entry, the value returned depends on the style of new used to create the hash. In the first form, the access returns nil. If obj is specified, this single object will be used for all default values. If a block is specified, it will be called with the hash object and the key, and should return the default value. It is the block‘s responsibility to store the value in the hash if required. 

   h = Hash.new("Go Fish")
   h["a"] = 100
   h["b"] = 200
   h["a"]           #=> 100
   h["c"]           #=> "Go Fish"
   # The following alters the single default object
   h["c"].upcase!   #=> "GO FISH"
   h["d"]           #=> "GO FISH"
   h.keys           #=> ["a", "b"]

   # While this creates a new default object each time
   h = Hash.new { |hash, key| hash[key] = "Go Fish: #{key}" }
   h["c"]           #=> "Go Fish: c"
   h["c"].upcase!   #=> "GO FISH: C"
   h["d"]           #=> "Go Fish: d"
   h.keys           #=> ["c", "d"]

Instance Method Detail

hsh == other_hash => true or false

Equality—Two hashes are equal if they each contain the same number of keys and if each key-value pair is equal to (according to Object#==) the corresponding elements in the other hash. 

   h1 = { "a" => 1, "c" => 2 }
   h2 = { 7 => 35, "c" => 2, "a" => 1 }
   h3 = { "a" => 1, "c" => 2, 7 => 35 }
   h4 = { "a" => 1, "d" => 2, "f" => 35 }
   h1 == h2   #=> false
   h2 == h3   #=> true
   h3 == h4   #=> false

hsh[key] => value

Element Reference—Retrieves the value object corresponding to the key object. If not found, returns the a default value (see Hash::new for details). 

   h = { "a" => 100, "b" => 200 }
   h["a"]   #=> 100
   h["c"]   #=> nil

hsh[key] = value => value
hsh.store(key, value) => value

Element Assignment—Associates the value given by value with the key given by key. key should not have its value changed while it is in use as a key (a String passed as a key will be duplicated and frozen). 

   h = { "a" => 100, "b" => 200 }
   h["a"] = 9
   h["c"] = 4
   h   #=> {"a"=>9, "b"=>200, "c"=>4}

hsh.clear → hsh

Removes all key-value pairs from hsh. 

   h = { "a" => 100, "b" => 200 }   #=> {"a"=>100, "b"=>200}
   h.clear                          #=> {}

hsh.default(key=nil) => obj

Returns the default value, the value that would be returned by hsh[key] if key did not exist in hsh. See also Hash::new and Hash#default=. 

   h = Hash.new                            #=> {}
   h.default                               #=> nil
   h.default(2)                            #=> nil

   h = Hash.new("cat")                     #=> {}
   h.default                               #=> "cat"
   h.default(2)                            #=> "cat"

   h = Hash.new {|h,k| h[k] = k.to_i*10}   #=> {}
   h.default                               #=> nil
   h.default(2)                            #=> 20

hsh.default = obj => hsh

Sets the default value, the value returned for a key that does not exist in the hash. It is not possible to set the a default to a Proc that will be executed on each key lookup. 

   h = { "a" => 100, "b" => 200 }
   h.default = "Go fish"
   h["a"]     #=> 100
   h["z"]     #=> "Go fish"
   # This doesn't do what you might hope...
   h.default = proc do |hash, key|
     hash[key] = key + key
   end
   h[2]       #=> #<Proc:0x401b3948@-:6>
   h["cat"]   #=> #<Proc:0x401b3948@-:6>

hsh.default_proc → anObject

If Hash::new was invoked with a block, return that block, otherwise return nil. 

   h = Hash.new {|h,k| h[k] = k*k }   #=> {}
   p = h.default_proc                 #=> #<Proc:0x401b3d08@-:1>
   a = []                             #=> []
   p.call(a, 2)
   a                                  #=> [nil, nil, 4]

hsh.delete(key) => value
hsh.delete(key) {| key | block } => value

Deletes and returns a key-value pair from hsh whose key is equal to key. If the key is not found, returns nil. If the optional code block is given and the key is not found, pass in the key and return the result of block. 

