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    Hash

    A is a dictionary-like collection of unique keys and their values. Also called associative arrays, they are similar to Arrays, but where an uses integers as its index, a allows you to use any object type.

    Hashes enumerate their values in the order that the corresponding keys were inserted.

    A can be easily created by using its implicit form: 

    grades = { "Jane Doe" => 10, "Jim Doe" => 6 }

    Hashes allow an alternate syntax for keys that are symbols. Instead of 

    options = { :font_size => 10, :font_family => "Arial" }

    You could write it as: 

    options = { font_size: 10, font_family: "Arial" }

    Each named key is a symbol you can access in hash: 

    options[:font_size] # => 10

    A can also be created through its method: 

    grades = Hash.new
grades["Dorothy Doe"] = 9

    Hashes have a default value that is returned when accessing keys that do not exist in the hash. If no default is set nil is used. You can set the default value by sending it as an argument to : 

    grades = Hash.new(0)

    Or by using the method: 

    grades = {"Timmy Doe" => 8}
grades.default = 0

    Accessing a value in a requires using its key: 

    puts grades["Jane Doe"] # => 0

    Common Uses

    Hashes are an easy way to represent data structures, such as 

    books = {}
books[:matz] = "The Ruby Programming Language"
books[:black] = "The Well-Grounded Rubyist"

    Hashes are also commonly used as a way to have named parameters in functions. Note that no brackets are used below. If a hash is the last argument on a method call, no braces are needed, thus creating a really clean interface: 

    Person.create(name: "John Doe", age: 27)
def self.create(params)
 @name = params[:name]
 @age = params[:age]
end

    Keys

    Two objects refer to the same hash key when their hash value is identical and the two objects are eql? to each other.

    A user-defined class may be used as a hash key if the hash and eql? methods are overridden to provide meaningful behavior. By default, separate instances refer to separate hash keys.

    A typical implementation of hash is based on the object's data while eql? is usually aliased to the overridden == method: 

    class Book
 attr_reader :author, :title
 def initialize(author, title)
 @author = author
 @title = title
 end
 def ==(other)
 self.class === other and
 other.author == @author and
 other.title == @title
 end
 alias eql? ==
 def hash
 @author.hash ^ @title.hash # XOR
 end
end
book1 = Book.new 'matz', 'Ruby in a Nutshell'
book2 = Book.new 'matz', 'Ruby in a Nutshell'
reviews = {}
reviews[book1] = 'Great reference!'
reviews[book2] = 'Nice and compact!'
reviews.length #=> 1

    See also Object#hash and

    Public Class Methods

    Hash[ key, value, ... ] → new_hash click to toggle source
    Hash[ [ [key, value], ... ] ] → new_hash
    Hash[ object ] → new_hash

    Creates a new hash populated with the given objects.

    Similar to the literal { key => value, ... }. In the first form, keys and values occur in pairs, so there must be an even number of arguments.

    The second and third form take a single argument which is either an array of key-value pairs or an object convertible to a hash. 

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

     static VALUE
rb_hash_s_create(int argc, VALUE *argv, VALUE klass)
{
 VALUE hash, tmp;
 if (argc == 1) {
 tmp = rb_hash_s_try_convert(Qnil, argv[0]);
 if (!NIL_P(tmp)) {
 hash = hash_alloc(klass);
 if (RHASH_AR_TABLE_P(tmp)) {
 ar_copy(hash, tmp);
 }
 else {
 RHASH_ST_TABLE_SET(hash, st_copy(RHASH_ST_TABLE(tmp)));
 }
 return hash;
 }
 tmp = rb_check_array_type(argv[0]);
 if (!NIL_P(tmp)) {
 long i;
 hash = hash_alloc(klass);
 for (i = 0; i < RARRAY_LEN(tmp); ++i) {
 VALUE e = RARRAY_AREF(tmp, i);
 VALUE v = rb_check_array_type(e);
 VALUE key, val = Qnil;
 if (NIL_P(v)) {
#if 0 /* refix in the next release */
 rb_raise(rb_eArgError, "wrong element type %s at %ld (expected array)",
 rb_builtin_class_name(e), i);
#else
 rb_warn("wrong element type %s at %ld (expected array)",
 rb_builtin_class_name(e), i);
 rb_warn("ignoring wrong elements is deprecated, remove them explicitly");
 rb_warn("this causes ArgumentError in the next release");
 continue;
#endif
 }
 switch (RARRAY_LEN(v)) {
 default:
 rb_raise(rb_eArgError, "invalid number of elements (%ld for 1..2)",
 RARRAY_LEN(v));
 case 2:
 val = RARRAY_AREF(v, 1);
 case 1:
 key = RARRAY_AREF(v, 0);
 rb_hash_aset(hash, key, val);
 }
 }
 return hash;
 }
 }
 if (argc % 2 != 0) {
 rb_raise(rb_eArgError, "odd number of arguments for Hash");
 }
 hash = hash_alloc(klass);
 rb_hash_bulk_insert(argc, argv, hash);
 hash_verify(hash);
 return hash;
}
    new → new_hash click to toggle source
    new(obj) → new_hash
    new {|hash, key| block } → new_hash

    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"]

     static VALUE
rb_hash_initialize(int argc, VALUE *argv, VALUE hash)
{
 VALUE ifnone;
 rb_hash_modify(hash);
 if (rb_block_given_p()) {
 rb_check_arity(argc, 0, 0);
 ifnone = rb_block_proc();
 SET_PROC_DEFAULT(hash, ifnone);
 }
 else {
 rb_check_arity(argc, 0, 1);
 ifnone = argc == 0 ? Qnil : argv[0];
 RHASH_SET_IFNONE(hash, ifnone);
 }
 return hash;
}
    try_convert(obj) → hash or nil click to toggle source

    Try to convert obj into a hash, using method. Returns converted hash or nil if obj cannot be converted for any reason. 

