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

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

Methods
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Included Modules
Class Public methods
Hash[ key, value, ... ] → new_hash Hash[ [ [key, value], ... ] ] → new_hash Hash[ object ] → new_hash

Creates a new hash populated with the given objects. Equivalent 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;
    int i;

    if (argc == 1) {
        tmp = rb_hash_s_try_convert(Qnil, argv[0]);
        if (!NIL_P(tmp)) {
            hash = hash_alloc(klass);
            if (RHASH(tmp)->ntbl) {
                RHASH(hash)->ntbl = st_copy(RHASH(tmp)->ntbl);
            }
            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 → new_hash Hash.new(obj) → new_hash 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 newused to create the hash. In the first form, the access returns nil. If objis 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()) {
        if (argc > 0) {
            rb_raise(rb_eArgError, "wrong number of arguments");
        }
        ifnone = rb_block_proc();
        default_proc_arity_check(ifnone);
        RHASH_IFNONE(hash) = ifnone;
        FL_SET(hash, HASH_PROC_DEFAULT);
    }
    else {
        rb_scan_args(argc, argv, "01", &ifnone);
        RHASH_IFNONE(hash) = ifnone;
    }

    return hash;
}
Hash.try_convert(obj) → hash or nil

Try to convert objinto a hash, using #to_hash method. Returns converted hash or nil if objcannot 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);
}
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
static VALUE
rb_hash_equal(VALUE hash1, VALUE hash2)
{
    return hash_equal(hash1, hash2, FALSE);
}
hsh[key] → value

Element Reference—Retrieves the valueobject corresponding to the keyobject. If not found, returns the default value (see Hash::newfor 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(hash)->ntbl || !st_lookup(RHASH(hash)->ntbl, key, &val)) {
        if (!FL_TEST(hash, HASH_PROC_DEFAULT) &&
            rb_method_basic_definition_p(CLASS_OF(hash), id_default)) {
            return RHASH_IFNONE(hash);
        }
        else {
            return rb_funcall(hash, id_default, 1, key);
        }
    }
    return (VALUE)val;
}
hsh[key] = value → value hsh.store(key, value) → value

Element Assignment—Associates the value given by valuewith the key given by key. keyshould not have its value changed while it is in use as a key (a Stringpassed 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}
VALUE
rb_hash_aset(VALUE hash, VALUE key, VALUE val)
{
    rb_hash_modify(hash);
    hash_update(hash, key);
    if (RHASH(hash)->ntbl->type == &identhash || rb_obj_class(key) != rb_cString) {
        st_insert(RHASH(hash)->ntbl, key, val);
    }
    else {
        st_insert2(RHASH(hash)->ntbl, key, val, copy_str_key);
    }
    return val;
}
hash.assoc(obj) → an_array or nil

Searches through the hash comparing objwith the key using ==. Returns the key-value pair (two elements array) or nilif 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 obj)
{
    VALUE args[2];

    args[0] = obj;
    args[1] = Qnil;
    rb_hash_foreach(hash, assoc_i, (VALUE)args);
    return args[1];
}
hsh.clear → hsh

Removes all key-value pairs from hsh.

h = { "a" => 100, "b" => 200 }   #=> {"a"=>100, "b"=>200}
h.clear                          #=> {}
static VALUE
rb_hash_clear(VALUE hash)
{
    rb_hash_modify_check(hash);
    if (!RHASH(hash)->ntbl)
        return hash;
    if (RHASH(hash)->ntbl->num_entries > 0) {
        if (RHASH(hash)->iter_lev > 0)
            rb_hash_foreach(hash, clear_i, 0);
        else
            st_clear(RHASH(hash)->ntbl);
    }

    return hash;
}
hsh.compare_by_identity → hsh

Makes hshcompare 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"]        #=> nil  # different objects.
h1[:c]         #=> "c"  # same symbols are all same.
static VALUE
rb_hash_compare_by_id(VALUE hash)
{
    rb_hash_modify(hash);
    RHASH(hash)->ntbl->type = &identhash;
    rb_hash_rehash(hash);
    return hash;
}
hsh.compare_by_identity? → true or false

Returns trueif hshwill compare its keys by their identity. Also see Hash#compare_by_identity.

static VALUE
rb_hash_compare_by_id_p(VALUE hash)
{
    if (!RHASH(hash)->ntbl)
        return Qfalse;
    if (RHASH(hash)->ntbl->type == &identhash) {
        return Qtrue;
    }
    return Qfalse;
}
hsh.default(key=nil) → obj

Returns the default value, the value that would be returned by hsh if keydid not exist in hsh. See also Hash::newand 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 key, ifnone;

    rb_scan_args(argc, argv, "01", &key);
    ifnone = RHASH_IFNONE(hash);
    if (FL_TEST(hash, HASH_PROC_DEFAULT)) {
        if (argc == 0) return Qnil;
        return rb_funcall(ifnone, id_yield, 2, hash, key);
    }
    return ifnone;
}
hsh.default = obj → obj

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 Procthat 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(hash);
    RHASH_IFNONE(hash) = ifnone;
    FL_UNSET(hash, HASH_PROC_DEFAULT);
    return ifnone;
}
hsh.default_proc → anObject

If Hash::newwas 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;
}
hsh.default_proc = proc_obj → proc_obj