   h = { "a" => 100, "b" => 200 }
   h.delete("a")                              #=> 100
   h.delete("z")                              #=> nil
   h.delete("z") { |el| "#{el} not found" }   #=> "z not found"

hsh.delete_if {| key, value | block } → hsh

Deletes every key-value pair from hsh for which block evaluates to true. 

   h = { "a" => 100, "b" => 200, "c" => 300 }
   h.delete_if {|key, value| key >= "b" }   #=> {"a"=>100}

hsh.each {| key, value | block } → hsh

Calls block once for each key in hsh, passing the key and value to the block as a two-element array. Because of the assignment semantics of block parameters, these elements will be split out if the block has two formal parameters. Also see Hash.each_pair, which will be marginally more efficient for blocks with two parameters. 

   h = { "a" => 100, "b" => 200 }
   h.each {|key, value| puts "#{key} is #{value}" }

produces: 

   a is 100
   b is 200

hsh.each_key {| key | block } → hsh

Calls block once for each key in hsh, passing the key as a parameter. 

   h = { "a" => 100, "b" => 200 }
   h.each_key {|key| puts key }

produces: 

   a
   b

hsh.each_pair {| key_value_array | block } → hsh

Calls block once for each key in hsh, passing the key and value as parameters. 

   h = { "a" => 100, "b" => 200 }
   h.each_pair {|key, value| puts "#{key} is #{value}" }

produces: 

   a is 100
   b is 200

hsh.each_value {| value | block } → hsh

Calls block once for each key in hsh, passing the value as a parameter. 

   h = { "a" => 100, "b" => 200 }
   h.each_value {|value| puts value }

produces: 

   100
   200

hsh.empty? => true or false

Returns true if hsh contains no key-value pairs. 

   {}.empty?   #=> true

hash.eql?(other) → true or false

Returns true if hash and other are both hashes with the same content.

hsh.fetch(key [, default] ) => obj
hsh.fetch(key) {| key | block } => obj

Returns a value from the hash for the given key. If the key can‘t be found, there are several options: With no other arguments, it will raise an IndexError exception; if default is given, then that will be returned; if the optional code block is specified, then that will be run and its result returned. 

   h = { "a" => 100, "b" => 200 }
   h.fetch("a")                            #=> 100
   h.fetch("z", "go fish")                 #=> "go fish"
   h.fetch("z") { |el| "go fish, #{el}"}   #=> "go fish, z"

The following example shows that an exception is raised if the key is not found and a default value is not supplied. 

   h = { "a" => 100, "b" => 200 }
   h.fetch("z")

produces: 

   prog.rb:2:in `fetch': key not found (IndexError)
    from prog.rb:2

hsh.has_key?(key) => true or false
hsh.include?(key) => true or false
hsh.key?(key) => true or false
hsh.member?(key) => true or false

Returns true if the given key is present in hsh. 

   h = { "a" => 100, "b" => 200 }
   h.has_key?("a")   #=> true
   h.has_key?("z")   #=> false

hsh.has_value?(value) => true or false
hsh.value?(value) => true or false

Returns true if the given value is present for some key in hsh. 

   h = { "a" => 100, "b" => 200 }
   h.has_value?(100)   #=> true
   h.has_value?(999)   #=> false

array.hash → fixnum

Compute a hash-code for this array. Two arrays with the same content will have the same hash code (and will compare using eql?).

hsh.has_key?(key) => true or false
hsh.include?(key) => true or false
hsh.key?(key) => true or false
hsh.member?(key) => true or false

Returns true if the given key is present in hsh. 

   h = { "a" => 100, "b" => 200 }
   h.has_key?("a")   #=> true
   h.has_key?("z")   #=> false

hsh.index(value) => key

Returns the key for a given value. If not found, returns nil. 

   h = { "a" => 100, "b" => 200 }
   h.index(200)   #=> "b"
   h.index(999)   #=> nil

hsh.indexes(key, ...) => array
hsh.indices(key, ...) => array

Deprecated in favor of Hash#select.

hsh.indexes(key, ...) => array
hsh.indices(key, ...) => array

Deprecated in favor of Hash#select.

hsh.replace(other_hash) → hsh

Replaces the contents of hsh with the contents of other_hash. 