    Hash.try_convert({1=>2}) # => {1=>2}
Hash.try_convert("1=>2") # => nil

     static VALUE
rb_hash_s_try_convert(VALUE dummy, VALUE hash)
{
 return rb_check_hash_type(hash);
}

    Public Instance Methods

    hash < other → true or false click to toggle source

    Returns true if hash is subset of other. 

    h1 = {a:1, b:2}
h2 = {a:1, b:2, c:3}
h1 < h2 #=> true
h2 < h1 #=> false
h1 < h1 #=> false

     static VALUE
rb_hash_lt(VALUE hash, VALUE other)
{
 other = to_hash(other);
 if (RHASH_SIZE(hash) >= RHASH_SIZE(other)) return Qfalse;
 return hash_le(hash, other);
}
    hash <= other → true or false click to toggle source

    Returns true if hash is subset of other or equals to other. 

    h1 = {a:1, b:2}
h2 = {a:1, b:2, c:3}
h1 <= h2 #=> true
h2 <= h1 #=> false
h1 <= h1 #=> true

     static VALUE
rb_hash_le(VALUE hash, VALUE other)
{
 other = to_hash(other);
 if (RHASH_SIZE(hash) > RHASH_SIZE(other)) return Qfalse;
 return hash_le(hash, other);
}
    hsh == other_hash → true or false click to toggle source

    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

    The orders of each hashes are not compared. 

    h1 = { "a" => 1, "c" => 2 }
h2 = { "c" => 2, "a" => 1 }
h1 == h2 #=> true

     static VALUE
rb_hash_equal(VALUE hash1, VALUE hash2)
{
 return hash_equal(hash1, hash2, FALSE);
}
    hash > other → true or false click to toggle source

    Returns true if other is subset of hash. 

    h1 = {a:1, b:2}
h2 = {a:1, b:2, c:3}
h1 > h2 #=> false
h2 > h1 #=> true
h1 > h1 #=> false

     static VALUE
rb_hash_gt(VALUE hash, VALUE other)
{
 other = to_hash(other);
 if (RHASH_SIZE(hash) <= RHASH_SIZE(other)) return Qfalse;
 return hash_le(other, hash);
}
    hash >= other → true or false click to toggle source

    Returns true if other is subset of hash or equals to hash. 

    h1 = {a:1, b:2}
h2 = {a:1, b:2, c:3}
h1 >= h2 #=> false
h2 >= h1 #=> true
h1 >= h1 #=> true

     static VALUE
rb_hash_ge(VALUE hash, VALUE other)
{
 other = to_hash(other);
 if (RHASH_SIZE(hash) < RHASH_SIZE(other)) return Qfalse;
 return hash_le(other, hash);
}
    hsh[key] → value click to toggle source

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

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

     VALUE
rb_hash_aref(VALUE hash, VALUE key)
{
 st_data_t val;
 if (RHASH_AR_TABLE_P(hash) && ar_lookup(hash, key, &val)) {
 return (VALUE)val;
 }
 else if (RHASH_ST_TABLE_P(hash) && st_lookup(RHASH_ST_TABLE(hash), key, &val)) {
 return (VALUE)val;
 }
 hash_verify(hash);
 return rb_hash_default_value(hash, key);
}
    hsh[key] = value → value click to toggle source

    Element Assignment

    Associates the value given by value with the key given by key. 

    h = { "a" => 100, "b" => 200 }
h["a"] = 9
h["c"] = 4
h #=> {"a"=>9, "b"=>200, "c"=>4}
h.store("d", 42) #=> 42
h #=> {"a"=>9, "b"=>200, "c"=>4, "d"=>42}

    key should not have its value changed while it is in use as a key (an unfrozen String passed as a key will be duplicated and frozen). 

    a = "a"
b = "b".freeze
h = { a => 100, b => 200 }
h.key(100).equal? a #=> false
h.key(200).equal? b #=> true

     VALUE
rb_hash_aset(VALUE hash, VALUE key, VALUE val)
{
 int iter_lev = RHASH_ITER_LEV(hash);
 rb_hash_modify(hash);
 if (RHASH_TABLE_NULL_P(hash)) {
 if (iter_lev > 0) no_new_key();
 ar_alloc_table(hash);
 }
 if (RHASH_TYPE(hash) == &identhash || rb_obj_class(key) != rb_cString) {
 RHASH_UPDATE_ITER(hash, iter_lev, key, hash_aset, val);
 }
 else {
 RHASH_UPDATE_ITER(hash, iter_lev, key, hash_aset_str, val);
 }
 return val;
}
    any? [{ |(key, value)| block }] → true or false click to toggle source
    any?(pattern) → true or false

    See also 

     static VALUE
rb_hash_any_p(int argc, VALUE *argv, VALUE hash)
{
 VALUE args[2];
 args[0] = Qfalse;
 rb_check_arity(argc, 0, 1);
 if (RHASH_EMPTY_P(hash)) return Qfalse;
 if (argc) {
 if (rb_block_given_p()) {
 rb_warn("given block not used");
 }
 args[1] = argv[0];
 rb_hash_foreach(hash, any_p_i_pattern, (VALUE)args);
 }
 else {
 if (!rb_block_given_p()) {
 /* yields pairs, never false */
 return Qtrue;
 }
 if (rb_block_arity() > 1)
 rb_hash_foreach(hash, any_p_i_fast, (VALUE)args);
 else
 rb_hash_foreach(hash, any_p_i, (VALUE)args);
 }
 return args[0];
}
    assoc(obj) → an_array or nil click to toggle source

    Searches through the hash comparing obj with the key using ==. Returns the key-value pair (two elements array) or nil if no match is found. See Array#assoc. 

    h = {"colors" => ["red", "blue", "green"],
 "letters" => ["a", "b", "c" ]}
h.assoc("letters") #=> ["letters", ["a", "b", "c"]]
h.assoc("foo") #=> nil

     VALUE
rb_hash_assoc(VALUE hash, VALUE key)
{
 st_table *table;
 const struct st_hash_type *orighash;
 VALUE args[2];
 if (RHASH_EMPTY_P(hash)) return Qnil;
 ar_force_convert_table(hash, __FILE__, __LINE__);
 HASH_ASSERT(RHASH_ST_TABLE_P(hash));
 table = RHASH_ST_TABLE(hash);
 orighash = table->type;
 if (orighash != &identhash) {
 VALUE value;
 struct reset_hash_type_arg ensure_arg;
 struct st_hash_type assochash;
 assochash.compare = assoc_cmp;
 assochash.hash = orighash->hash;
 table->type = &assochash;
 args[0] = hash;
 args[1] = key;
 ensure_arg.hash = hash;
 ensure_arg.orighash = orighash;
 value = rb_ensure(lookup2_call, (VALUE)&args, reset_hash_type, (VALUE)&ensure_arg);
 if (value != Qundef) return rb_assoc_new(key, value);
 }
 args[0] = key;
 args[1] = Qnil;
 rb_hash_foreach(hash, assoc_i, (VALUE)args);
 return args[1];
}
    clear → hsh click to toggle source

    Removes all key-value pairs from hsh. 

