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
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Included Modules
Class Public methods
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}

Source: show 

static VALUE
rb_hash_s_create(argc, argv, klass)
    int argc;
    VALUE *argv;
    VALUE klass;
{
    VALUE hash, tmp;
    int i;

    if (argc == 1) {
        tmp = rb_check_convert_type(argv[0], T_HASH, "Hash", "to_hash");
        if (!NIL_P(tmp)) {
            hash = hash_alloc0(klass);
            RHASH(hash)->tbl = st_copy(RHASH(tmp)->tbl);
            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 v = rb_check_array_type(RARRAY_PTR(tmp)[i]);
                VALUE key, val = Qnil;

                if (NIL_P(v)) continue;
                switch (RARRAY_LEN(v)) {
                  case 2:
                    val = RARRAY_PTR(v)[1];
                  case 1:
                    key = RARRAY_PTR(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);
    for (i=0; i<argc; i+=2) {
        rb_hash_aset(hash, argv[i], argv[i + 1]);
    }

    return hash;
}
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"]

Source: show 

static VALUE
rb_hash_initialize(argc, argv, hash)
    int argc;
    VALUE *argv;
    VALUE hash;
{
    VALUE ifnone;

    rb_hash_modify(hash);
    if (rb_block_given_p()) {
        if (argc > 0) {
            rb_raise(rb_eArgError, "wrong number of arguments");
        }
        RHASH(hash)->ifnone = rb_block_proc();
        FL_SET(hash, HASH_PROC_DEFAULT);
    }
    else {
        rb_scan_args(argc, argv, "01", &ifnone);
        RHASH(hash)->ifnone = ifnone;
    }

    return hash;
}
Instance Public methods
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

Source: show 

static VALUE
rb_hash_equal(hash1, hash2)
    VALUE hash1, hash2;
{
    return hash_equal(hash1, hash2, Qfalse);
}
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

Source: show 

VALUE
rb_hash_aref(hash, key)
    VALUE hash, key;
{
    VALUE val;

    if (!st_lookup(RHASH(hash)->tbl, key, &val)) {
        return rb_funcall(hash, id_default, 1, key);
    }
    return val;
}
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}

Source: show 

VALUE
rb_hash_aset(hash, key, val)
    VALUE hash, key, val;
{
    rb_hash_modify(hash);
    if (TYPE(key) != T_STRING || st_lookup(RHASH(hash)->tbl, key, 0)) {
        st_insert(RHASH(hash)->tbl, key, val);
    }
    else {
        st_add_direct(RHASH(hash)->tbl, rb_str_new4(key), val);
    }
    return val;
}
hsh.clear → hsh

Removes all key-value pairs from hsh. 

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

Source: show 

static VALUE
rb_hash_clear(hash)
    VALUE hash;
{
    rb_hash_modify(hash);
    if (RHASH(hash)->tbl->num_entries > 0) {
        rb_hash_foreach(hash, clear_i, 0);
    }

    return hash;
}
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

Source: show 

static VALUE
rb_hash_default(argc, argv, hash)
    int argc;
    VALUE *argv;
    VALUE hash;
{
    VALUE key;

    rb_scan_args(argc, argv, "01", &key);
    if (FL_TEST(hash, HASH_PROC_DEFAULT)) {
        if (argc == 0) return Qnil;
        return rb_funcall(RHASH(hash)->ifnone, id_call, 2, hash, key);
    }
    return RHASH(hash)->ifnone;
}
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>

Source: show 

static VALUE
rb_hash_set_default(hash, ifnone)
    VALUE hash, ifnone;
{
    rb_hash_modify(hash);
    RHASH(hash)->ifnone = ifnone;
    FL_UNSET(hash, HASH_PROC_DEFAULT);
    return ifnone;
}
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]

Source: show 

static VALUE
rb_hash_default_proc(hash)
    VALUE hash;
{
    if (FL_TEST(hash, HASH_PROC_DEFAULT)) {
        return RHASH(hash)->ifnone;
    }
    return Qnil;
}
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"

Source: show 

VALUE
rb_hash_delete(hash, key)
    VALUE hash, key;
{
    VALUE val;

    rb_hash_modify(hash);
    val = rb_hash_delete_key(hash, key);
    if (val != Qundef) return val;
    if (rb_block_given_p()) {
        return rb_yield(key);
    }
    return Qnil;
}
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}

Source: show 

VALUE
rb_hash_delete_if(hash)
    VALUE hash;
{
    RETURN_ENUMERATOR(hash, 0, 0);
    rb_hash_modify(hash);
    rb_hash_foreach(hash, delete_if_i, hash);
    return hash;
}
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

Source: show 

static VALUE
rb_hash_each(hash)
    VALUE hash;
{
    RETURN_ENUMERATOR(hash, 0, 0);
    rb_hash_foreach(hash, each_i, 0);
    return hash;
}
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