   h = { "a" => 100, "b" => 200 }
   h.replace({ "c" => 300, "d" => 400 })   #=> {"c"=>300, "d"=>400}

hsh.inspect => string

Return the contents of this hash as a string.

hsh.invert → aHash

Returns a new hash created by using hsh‘s values as keys, and the keys as values. 

   h = { "n" => 100, "m" => 100, "y" => 300, "d" => 200, "a" => 0 }
   h.invert   #=> {0=>"a", 100=>"n", 200=>"d", 300=>"y"}

hsh.has_key?(key) => true or false
hsh.include?(key) => true or false
hsh.key?(key) => true or false
hsh.member?(key) => true or false

Returns true if the given key is present in hsh. 

   h = { "a" => 100, "b" => 200 }
   h.has_key?("a")   #=> true
   h.has_key?("z")   #=> false

hsh.keys => array

Returns a new array populated with the keys from this hash. See also Hash#values. 

   h = { "a" => 100, "b" => 200, "c" => 300, "d" => 400 }
   h.keys   #=> ["a", "b", "c", "d"]

hsh.length => fixnum
hsh.size => fixnum

Returns the number of key-value pairs in the hash. 

   h = { "d" => 100, "a" => 200, "v" => 300, "e" => 400 }
   h.length        #=> 4
   h.delete("a")   #=> 200
   h.length        #=> 3

hsh.has_key?(key) => true or false
hsh.include?(key) => true or false
hsh.key?(key) => true or false
hsh.member?(key) => true or false

Returns true if the given key is present in hsh. 

   h = { "a" => 100, "b" => 200 }
   h.has_key?("a")   #=> true
   h.has_key?("z")   #=> false

hsh.merge(other_hash) → a_hash
hsh.merge(other_hash){|key, oldval, newval| block} → a_hash

Returns a new hash containing the contents of other_hash and the contents of hsh, overwriting entries in hsh with duplicate keys with those from other_hash. 

   h1 = { "a" => 100, "b" => 200 }
   h2 = { "b" => 254, "c" => 300 }
   h1.merge(h2)   #=> {"a"=>100, "b"=>254, "c"=>300}
   h1             #=> {"a"=>100, "b"=>200}

hsh.merge!(other_hash) => hsh
hsh.update(other_hash) => hsh
hsh.merge!(other_hash){|key, oldval, newval| block} => hsh
hsh.update(other_hash){|key, oldval, newval| block} => hsh

Adds the contents of other_hash to hsh. If no block is specified entries with duplicate keys are overwritten with the values from other_hash, otherwise the value of each duplicate key is determined by calling the block with the key, its value in hsh and its value in other_hash. 

   h1 = { "a" => 100, "b" => 200 }
   h2 = { "b" => 254, "c" => 300 }
   h1.merge!(h2)   #=> {"a"=>100, "b"=>254, "c"=>300}

   h1 = { "a" => 100, "b" => 200 }
   h2 = { "b" => 254, "c" => 300 }
   h1.merge!(h2) { |key, v1, v2| v1 }
                   #=> {"a"=>100, "b"=>200, "c"=>300}

pretty_print(q)

pretty_print_cycle(q)

hsh.rehash → hsh

Rebuilds the hash based on the current hash values for each key. If values of key objects have changed since they were inserted, this method will reindex hsh. If Hash#rehash is called while an iterator is traversing the hash, an IndexError will be raised in the iterator. 

   a = [ "a", "b" ]
   c = [ "c", "d" ]
   h = { a => 100, c => 300 }
   h[a]       #=> 100
   a[0] = "z"
   h[a]       #=> nil
   h.rehash   #=> {["z", "b"]=>100, ["c", "d"]=>300}
   h[a]       #=> 100

hsh.reject {| key, value | block } → a_hash

Same as Hash#delete_if, but works on (and returns) a copy of the hsh. Equivalent to hsh.dup.delete_if.

hsh.reject! {| key, value | block } → hsh or nil

Equivalent to Hash#delete_if, but returns nil if no changes were made.

hsh.replace(other_hash) → hsh

Replaces the contents of hsh with the contents of other_hash. 