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

     VALUE
rb_hash_clear(VALUE hash)
{
 rb_hash_modify_check(hash);
 if (RHASH_ITER_LEV(hash) > 0) {
 rb_hash_foreach(hash, clear_i, 0);
 }
 else if (RHASH_AR_TABLE_P(hash)) {
 ar_clear(hash);
 }
 else {
 st_clear(RHASH_ST_TABLE(hash));
 }
 return hash;
}
    compact → new_hash click to toggle source

    Returns a new hash with the nil values/key pairs removed 

    h = { a: 1, b: false, c: nil }
h.compact #=> { a: 1, b: false }
h #=> { a: 1, b: false, c: nil }

     static VALUE
rb_hash_compact(VALUE hash)
{
 VALUE result = rb_hash_new();
 if (!RHASH_EMPTY_P(hash)) {
 rb_hash_foreach(hash, set_if_not_nil, result);
 }
 return result;
}
    compact! → hsh or nil click to toggle source

    Removes all nil values from the hash. Returns nil if no changes were made, otherwise returns the hash. 

    h = { a: 1, b: false, c: nil }
h.compact! #=> { a: 1, b: false }

     static VALUE
rb_hash_compact_bang(VALUE hash)
{
 st_index_t n;
 rb_hash_modify_check(hash);
 n = RHASH_SIZE(hash);
 if (n) {
 rb_hash_foreach(hash, delete_if_nil, hash);
 if (n != RHASH_SIZE(hash))
 return hash;
 }
 return Qnil;
}
    compare_by_identity → hsh click to toggle source

    Makes hsh compare its keys by their identity, i.e. it will consider exact same objects as same keys. 

    h1 = { "a" => 100, "b" => 200, :c => "c" }
h1["a"] #=> 100
h1.compare_by_identity
h1.compare_by_identity? #=> true
h1["a".dup] #=> nil # different objects.
h1[:c] #=> "c" # same symbols are all same.

     static VALUE
rb_hash_compare_by_id(VALUE hash)
{
 VALUE tmp;
 st_table *identtable;
 if (rb_hash_compare_by_id_p(hash)) return hash;
 rb_hash_modify_check(hash);
 ar_force_convert_table(hash, __FILE__, __LINE__);
 HASH_ASSERT(RHASH_ST_TABLE_P(hash));
 tmp = hash_alloc(0);
 identtable = rb_init_identtable_with_size(RHASH_SIZE(hash));
 RHASH_ST_TABLE_SET(tmp, identtable);
 rb_hash_foreach(hash, rb_hash_rehash_i, (VALUE)tmp);
 st_free_table(RHASH_ST_TABLE(hash));
 RHASH_ST_TABLE_SET(hash, identtable);
 RHASH_ST_CLEAR(tmp);
 rb_gc_force_recycle(tmp);
 return hash;
}
    compare_by_identity? → true or false click to toggle source

    Returns true if hsh will compare its keys by their identity. Also see Hash#compare_by_identity. 

     MJIT_FUNC_EXPORTED VALUE
rb_hash_compare_by_id_p(VALUE hash)
{
 if (RHASH_ST_TABLE_P(hash) && RHASH_ST_TABLE(hash)->type == &identhash) {
 return Qtrue;
 }
 else {
 return Qfalse;
 }
}
    default(key=nil) → obj click to toggle source

    Returns the default value, the value that would be returned by 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

     static VALUE
rb_hash_default(int argc, VALUE *argv, VALUE hash)
{
 VALUE args[2], ifnone;
 rb_check_arity(argc, 0, 1);
 ifnone = RHASH_IFNONE(hash);
 if (FL_TEST(hash, HASH_PROC_DEFAULT)) {
 if (argc == 0) return Qnil;
 args[0] = hash;
 args[1] = argv[0];
 return rb_funcallv(ifnone, id_yield, 2, args);
 }
 return ifnone;
}
    default = obj → obj click to toggle source

    Sets the default value, the value returned for a key that does not exist in the hash. It is not possible to set the 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>

     static VALUE
rb_hash_set_default(VALUE hash, VALUE ifnone)
{
 rb_hash_modify_check(hash);
 SET_DEFAULT(hash, ifnone);
 return ifnone;
}
    default_proc → anObject click to toggle source

    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]

     static VALUE
rb_hash_default_proc(VALUE hash)
{
 if (FL_TEST(hash, HASH_PROC_DEFAULT)) {
 return RHASH_IFNONE(hash);
 }
 return Qnil;
}
    default_proc = proc_obj or nil click to toggle source

    Sets the default proc to be executed on each failed key lookup. 

    h.default_proc = proc do |hash, key|
 hash[key] = key + key
end
h[2] #=> 4
h["cat"] #=> "catcat"

     VALUE
rb_hash_set_default_proc(VALUE hash, VALUE proc)
{
 VALUE b;
 rb_hash_modify_check(hash);
 if (NIL_P(proc)) {
 SET_DEFAULT(hash, proc);
 return proc;
 }
 b = rb_check_convert_type_with_id(proc, T_DATA, "Proc", idTo_proc);
 if (NIL_P(b) || !rb_obj_is_proc(b)) {
 rb_raise(rb_eTypeError,
 "wrong default_proc type %s (expected Proc)",
 rb_obj_classname(proc));
 }
 proc = b;
 SET_PROC_DEFAULT(hash, proc);
 return proc;
}
    delete(key) → value click to toggle source
    delete(key) {| key | block } → value

    Deletes the key-value pair and returns the value from hsh whose key is equal to key. If the key is not found, it 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"

     static VALUE
rb_hash_delete_m(VALUE hash, VALUE key)
{
 VALUE val;
 rb_hash_modify_check(hash);
 val = rb_hash_delete_entry(hash, key);
 if (val != Qundef) {
 return val;
 }
 else {
 if (rb_block_given_p()) {
 return rb_yield(key);
 }
 else {
 return Qnil;
 }
 }
}
    delete_if {| key, value | block } → hsh click to toggle source
    delete_if → an_enumerator

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

    If no block is given, an enumerator is returned instead. 

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

     VALUE
rb_hash_delete_if(VALUE hash)
{
 RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
 rb_hash_modify_check(hash);
 if (!RHASH_TABLE_EMPTY_P(hash)) {
 rb_hash_foreach(hash, delete_if_i, hash);
 }
 return hash;
}
    dig(key, ...) → object click to toggle source

    Extracts the nested value specified by the sequence of key objects by calling dig at each step, returning nil if any intermediate step is nil. 

    h = { foo: {bar: {baz: 1}}}
h.dig(:foo, :bar, :baz) #=> 1
h.dig(:foo, :zot, :xyz) #=> nil
g = { foo: [10, 11, 12] }
g.dig(:foo, 1) #=> 11
g.dig(:foo, 1, 0) #=> TypeError: Integer does not have #dig method
g.dig(:foo, :bar) #=> TypeError: no implicit conversion of Symbol into Integer

     static VALUE
rb_hash_dig(int argc, VALUE *argv, VALUE self)
{
 rb_check_arity(argc, 1, UNLIMITED_ARGUMENTS);
 self = rb_hash_aref(self, *argv);
 if (!--argc) return self;
 ++argv;
 return rb_obj_dig(argc, argv, self, Qnil);
}
    each {| key, value | block } → hsh click to toggle source
    each_pair {| key, value | block } → hsh
    each → an_enumerator
    each_pair → an_enumerator

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

    If no block is given, an enumerator is returned instead. 