Source: show 

static VALUE
rb_hash_each_key(hash)
    VALUE hash;
{
    RETURN_ENUMERATOR(hash, 0, 0);
    rb_hash_foreach(hash, each_key_i, 0);
    return hash;
}
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

Source: show 

static VALUE
rb_hash_each_pair(hash)
    VALUE hash;
{
    RETURN_ENUMERATOR(hash, 0, 0);
    rb_hash_foreach(hash, each_pair_i, 0);
    return hash;
}
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

Source: show 

static VALUE
rb_hash_each_value(hash)
    VALUE hash;
{
    RETURN_ENUMERATOR(hash, 0, 0);
    rb_hash_foreach(hash, each_value_i, 0);
    return hash;
}
hsh.empty? => true or false

Returns true if hsh contains no key-value pairs. 

   {}.empty?   #=> true

Source: show 

static VALUE
rb_hash_empty_p(hash)
    VALUE hash;
{
    if (RHASH(hash)->tbl->num_entries == 0)
        return Qtrue;
    return Qfalse;
}
hash.eql?(other) → true or false

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

Source: show 

static VALUE
rb_hash_eql(hash1, hash2)
    VALUE hash1, hash2;
{
    return hash_equal(hash1, hash2, Qtrue);
}
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

Source: show 

static VALUE
rb_hash_fetch(argc, argv, hash)
    int argc;
    VALUE *argv;
    VALUE hash;
{
    VALUE key, if_none;
    VALUE val;
    long block_given;

    rb_scan_args(argc, argv, "11", &key, &if_none);

    block_given = rb_block_given_p();
    if (block_given && argc == 2) {
        rb_warn("block supersedes default value argument");
    }
    if (!st_lookup(RHASH(hash)->tbl, key, &val)) {
        if (block_given) return rb_yield(key);
        if (argc == 1) {
            rb_raise(rb_eIndexError, "key not found");
        }
        return if_none;
    }
    return val;
}
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

Source: show 

static VALUE
rb_hash_has_key(hash, key)
    VALUE hash;
    VALUE key;
{
    if (st_lookup(RHASH(hash)->tbl, key, 0)) {
        return Qtrue;
    }
    return Qfalse;
}
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

Source: show 

static VALUE
rb_hash_has_value(hash, val)
    VALUE hash;
    VALUE val;
{
    VALUE data[2];

    data[0] = Qfalse;
    data[1] = val;
    rb_hash_foreach(hash, rb_hash_search_value, (st_data_t)data);
    return data[0];
}
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?).

Source: show 

static VALUE
rb_hash_hash(hash)
    VALUE hash;
{
    return rb_exec_recursive(recursive_hash, hash, 0);
}
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

Source: show 

static VALUE
rb_hash_has_key(hash, key)
    VALUE hash;
    VALUE key;
{
    if (st_lookup(RHASH(hash)->tbl, key, 0)) {
        return Qtrue;
    }
    return Qfalse;
}
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

Source: show 

static VALUE
rb_hash_index(hash, value)
    VALUE hash, value;
{
    VALUE args[2];

    args[0] = value;
    args[1] = Qnil;

    rb_hash_foreach(hash, index_i, (st_data_t)args);

    return args[1];
}
hsh.indexes(key, ...) => array hsh.indices(key, ...) => array

Deprecated in favor of Hash#select.

Source: show 

static VALUE
rb_hash_indexes(argc, argv, hash)
    int argc;
    VALUE *argv;
    VALUE hash;
{
    VALUE indexes;
    int i;

    rb_warn("Hash#%s is deprecated; use Hash#values_at",
            rb_id2name(rb_frame_last_func()));
    indexes = rb_ary_new2(argc);
    for (i=0; i<argc; i++) {
        RARRAY(indexes)->ptr[i] = rb_hash_aref(hash, argv[i]);
        RARRAY(indexes)->len++;
    }
    return indexes;
}
hsh.indexes(key, ...) => array hsh.indices(key, ...) => array

Deprecated in favor of Hash#select.

Source: show 

static VALUE
rb_hash_indexes(argc, argv, hash)
    int argc;
    VALUE *argv;
    VALUE hash;
{
    VALUE indexes;
    int i;

    rb_warn("Hash#%s is deprecated; use Hash#values_at",
            rb_id2name(rb_frame_last_func()));
    indexes = rb_ary_new2(argc);
    for (i=0; i<argc; i++) {
        RARRAY(indexes)->ptr[i] = rb_hash_aref(hash, argv[i]);
        RARRAY(indexes)->len++;
    }
    return indexes;
}
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}

Source: show 

static VALUE
rb_hash_replace(hash, hash2)
    VALUE hash, hash2;
{
    hash2 = to_hash(hash2);
    if (hash == hash2) return hash;
    rb_hash_clear(hash);
    rb_hash_foreach(hash2, replace_i, hash);
    RHASH(hash)->ifnone = RHASH(hash2)->ifnone;
    if (FL_TEST(hash2, HASH_PROC_DEFAULT)) {
        FL_SET(hash, HASH_PROC_DEFAULT);
    }
    else {
        FL_UNSET(hash, HASH_PROC_DEFAULT);
    }

    return hash;
}
hsh.inspect => string

Return the contents of this hash as a string.