   h = { "a" => 100, "b" => 200 }
   h.replace({ "c" => 300, "d" => 400 })   #=> {"c"=>300, "d"=>400}

hsh.select {|key, value| block} => array

Returns a new array consisting of [key,value] pairs for which the block returns true. Also see Hash.values_at. 

   h = { "a" => 100, "b" => 200, "c" => 300 }
   h.select {|k,v| k > "a"}  #=> [["b", 200], ["c", 300]]
   h.select {|k,v| v < 200}  #=> [["a", 100]]

hsh.shift → anArray or obj

Removes a key-value pair from hsh and returns it as the two-item array [ key, value ], or the hash‘s default value if the hash is empty. 

   h = { 1 => "a", 2 => "b", 3 => "c" }
   h.shift   #=> [1, "a"]
   h         #=> {2=>"b", 3=>"c"}

hsh.length => fixnum
hsh.size => fixnum

Returns the number of key-value pairs in the hash. 

   h = { "d" => 100, "a" => 200, "v" => 300, "e" => 400 }
   h.length        #=> 4
   h.delete("a")   #=> 200
   h.length        #=> 3

hsh.sort => array
hsh.sort {| a, b | block } => array

Converts hsh to a nested array of [ key, value ] arrays and sorts it, using Array#sort. 

   h = { "a" => 20, "b" => 30, "c" => 10  }
   h.sort                       #=> [["a", 20], ["b", 30], ["c", 10]]
   h.sort {|a,b| a[1]<=>b[1]}   #=> [["c", 10], ["a", 20], ["b", 30]]

hsh[key] = value => value
hsh.store(key, value) => value

Element Assignment—Associates the value given by value with the key given by key. key should not have its value changed while it is in use as a key (a String passed as a key will be duplicated and frozen). 

   h = { "a" => 100, "b" => 200 }
   h["a"] = 9
   h["c"] = 4
   h   #=> {"a"=>9, "b"=>200, "c"=>4}

hsh.to_a → array

Converts hsh to a nested array of [ key, value ] arrays. 

   h = { "c" => 300, "a" => 100, "d" => 400, "c" => 300  }
   h.to_a   #=> [["a", 100], ["c", 300], ["d", 400]]

hsh.to_hash => hsh

Returns self.

hsh.to_s => string

Converts hsh to a string by converting the hash to an array of [ key, value ] pairs and then converting that array to a string using Array#join with the default separator. 

   h = { "c" => 300, "a" => 100, "d" => 400, "c" => 300  }
   h.to_s   #=> "a100c300d400"

to_yaml( opts = {} )

hsh.merge!(other_hash) => hsh
hsh.update(other_hash) => hsh
hsh.merge!(other_hash){|key, oldval, newval| block} => hsh
hsh.update(other_hash){|key, oldval, newval| block} => hsh

Adds the contents of other_hash to hsh. If no block is specified entries with duplicate keys are overwritten with the values from other_hash, otherwise the value of each duplicate key is determined by calling the block with the key, its value in hsh and its value in other_hash. 

   h1 = { "a" => 100, "b" => 200 }
   h2 = { "b" => 254, "c" => 300 }
   h1.merge!(h2)   #=> {"a"=>100, "b"=>254, "c"=>300}

   h1 = { "a" => 100, "b" => 200 }
   h2 = { "b" => 254, "c" => 300 }
   h1.merge!(h2) { |key, v1, v2| v1 }
                   #=> {"a"=>100, "b"=>200, "c"=>300}

hsh.has_value?(value) => true or false
hsh.value?(value) => true or false

Returns true if the given value is present for some key in hsh. 

   h = { "a" => 100, "b" => 200 }
   h.has_value?(100)   #=> true
   h.has_value?(999)   #=> false

hsh.values => array

Returns a new array populated with the values from hsh. See also Hash#keys. 

   h = { "a" => 100, "b" => 200, "c" => 300 }
   h.values   #=> [100, 200, 300]

hsh.values_at(key, ...) => array

Return an array containing the values associated with the given keys. Also see Hash.select. 

  h = { "cat" => "feline", "dog" => "canine", "cow" => "bovine" }
  h.values_at("cow", "cat")  #=> ["bovine", "feline"]

yaml_initialize( tag, val )