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

    produces: 

    a is 100
b is 200

     static VALUE
rb_hash_each_pair(VALUE hash)
{
 RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
 if (rb_block_arity() > 1)
 rb_hash_foreach(hash, each_pair_i_fast, 0);
 else
 rb_hash_foreach(hash, each_pair_i, 0);
 return hash;
}
    each_key {| key | block } → hsh click to toggle source
    each_key → an_enumerator

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

    If no block is given, an enumerator is returned instead. 

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

    produces: 

    a
b

     static VALUE
rb_hash_each_key(VALUE hash)
{
 RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
 rb_hash_foreach(hash, each_key_i, 0);
 return hash;
}
    each_pair {| key, value | block } → hsh click to toggle source
    each_pair → an_enumerator

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

    If no block is given, an enumerator is returned instead. 

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

    produces: 

    a is 100
b is 200

     static VALUE
rb_hash_each_pair(VALUE hash)
{
 RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
 if (rb_block_arity() > 1)
 rb_hash_foreach(hash, each_pair_i_fast, 0);
 else
 rb_hash_foreach(hash, each_pair_i, 0);
 return hash;
}
    each_value {| value | block } → hsh click to toggle source
    each_value → an_enumerator

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

    If no block is given, an enumerator is returned instead. 

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

    produces: 

    100
200

     static VALUE
rb_hash_each_value(VALUE hash)
{
 RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
 rb_hash_foreach(hash, each_value_i, 0);
 return hash;
}
    empty? → true or false click to toggle source

    Returns true if hsh contains no key-value pairs. 

    {}.empty? #=> true

     static VALUE
rb_hash_empty_p(VALUE hash)
{
 return RHASH_EMPTY_P(hash) ? Qtrue : Qfalse;
}
    eql?(other) → true or false click to toggle source

    Returns true if hash and other are both hashes with the same content. The orders of each hashes are not compared. 

     static VALUE
rb_hash_eql(VALUE hash1, VALUE hash2)
{
 return hash_equal(hash1, hash2, TRUE);
}
    fetch(key [, default] ) → obj click to toggle source
    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 a KeyError 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 (KeyError)
 from prog.rb:2
     static VALUE
rb_hash_fetch_m(int argc, VALUE *argv, VALUE hash)
{
 VALUE key;
 st_data_t val;
 long block_given;
 rb_check_arity(argc, 1, 2);
 key = argv[0];
 block_given = rb_block_given_p();
 if (block_given && argc == 2) {
 rb_warn("block supersedes default value argument");
 }
 if (RHASH_AR_TABLE_P(hash) && ar_lookup(hash, key, &val)) {
 return (VALUE)val;
 }
 else if (RHASH_ST_TABLE_P(hash) && st_lookup(RHASH_ST_TABLE(hash), key, &val)) {
 return (VALUE)val;
 }
 if (block_given) return rb_yield(key);
 if (argc == 1) {
 VALUE desc = rb_protect(rb_inspect, key, 0);
 if (NIL_P(desc)) {
 desc = rb_any_to_s(key);
 }
 desc = rb_str_ellipsize(desc, 65);
 rb_key_err_raise(rb_sprintf("key not found: %"PRIsVALUE, desc), hash, key);
 }
 hash_verify(hash);
 return argv[1];
}
    fetch_values(key, ...) → array click to toggle source
    fetch_values(key, ...) { |key| block } → array

    Returns an array containing the values associated with the given keys but also raises KeyError when one of keys can't be found. Also see Hash#values_at and Hash#fetch. 

    h = { "cat" => "feline", "dog" => "canine", "cow" => "bovine" }
h.fetch_values("cow", "cat") #=> ["bovine", "feline"]
h.fetch_values("cow", "bird") # raises KeyError
h.fetch_values("cow", "bird") { |k| k.upcase } #=> ["bovine", "BIRD"]

     VALUE
rb_hash_fetch_values(int argc, VALUE *argv, VALUE hash)
{
 VALUE result = rb_ary_new2(argc);
 long i;
 for (i=0; i<argc; i++) {
 rb_ary_push(result, rb_hash_fetch(hash, argv[i]));
 }
 return result;
}
    filter {|key, value| block} → a_hash click to toggle source
    filter → an_enumerator

    Returns a new hash consisting of entries for which the block returns true.

    If no block is given, an enumerator is returned instead. 

    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}

    is an alias for . 

     VALUE
rb_hash_select(VALUE hash)
{
 VALUE result;
 RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
 result = rb_hash_new();
 if (!RHASH_EMPTY_P(hash)) {
 rb_hash_foreach(hash, select_i, result);
 }
 return result;
}
    filter! {| key, value | block } → hsh or nil click to toggle source
    filter! → an_enumerator

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

    is an alias for . 

     VALUE
rb_hash_select_bang(VALUE hash)
{
 st_index_t n;
 RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
 rb_hash_modify_check(hash);
 n = RHASH_SIZE(hash);
 if (!n) return Qnil;
 rb_hash_foreach(hash, keep_if_i, hash);
 if (n == RHASH_SIZE(hash)) return Qnil;
 return hash;
}
    flatten → an_array click to toggle source
    flatten(level) → an_array

    Returns a new array that is a one-dimensional flattening of this hash. That is, for every key or value that is an array, extract its elements into the new array. Unlike , this method does not flatten recursively by default. The optional level argument determines the level of recursion to flatten. 

    a = {1=> "one", 2 => [2,"two"], 3 => "three"}
a.flatten # => [1, "one", 2, [2, "two"], 3, "three"]
a.flatten(2) # => [1, "one", 2, 2, "two", 3, "three"]

     static VALUE
rb_hash_flatten(int argc, VALUE *argv, VALUE hash)
{
 VALUE ary;
 rb_check_arity(argc, 0, 1);
 if (argc) {
 int level = NUM2INT(argv[0]);
 if (level == 0) return rb_hash_to_a(hash);
 ary = rb_ary_new_capa(RHASH_SIZE(hash) * 2);
 rb_hash_foreach(hash, flatten_i, ary);
 level--;
 if (level > 0) {
 VALUE ary_flatten_level = INT2FIX(level);
 rb_funcallv(ary, id_flatten_bang, 1, &ary_flatten_level);
 }
 else if (level < 0) {
 /* flatten recursively */
 rb_funcallv(ary, id_flatten_bang, 0, 0);
 }
 }
 else {
 ary = rb_ary_new_capa(RHASH_SIZE(hash) * 2);
 rb_hash_foreach(hash, flatten_i, ary);
 }
 return ary;
}
    has_key?(key) → true or false click to toggle source

    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

    Note that include? and member? do not test member equality using == as do other Enumerables.