Source: show 

static VALUE
rb_hash_inspect(hash)
    VALUE hash;
{
    if (RHASH(hash)->tbl == 0 || RHASH(hash)->tbl->num_entries == 0)
        return rb_str_new2("{}");
    if (rb_inspecting_p(hash)) return rb_str_new2("{...}");
    return rb_protect_inspect(inspect_hash, hash, 0);
}
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"}

Source: show 

static VALUE
rb_hash_invert(hash)
    VALUE hash;
{
    VALUE h = rb_hash_new();

    rb_hash_foreach(hash, rb_hash_invert_i, h);
    return h;
}
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

Source: show 

static VALUE
rb_hash_has_key(hash, key)
    VALUE hash;
    VALUE key;
{
    if (st_lookup(RHASH(hash)->tbl, key, 0)) {
        return Qtrue;
    }
    return Qfalse;
}
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"]

Source: show 

static VALUE
rb_hash_keys(hash)
    VALUE hash;
{
    VALUE ary;

    ary = rb_ary_new();
    rb_hash_foreach(hash, keys_i, ary);

    return ary;
}
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

Source: show 

static VALUE
rb_hash_size(hash)
    VALUE hash;
{
    return INT2FIX(RHASH(hash)->tbl->num_entries);
}
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

Source: show 

static VALUE
rb_hash_has_key(hash, key)
    VALUE hash;
    VALUE key;
{
    if (st_lookup(RHASH(hash)->tbl, key, 0)) {
        return Qtrue;
    }
    return Qfalse;
}
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}

Source: show 

static VALUE
rb_hash_merge(hash1, hash2)
    VALUE hash1, hash2;
{
    return rb_hash_update(rb_obj_dup(hash1), hash2);
}
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}

Source: show 

static VALUE
rb_hash_update(hash1, hash2)
    VALUE hash1, hash2;
{
    hash2 = to_hash(hash2);
    if (rb_block_given_p()) {
        rb_hash_foreach(hash2, rb_hash_update_block_i, hash1);
    }
    else {
        rb_hash_foreach(hash2, rb_hash_update_i, hash1);
    }
    return hash1;
}
pretty_print(q)

Source: show 

     # File lib/pp.rb, line 315
315:   def pretty_print(q)
316:     q.pp_hash self
317:   end
pretty_print_cycle(q)

Source: show 

     # File lib/pp.rb, line 319
319:   def pretty_print_cycle(q)
320:     q.text(empty? ? '{}' : '{...}')
321:   end
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

Source: show 

static VALUE
rb_hash_rehash(hash)
    VALUE hash;
{
    st_table *tbl;

    rb_hash_modify(hash);
    tbl = st_init_table_with_size(&objhash, RHASH(hash)->tbl->num_entries);
    rb_hash_foreach(hash, rb_hash_rehash_i, (st_data_t)tbl);
    st_free_table(RHASH(hash)->tbl);
    RHASH(hash)->tbl = tbl;

    return hash;
}
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.

Source: show 

static VALUE
rb_hash_reject(hash)
    VALUE hash;
{
    return rb_hash_delete_if(rb_obj_dup(hash));
}
hsh.reject! {| key, value | block } → hsh or nil

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

Source: show 

VALUE
rb_hash_reject_bang(hash)
    VALUE hash;
{
    int n;

    RETURN_ENUMERATOR(hash, 0, 0);
    n = RHASH(hash)->tbl->num_entries;
    rb_hash_delete_if(hash);
    if (n == RHASH(hash)->tbl->num_entries) return Qnil;
    return hash;
}
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}

Source: show 

static VALUE
rb_hash_replace(hash, hash2)
    VALUE hash, hash2;
{
    hash2 = to_hash(hash2);
    if (hash == hash2) return hash;
    rb_hash_clear(hash);
    rb_hash_foreach(hash2, replace_i, hash);
    RHASH(hash)->ifnone = RHASH(hash2)->ifnone;
    if (FL_TEST(hash2, HASH_PROC_DEFAULT)) {
        FL_SET(hash, HASH_PROC_DEFAULT);
    }
    else {
        FL_UNSET(hash, HASH_PROC_DEFAULT);
    }

    return hash;
}
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]]

Source: show 

VALUE
rb_hash_select(hash)
    VALUE hash;
{
    VALUE result;