    See also 

     MJIT_FUNC_EXPORTED VALUE
rb_hash_has_key(VALUE hash, VALUE key)
{
 if (RHASH_AR_TABLE_P(hash) && ar_lookup(hash, key, 0)) {
 return Qtrue;
 }
 else if (RHASH_ST_TABLE_P(hash) && st_lookup(RHASH_ST_TABLE(hash), key, 0)) {
 return Qtrue;
 }
 return Qfalse;
}
    has_value?(value) → true or false click to toggle source

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

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

     static VALUE
rb_hash_has_value(VALUE hash, VALUE val)
{
 VALUE data[2];
 data[0] = Qfalse;
 data[1] = val;
 rb_hash_foreach(hash, rb_hash_search_value, (VALUE)data);
 return data[0];
}
    hash → integer click to toggle source

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

    See also Object#hash. 

     static VALUE
rb_hash_hash(VALUE hash)
{
 st_index_t size = RHASH_SIZE(hash);
 st_index_t hval = rb_hash_start(size);
 hval = rb_hash_uint(hval, (st_index_t)rb_hash_hash);
 if (size) {
 rb_hash_foreach(hash, hash_i, (VALUE)&hval);
 }
 hval = rb_hash_end(hval);
 return ST2FIX(hval);
}
    include?(key) → true or false click to toggle source

    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

    Note that include? and member? do not test member equality using == as do other Enumerables.

    See also 

     MJIT_FUNC_EXPORTED VALUE
rb_hash_has_key(VALUE hash, VALUE key)
{
 if (RHASH_AR_TABLE_P(hash) && ar_lookup(hash, key, 0)) {
 return Qtrue;
 }
 else if (RHASH_ST_TABLE_P(hash) && st_lookup(RHASH_ST_TABLE(hash), key, 0)) {
 return Qtrue;
 }
 return Qfalse;
}
    to_s → string click to toggle source
    inspect → string

    Return the contents of this hash as a string. 

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

     static VALUE
rb_hash_inspect(VALUE hash)
{
 if (RHASH_EMPTY_P(hash))
 return rb_usascii_str_new2("{}");
 return rb_exec_recursive(inspect_hash, hash, 0);
}
    Also aliased as:
    invert → new_hash click to toggle source

    Returns a new hash created by using hsh's values as keys, and the keys as values. If a key with the same value already exists in the hsh, then the last one defined will be used, the earlier value(s) will be discarded. 

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

    If there is no key with the same value, is involutive. 

    h = { a: 1, b: 3, c: 4 }
h.invert.invert == h #=> true

    The condition, no key with the same value, can be tested by comparing the size of inverted hash. 

    # no key with the same value
h = { a: 1, b: 3, c: 4 }
h.size == h.invert.size #=> true
# two (or more) keys has the same value
h = { a: 1, b: 3, c: 1 }
h.size == h.invert.size #=> false

     static VALUE
rb_hash_invert(VALUE hash)
{
 VALUE h = rb_hash_new_with_size(RHASH_SIZE(hash));
 rb_hash_foreach(hash, rb_hash_invert_i, h);
 return h;
}
    keep_if {| key, value | block } → hsh click to toggle source
    keep_if → an_enumerator

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

    If no block is given, an enumerator is returned instead.

    See also . 

     VALUE
rb_hash_keep_if(VALUE hash)
{
 RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
 rb_hash_modify_check(hash);
 if (!RHASH_TABLE_EMPTY_P(hash)) {
 rb_hash_foreach(hash, keep_if_i, hash);
 }
 return hash;
}
    key(value) → key click to toggle source

    Returns the key of an occurrence of a given value. If the value is not found, returns nil. 

    h = { "a" => 100, "b" => 200, "c" => 300, "d" => 300 }
h.key(200) #=> "b"
h.key(300) #=> "c"
h.key(999) #=> nil

     static VALUE
rb_hash_key(VALUE hash, VALUE value)
{
 VALUE args[2];
 args[0] = value;
 args[1] = Qnil;
 rb_hash_foreach(hash, key_i, (VALUE)args);
 return args[1];
}
    key?(key) → true or false click to toggle source

    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

    Note that include? and member? do not test member equality using == as do other Enumerables.

    See also 

     MJIT_FUNC_EXPORTED VALUE
rb_hash_has_key(VALUE hash, VALUE key)
{
 if (RHASH_AR_TABLE_P(hash) && ar_lookup(hash, key, 0)) {
 return Qtrue;
 }
 else if (RHASH_ST_TABLE_P(hash) && st_lookup(RHASH_ST_TABLE(hash), key, 0)) {
 return Qtrue;
 }
 return Qfalse;
}
    keys → array click to toggle source

    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"]

     MJIT_FUNC_EXPORTED VALUE
rb_hash_keys(VALUE hash)
{
 st_index_t size = RHASH_SIZE(hash);
 VALUE keys = rb_ary_new_capa(size);
 if (size == 0) return keys;
 if (ST_DATA_COMPATIBLE_P(VALUE)) {
 RARRAY_PTR_USE_TRANSIENT(keys, ptr, {
 if (RHASH_AR_TABLE_P(hash)) {
 size = ar_keys(hash, ptr, size);
 }
 else {
 st_table *table = RHASH_ST_TABLE(hash);
 size = st_keys(table, ptr, size);
 }
 });
 rb_gc_writebarrier_remember(keys);
 rb_ary_set_len(keys, size);
 }
 else {
 rb_hash_foreach(hash, keys_i, keys);
 }
 return keys;
}
    length → integer click to toggle source

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

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

    is an alias for . 

     VALUE
rb_hash_size(VALUE hash)
{
 return INT2FIX(RHASH_SIZE(hash));
}
    member?(key) → true or false click to toggle source

    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

    Note that include? and member? do not test member equality using == as do other Enumerables.

    See also 

     MJIT_FUNC_EXPORTED VALUE
rb_hash_has_key(VALUE hash, VALUE key)
{
 if (RHASH_AR_TABLE_P(hash) && ar_lookup(hash, key, 0)) {
 return Qtrue;
 }
 else if (RHASH_ST_TABLE_P(hash) && st_lookup(RHASH_ST_TABLE(hash), key, 0)) {
 return Qtrue;
 }
 return Qfalse;
}
    merge(other_hash1, other_hash2, ...) → new_hash click to toggle source
    merge(other_hash1, other_hash2, ...) {|key, oldval, newval| block}
    → new_hash

    Returns a new hash that combines the contents of the receiver and the contents of the given hashes.

    If no block is given, entries with duplicate keys are overwritten with the values from each other_hash successively, otherwise the value for each duplicate key is determined by calling the block with the key, its value in the receiver and its value in each other_hash.

    When called without any argument, returns a copy of the receiver. 

    h1 = { "a" => 100, "b" => 200 }
h2 = { "b" => 246, "c" => 300 }
h3 = { "b" => 357, "d" => 400 }
h1.merge #=> {"a"=>100, "b"=>200}
h1.merge(h2) #=> {"a"=>100, "b"=>246, "c"=>300}
h1.merge(h2, h3) #=> {"a"=>100, "b"=>357, "c"=>300, "d"=>400}
h1.merge(h2) {|key, oldval, newval| newval - oldval}
 #=> {"a"=>100, "b"=>46, "c"=>300}
h1.merge(h2, h3) {|key, oldval, newval| newval - oldval}
 #=> {"a"=>100, "b"=>311, "c"=>300, "d"=>400}
h1 #=> {"a"=>100, "b"=>200}

     static VALUE
rb_hash_merge(int argc, VALUE *argv, VALUE self)
{
 return rb_hash_update(argc, argv, rb_hash_dup(self));
}
    merge!(other_hash1, other_hash2, ...) → hsh click to toggle source
    merge!(other_hash1, other_hash2, ...) {|key, oldval, newval| block}

    Adds the contents of the given hashes to the receiver.

    If no block is given, entries with duplicate keys are overwritten with the values from each other_hash successively, otherwise the value for each duplicate key is determined by calling the block with the key, its value in the receiver and its value in each other_hash. 

    h1 = { "a" => 100, "b" => 200 }
h1.merge! #=> {"a"=>100, "b"=>200}
h1 #=> {"a"=>100, "b"=>200}
h1 = { "a" => 100, "b" => 200 }
h2 = { "b" => 246, "c" => 300 }
h1.merge!(h2) #=> {"a"=>100, "b"=>246, "c"=>300}
h1 #=> {"a"=>100, "b"=>246, "c"=>300}
h1 = { "a" => 100, "b" => 200 }
h2 = { "b" => 246, "c" => 300 }
h3 = { "b" => 357, "d" => 400 }
h1.merge!(h2, h3)
 #=> {"a"=>100, "b"=>357, "c"=>300, "d"=>400}
h1 #=> {"a"=>100, "b"=>357, "c"=>300, "d"=>400}
h1 = { "a" => 100, "b" => 200 }
h2 = { "b" => 246, "c" => 300 }
h3 = { "b" => 357, "d" => 400 }
h1.merge!(h2, h3) {|key, v1, v2| v1 }
 #=> {"a"=>100, "b"=>200, "c"=>300, "d"=>400}
h1 #=> {"a"=>100, "b"=>200, "c"=>300, "d"=>400}

    is an alias for . 

     static VALUE
rb_hash_update(int argc, VALUE *argv, VALUE self)
{
 int i;
 bool block_given = rb_block_given_p();
 rb_hash_modify(self);
 for (i = 0; i < argc; i++){
 VALUE hash = to_hash(argv[i]);
 if (block_given) {
 rb_hash_foreach(hash, rb_hash_update_block_i, self);
 }
 else {
 rb_hash_foreach(hash, rb_hash_update_i, self);
 }
 }
 return self;
}
    rassoc(obj) → an_array or nil click to toggle source

    Searches through the hash comparing obj with the value using ==. Returns the first key-value pair (two-element array) that matches. See also Array#rassoc. 

    a = {1=> "one", 2 => "two", 3 => "three", "ii" => "two"}
a.rassoc("two") #=> [2, "two"]
a.rassoc("four") #=> nil

     VALUE
rb_hash_rassoc(VALUE hash, VALUE obj)
{
 VALUE args[2];
 args[0] = obj;
 args[1] = Qnil;
 rb_hash_foreach(hash, rassoc_i, (VALUE)args);
 return args[1];
}
    rehash → hsh click to toggle source

    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, a RuntimeError 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

     VALUE
rb_hash_rehash(VALUE hash)
{
 VALUE tmp;
 st_table *tbl;
 if (RHASH_ITER_LEV(hash) > 0) {
 rb_raise(rb_eRuntimeError, "rehash during iteration");
 }
 rb_hash_modify_check(hash);
 if (RHASH_AR_TABLE_P(hash)) {
 tmp = hash_alloc(0);
 ar_alloc_table(tmp);
 rb_hash_foreach(hash, rb_hash_rehash_i, (VALUE)tmp);
 ar_free_and_clear_table(hash);
 ar_copy(hash, tmp);
 ar_free_and_clear_table(tmp);
 }
 else if (RHASH_ST_TABLE_P(hash)) {
 st_table *old_tab = RHASH_ST_TABLE(hash);
 tmp = hash_alloc(0);
 tbl = st_init_table_with_size(old_tab->type, old_tab->num_entries);
 RHASH_ST_TABLE_SET(tmp, tbl);
 rb_hash_foreach(hash, rb_hash_rehash_i, (VALUE)tmp);
 st_free_table(old_tab);
 RHASH_ST_TABLE_SET(hash, tbl);
 RHASH_ST_CLEAR(tmp);
 }
 hash_verify(hash);
 return hash;
}
    reject {|key, value| block} → a_hash click to toggle source
    reject → an_enumerator

    Returns a new hash consisting of entries for which the block returns false.

    If no block is given, an enumerator is returned instead. 

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

     VALUE
rb_hash_reject(VALUE hash)
{
 VALUE result;
 RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
 if (RTEST(ruby_verbose)) {
 VALUE klass;
 if (HAS_EXTRA_STATES(hash, klass)) {
 rb_warn("extra states are no longer copied: %+"PRIsVALUE, hash);
 }
 }
 result = rb_hash_new();
 if (!RHASH_EMPTY_P(hash)) {
 rb_hash_foreach(hash, reject_i, result);
 }
 return result;
}
    reject! {| key, value | block } → hsh or nil click to toggle source
    reject! → an_enumerator

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

     VALUE
rb_hash_reject_bang(VALUE hash)
{
 st_index_t n;
 RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
 rb_hash_modify(hash);
 n = RHASH_SIZE(hash);
 if (!n) return Qnil;
 rb_hash_foreach(hash, delete_if_i, hash);
 if (n == RHASH_SIZE(hash)) return Qnil;
 return hash;
}
    replace(other_hash) → hsh click to toggle source

    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}

     static VALUE
rb_hash_replace(VALUE hash, VALUE hash2)
{
 rb_hash_modify_check(hash);
 if (hash == hash2) return hash;
 hash2 = to_hash(hash2);
 COPY_DEFAULT(hash, hash2);
 rb_hash_clear(hash);
 if (RHASH_AR_TABLE_P(hash)) {
 if (RHASH_AR_TABLE_P(hash2)) {
 ar_copy(hash, hash2);
 }
 else {
 goto st_to_st;
 }
 }
 else {
 if (RHASH_AR_TABLE_P(hash2)) ar_force_convert_table(hash2, __FILE__, __LINE__);
 st_to_st:
 RHASH_TBL_RAW(hash)->type = RHASH_ST_TABLE(hash2)->type;
 rb_hash_foreach(hash2, replace_i, hash);
 }
 return hash;
}
    select {|key, value| block} → a_hash click to toggle source
    select → an_enumerator

    Returns a new hash consisting of entries for which the block returns true.

    If no block is given, an enumerator is returned instead. 

    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}

    is an alias for . 