    RETURN_ENUMERATOR(hash, 0, 0);
    result = rb_ary_new();
    rb_hash_foreach(hash, select_i, result);
    return result;
}
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"}

Source: show 

static VALUE
rb_hash_shift(hash)
    VALUE hash;
{
    struct shift_var var;

    rb_hash_modify(hash);
    var.key = Qundef;
    if (RHASH(hash)->iter_lev > 0) {
        rb_hash_foreach(hash, shift_i_safe, (st_data_t)&var);
        if (var.key != Qundef) {
            st_data_t key = var.key;
            if (st_delete_safe(RHASH(hash)->tbl, &key, 0, Qundef)) {
                FL_SET(hash, HASH_DELETED);
            }
        }
    }
    else {
        rb_hash_foreach(hash, shift_i, (st_data_t)&var);
    }

    if (var.key != Qundef) {
        return rb_assoc_new(var.key, var.val);
    }
    else if (FL_TEST(hash, HASH_PROC_DEFAULT)) {
        return rb_funcall(RHASH(hash)->ifnone, id_call, 2, hash, Qnil);
    }
    else {
        return RHASH(hash)->ifnone;
    }
}
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

Source: show 

static VALUE
rb_hash_size(hash)
    VALUE hash;
{
    return INT2FIX(RHASH(hash)->tbl->num_entries);
}
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]]

Source: show 

static VALUE
rb_hash_sort(hash)
    VALUE hash;
{
    VALUE entries = rb_hash_to_a(hash);
    rb_ary_sort_bang(entries);
    return entries;
}
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}

Source: show 

VALUE
rb_hash_aset(hash, key, val)
    VALUE hash, key, val;
{
    rb_hash_modify(hash);
    if (TYPE(key) != T_STRING || st_lookup(RHASH(hash)->tbl, key, 0)) {
        st_insert(RHASH(hash)->tbl, key, val);
    }
    else {
        st_add_direct(RHASH(hash)->tbl, rb_str_new4(key), val);
    }
    return val;
}
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]]

Source: show 

static VALUE
rb_hash_to_a(hash)
    VALUE hash;
{
    VALUE ary;

    ary = rb_ary_new();
    rb_hash_foreach(hash, to_a_i, ary);
    if (OBJ_TAINTED(hash)) OBJ_TAINT(ary);

    return ary;
}
hsh.to_hash => hsh

Returns self.

Source: show 

static VALUE
rb_hash_to_hash(hash)
    VALUE hash;
{
    return hash;
}
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"

Source: show 

static VALUE
rb_hash_to_s(hash)
    VALUE hash;
{
    if (rb_inspecting_p(hash)) return rb_str_new2("{...}");
    return rb_protect_inspect(to_s_hash, hash, 0);
}
to_yaml( opts = {} )

Source: show 

    # File lib/yaml/rubytypes.rb, line 37
37:         def to_yaml( opts = {} )
38:                 YAML::quick_emit( self, opts ) do |out|
39:             out.map( taguri, to_yaml_style ) do |map|
40:                 each do |k, v|
41:                     map.add( k, v )
42:                 end
43:             end
44:         end
45:         end
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}

Source: show 

static VALUE
rb_hash_update(hash1, hash2)
    VALUE hash1, hash2;
{
    hash2 = to_hash(hash2);
    if (rb_block_given_p()) {
        rb_hash_foreach(hash2, rb_hash_update_block_i, hash1);
    }
    else {
        rb_hash_foreach(hash2, rb_hash_update_i, hash1);
    }
    return hash1;
}
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

Source: show 

static VALUE
rb_hash_has_value(hash, val)
    VALUE hash;
    VALUE val;
{
    VALUE data[2];

    data[0] = Qfalse;
    data[1] = val;
    rb_hash_foreach(hash, rb_hash_search_value, (st_data_t)data);
    return data[0];
}
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]

Source: show 

static VALUE
rb_hash_values(hash)
    VALUE hash;
{
    VALUE ary;

    ary = rb_ary_new();
    rb_hash_foreach(hash, values_i, ary);

    return ary;
}
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"]

Source: show 

VALUE
rb_hash_values_at(argc, argv, hash)
    int argc;
    VALUE *argv;
    VALUE hash;
{
    VALUE result = rb_ary_new();
    long i;

    for (i=0; i<argc; i++) {
        rb_ary_push(result, rb_hash_aref(hash, argv[i]));
    }
    return result;
}
yaml_initialize( tag, val )

Source: show 

    # File lib/yaml/rubytypes.rb, line 28
28:     def yaml_initialize( tag, val )
29:         if Array === val
30:             update Hash.[]( *val )              # Convert the map to a sequence
31:         elsif Hash === val
32:             update val
33:         else
34:             raise YAML::TypeError, "Invalid map explicitly tagged #{ tag }: " + val.inspect
35:         end
36:     end