     VALUE
rb_hash_select(VALUE hash)
{
 VALUE result;
 RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
 result = rb_hash_new();
 if (!RHASH_EMPTY_P(hash)) {
 rb_hash_foreach(hash, select_i, result);
 }
 return result;
}
    select! {| key, value | block } → hsh or nil click to toggle source
    select! → an_enumerator

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

    is an alias for . 

     VALUE
rb_hash_select_bang(VALUE hash)
{
 st_index_t n;
 RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
 rb_hash_modify_check(hash);
 n = RHASH_SIZE(hash);
 if (!n) return Qnil;
 rb_hash_foreach(hash, keep_if_i, hash);
 if (n == RHASH_SIZE(hash)) return Qnil;
 return hash;
}
    shift → anArray or obj click to toggle source

    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"}

     static VALUE
rb_hash_shift(VALUE hash)
{
 struct shift_var var;
 rb_hash_modify_check(hash);
 if (RHASH_AR_TABLE_P(hash)) {
 var.key = Qundef;
 if (RHASH_ITER_LEV(hash) == 0) {
 if (ar_shift(hash, &var.key, &var.val)) {
 return rb_assoc_new(var.key, var.val);
 }
 }
 else {
 rb_hash_foreach(hash, shift_i_safe, (VALUE)&var);
 if (var.key != Qundef) {
 rb_hash_delete_entry(hash, var.key);
 return rb_assoc_new(var.key, var.val);
 }
 }
 }
 if (RHASH_ST_TABLE_P(hash)) {
 var.key = Qundef;
 if (RHASH_ITER_LEV(hash) == 0) {
 if (st_shift(RHASH_ST_TABLE(hash), &var.key, &var.val)) {
 return rb_assoc_new(var.key, var.val);
 }
 }
 else {
 rb_hash_foreach(hash, shift_i_safe, (VALUE)&var);
 if (var.key != Qundef) {
 rb_hash_delete_entry(hash, var.key);
 return rb_assoc_new(var.key, var.val);
 }
 }
 }
 return rb_hash_default_value(hash, Qnil);
}
    size → integer click to toggle source

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

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

    is an alias for . 

     VALUE
rb_hash_size(VALUE hash)
{
 return INT2FIX(RHASH_SIZE(hash));
}
    slice(*keys) → a_hash click to toggle source

    Returns a hash containing only the given keys and their values. 

    h = { a: 100, b: 200, c: 300 }
h.slice(:a) #=> {:a=>100}
h.slice(:b, :c, :d) #=> {:b=>200, :c=>300}

     static VALUE
rb_hash_slice(int argc, VALUE *argv, VALUE hash)
{
 int i;
 VALUE key, value, result;
 if (argc == 0 || RHASH_EMPTY_P(hash)) {
 return rb_hash_new();
 }
 result = rb_hash_new_with_size(argc);
 for (i = 0; i < argc; i++) {
 key = argv[i];
 value = rb_hash_lookup2(hash, key, Qundef);
 if (value != Qundef)
 rb_hash_aset(result, key, value);
 }
 return result;
}
    store(key, value) → value click to toggle source

    Element Assignment

    Associates the value given by value with the key given by key. 

    h = { "a" => 100, "b" => 200 }
h["a"] = 9
h["c"] = 4
h #=> {"a"=>9, "b"=>200, "c"=>4}
h.store("d", 42) #=> 42
h #=> {"a"=>9, "b"=>200, "c"=>4, "d"=>42}

    key should not have its value changed while it is in use as a key (an unfrozen String passed as a key will be duplicated and frozen). 

    a = "a"
b = "b".freeze
h = { a => 100, b => 200 }
h.key(100).equal? a #=> false
h.key(200).equal? b #=> true

     VALUE
rb_hash_aset(VALUE hash, VALUE key, VALUE val)
{
 int iter_lev = RHASH_ITER_LEV(hash);
 rb_hash_modify(hash);
 if (RHASH_TABLE_NULL_P(hash)) {
 if (iter_lev > 0) no_new_key();
 ar_alloc_table(hash);
 }
 if (RHASH_TYPE(hash) == &identhash || rb_obj_class(key) != rb_cString) {
 RHASH_UPDATE_ITER(hash, iter_lev, key, hash_aset, val);
 }
 else {
 RHASH_UPDATE_ITER(hash, iter_lev, key, hash_aset_str, val);
 }
 return val;
}
    to_a → array click to toggle source

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

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

     static VALUE
rb_hash_to_a(VALUE hash)
{
 VALUE ary;
 ary = rb_ary_new_capa(RHASH_SIZE(hash));
 rb_hash_foreach(hash, to_a_i, ary);
 OBJ_INFECT(ary, hash);
 return ary;
}
    to_h → hsh or new_hash click to toggle source
    to_h {|key, value| block } → new_hash

    Returns self. If called on a subclass of , converts the receiver to a object.

    If a block is given, the results of the block on each pair of the receiver will be used as pairs. 

     static VALUE
rb_hash_to_h(VALUE hash)
{
 if (rb_block_given_p()) {
 return rb_hash_to_h_block(hash);
 }
 if (rb_obj_class(hash) != rb_cHash) {
 const VALUE flags = RBASIC(hash)->flags;
 hash = hash_dup(hash, rb_cHash, flags & HASH_PROC_DEFAULT);
 }
 return hash;
}
    to_hash => hsh click to toggle source

    Returns self. 

     static VALUE
rb_hash_to_hash(VALUE hash)
{
 return hash;
}
    to_proc → proc click to toggle source

    Returns a which maps keys to values. 

    h = {a:1, b:2}
hp = h.to_proc
hp.call(:a) #=> 1
hp.call(:b) #=> 2
hp.call(:c) #=> nil
[:a, :b, :c].map(&h) #=> [1, 2, nil]

     static VALUE
rb_hash_to_proc(VALUE hash)
{
 return rb_func_proc_new(hash_proc_call, hash);
}
    to_s() click to toggle source
    Alias for:
    transform_keys {|key| block } → new_hash click to toggle source
    transform_keys → an_enumerator

    Returns a new hash with the results of running the block once for every key. This method does not change the values. 

    h = { a: 1, b: 2, c: 3 }
h.transform_keys {|k| k.to_s } #=> { "a" => 1, "b" => 2, "c" => 3 }
h.transform_keys(&:to_s) #=> { "a" => 1, "b" => 2, "c" => 3 }
h.transform_keys.with_index {|k, i| "#{k}.#{i}" }
 #=> { "a.0" => 1, "b.1" => 2, "c.2" => 3 }

    If no block is given, an enumerator is returned instead. 

     static VALUE
rb_hash_transform_keys(VALUE hash)
{
 VALUE result;
 RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
 result = rb_hash_new();
 if (!RHASH_EMPTY_P(hash)) {
 rb_hash_foreach(hash, transform_keys_i, result);
 }
 return result;
}
    transform_keys! {|key| block } → hsh click to toggle source
    transform_keys! → an_enumerator

    Invokes the given block once for each key in hsh, replacing it with the new key returned by the block, and then returns hsh. This method does not change the values. 

    h = { a: 1, b: 2, c: 3 }
h.transform_keys! {|k| k.to_s } #=> { "a" => 1, "b" => 2, "c" => 3 }
h.transform_keys!(&:to_sym) #=> { a: 1, b: 2, c: 3 }
h.transform_keys!.with_index {|k, i| "#{k}.#{i}" }
 #=> { "a.0" => 1, "b.1" => 2, "c.2" => 3 }

    If no block is given, an enumerator is returned instead. 

     static VALUE
rb_hash_transform_keys_bang(VALUE hash)
{
 RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
 rb_hash_modify_check(hash);
 if (!RHASH_TABLE_EMPTY_P(hash)) {
 long i;
 VALUE pairs = rb_hash_flatten(0, NULL, hash);
 rb_hash_clear(hash);
 for (i = 0; i < RARRAY_LEN(pairs); i += 2) {
 VALUE key = RARRAY_AREF(pairs, i), new_key = rb_yield(key),
 val = RARRAY_AREF(pairs, i+1);
 rb_hash_aset(hash, new_key, val);
 }
 }
 return hash;
}
    transform_values {|value| block } → new_hash click to toggle source
    transform_values → an_enumerator

    Returns a new hash with the results of running the block once for every value. This method does not change the keys. 

    h = { a: 1, b: 2, c: 3 }
h.transform_values {|v| v * v + 1 } #=> { a: 2, b: 5, c: 10 }
h.transform_values(&:to_s) #=> { a: "1", b: "2", c: "3" }
h.transform_values.with_index {|v, i| "#{v}.#{i}" }
 #=> { a: "1.0", b: "2.1", c: "3.2" }

    If no block is given, an enumerator is returned instead. 

     static VALUE
rb_hash_transform_values(VALUE hash)
{
 VALUE result;
 RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
 result = rb_hash_new_with_size(RHASH_SIZE(hash));
 if (!RHASH_EMPTY_P(hash)) {
 rb_hash_foreach(hash, transform_values_i, result);
 }
 return result;
}
    transform_values! {|value| block } → hsh click to toggle source
    transform_values! → an_enumerator

    Invokes the given block once for each value in hsh, replacing it with the new value returned by the block, and then returns hsh. This method does not change the keys. 

    h = { a: 1, b: 2, c: 3 }
h.transform_values! {|v| v * v + 1 } #=> { a: 2, b: 5, c: 10 }
h.transform_values!(&:to_s) #=> { a: "2", b: "5", c: "10" }
h.transform_values!.with_index {|v, i| "#{v}.#{i}" }
 #=> { a: "2.0", b: "5.1", c: "10.2" }

    If no block is given, an enumerator is returned instead. 

     static VALUE
rb_hash_transform_values_bang(VALUE hash)
{
 RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
 rb_hash_modify_check(hash);
 if (!RHASH_TABLE_EMPTY_P(hash))
 rb_hash_foreach(hash, transform_values_i, hash);
 return hash;
}
    update(other_hash1, other_hash2, ...) → hsh click to toggle source
    update(other_hash1, other_hash2, ...) {|key, oldval, newval| block}

    Adds the contents of the given hashes to the receiver.

    If no block is given, entries with duplicate keys are overwritten with the values from each other_hash successively, otherwise the value for each duplicate key is determined by calling the block with the key, its value in the receiver and its value in each other_hash. 

    h1 = { "a" => 100, "b" => 200 }
h1.merge! #=> {"a"=>100, "b"=>200}
h1 #=> {"a"=>100, "b"=>200}
h1 = { "a" => 100, "b" => 200 }
h2 = { "b" => 246, "c" => 300 }
h1.merge!(h2) #=> {"a"=>100, "b"=>246, "c"=>300}
h1 #=> {"a"=>100, "b"=>246, "c"=>300}
h1 = { "a" => 100, "b" => 200 }
h2 = { "b" => 246, "c" => 300 }
h3 = { "b" => 357, "d" => 400 }
h1.merge!(h2, h3)
 #=> {"a"=>100, "b"=>357, "c"=>300, "d"=>400}
h1 #=> {"a"=>100, "b"=>357, "c"=>300, "d"=>400}
h1 = { "a" => 100, "b" => 200 }
h2 = { "b" => 246, "c" => 300 }
h3 = { "b" => 357, "d" => 400 }
h1.merge!(h2, h3) {|key, v1, v2| v1 }
 #=> {"a"=>100, "b"=>200, "c"=>300, "d"=>400}
h1 #=> {"a"=>100, "b"=>200, "c"=>300, "d"=>400}

    is an alias for . 

     static VALUE
rb_hash_update(int argc, VALUE *argv, VALUE self)
{
 int i;
 bool block_given = rb_block_given_p();
 rb_hash_modify(self);
 for (i = 0; i < argc; i++){
 VALUE hash = to_hash(argv[i]);
 if (block_given) {
 rb_hash_foreach(hash, rb_hash_update_block_i, self);
 }
 else {
 rb_hash_foreach(hash, rb_hash_update_i, self);
 }
 }
 return self;
}
    value?(value) → true or false click to toggle source

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

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

     static VALUE
rb_hash_has_value(VALUE hash, VALUE val)
{
 VALUE data[2];
 data[0] = Qfalse;
 data[1] = val;
 rb_hash_foreach(hash, rb_hash_search_value, (VALUE)data);
 return data[0];
}
    values → array click to toggle source

    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]

     VALUE
rb_hash_values(VALUE hash)
{
 VALUE values;
 st_index_t size = RHASH_SIZE(hash);
 values = rb_ary_new_capa(size);
 if (size == 0) return values;
 if (ST_DATA_COMPATIBLE_P(VALUE)) {
 if (RHASH_AR_TABLE_P(hash)) {
 rb_gc_writebarrier_remember(values);
 RARRAY_PTR_USE_TRANSIENT(values, ptr, {
 size = ar_values(hash, ptr, size);
 });
 }
 else if (RHASH_ST_TABLE_P(hash)) {
 st_table *table = RHASH_ST_TABLE(hash);
 rb_gc_writebarrier_remember(values);
 RARRAY_PTR_USE_TRANSIENT(values, ptr, {
 size = st_values(table, ptr, size);
 });
 }
 rb_ary_set_len(values, size);
 }
 else {
 rb_hash_foreach(hash, values_i, values);
 }
 return values;
}
    values_at(key, ...) → array click to toggle source

    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"]

     VALUE
rb_hash_values_at(int argc, VALUE *argv, VALUE hash)
{
 VALUE result = rb_ary_new2(argc);
 long i;
 for (i=0; i<argc; i++) {
 rb_ary_push(result, rb_hash_aref(hash, argv[i]));
 }
 return result;
}

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