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

h.default_proc = proc do |hash, key|
  hash[key] = key + key
end
h[2]       #=> 4
h["cat"]   #=> "catcat"
static VALUE
rb_hash_set_default_proc(VALUE hash, VALUE proc)
{
    VALUE b;

    rb_hash_modify(hash);
    b = rb_check_convert_type(proc, T_DATA, "Proc", "to_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;
    default_proc_arity_check(proc);
    RHASH_IFNONE(hash) = proc;
    FL_SET(hash, HASH_PROC_DEFAULT);
    return proc;
}
hsh.delete(key) → value hsh.delete(key) {| key | block } → value

Deletes and returns a key-value pair from hshwhose key is equal to key. If the key is not found, returns the default value . 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"
VALUE
rb_hash_delete(VALUE hash, VALUE 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 hsh.delete_if → an_enumerator

Deletes every key-value pair from hshfor 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_ENUMERATOR(hash, 0, 0);
    rb_hash_modify(hash);
    rb_hash_foreach(hash, delete_if_i, hash);
    return hash;
}
hsh.each {| key, value | block } → hsh hsh.each_pair {| key, value | block } → hsh hsh.each → an_enumerator hsh.each_pair → an_enumerator

Calls blockonce 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_ENUMERATOR(hash, 0, 0);
    rb_hash_foreach(hash, each_pair_i, 0);
    return hash;
}
hsh.each_key {| key | block } → hsh hsh.each_key → an_enumerator

Calls blockonce 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_ENUMERATOR(hash, 0, 0);
    rb_hash_foreach(hash, each_key_i, 0);
    return hash;
}
hsh.each {| key, value | block } → hsh hsh.each_pair {| key, value | block } → hsh hsh.each → an_enumerator hsh.each_pair → an_enumerator

Calls blockonce 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_ENUMERATOR(hash, 0, 0);
    rb_hash_foreach(hash, each_pair_i, 0);
    return hash;
}
hsh.each_value {| value | block } → hsh hsh.each_value → an_enumerator

Calls blockonce 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_ENUMERATOR(hash, 0, 0);
    rb_hash_foreach(hash, each_value_i, 0);
    return hash;
}
hsh.empty? → true or false

Returns trueif hshcontains no key-value pairs.

{}.empty?   #=> true
static VALUE
rb_hash_empty_p(VALUE hash)
{
    return RHASH_EMPTY_P(hash) ? Qtrue : Qfalse;
}
hash.eql?(other) → true or false

Returns trueif hashand otherare both hashes with the same content.

static VALUE
rb_hash_eql(VALUE hash1, VALUE hash2)
{
    return hash_equal(hash1, hash2, TRUE);
}
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 KeyErrorexception; if defaultis 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, if_none;
    st_data_t 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 (!RHASH(hash)->ntbl || !st_lookup(RHASH(hash)->ntbl, key, &val)) {
        if (block_given) return rb_yield(key);
        if (argc == 1) {
            volatile 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_raise(rb_eKeyError, "key not found: %s", RSTRING_PTR(desc));
        }
        return if_none;
    }
    return (VALUE)val;
}
hash.flatten → an_array hash.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 Array#flatten, this method does not flatten recursively by default. The optional levelargument 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, tmp;

    ary = rb_hash_to_a(hash);
    if (argc == 0) {
        argc = 1;
        tmp = INT2FIX(1);
        argv = &tmp;
    }
    rb_funcall2(ary, rb_intern("flatten!"), argc, argv);
    return ary;
}
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 trueif the given key is present in hsh.

h = { "a" => 100, "b" => 200 }
h.has_key?("a")   #=> true
h.has_key?("z")   #=> false
static VALUE
rb_hash_has_key(VALUE hash, VALUE key)
{
    if (!RHASH(hash)->ntbl)
        return Qfalse;
    if (st_lookup(RHASH(hash)->ntbl, key, 0)) {
        return Qtrue;
    }
    return Qfalse;
}
hsh.has_value?(value) → true or false hsh.value?(value) → true or false

Returns trueif 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
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];
}
hsh.hash → fixnum

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

static VALUE
rb_hash_hash(VALUE hash)
{
    return rb_exec_recursive_outer(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 trueif the given key is present in hsh.

h = { "a" => 100, "b" => 200 }
h.has_key?("a")   #=> true
h.has_key?("z")   #=> false
static VALUE
rb_hash_has_key(VALUE hash, VALUE key)
{
    if (!RHASH(hash)->ntbl)
        return Qfalse;
    if (st_lookup(RHASH(hash)->ntbl, key, 0)) {
        return Qtrue;
    }
    return Qfalse;
}
hsh.replace(other_hash) → hsh

Replaces the contents of hshwith 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);
    hash2 = to_hash(hash2);
    if (hash == hash2) return hash;
    rb_hash_clear(hash);
    if (RHASH(hash2)->ntbl) {
        rb_hash_tbl(hash);
        RHASH(hash)->ntbl->type = RHASH(hash2)->ntbl->type;
    }
    rb_hash_foreach(hash2, replace_i, hash);
    RHASH_IFNONE(hash) = RHASH_IFNONE(hash2);
    if (FL_TEST(hash2, HASH_PROC_DEFAULT)) {
        FL_SET(hash, HASH_PROC_DEFAULT);
    }
    else {
        FL_UNSET(hash, HASH_PROC_DEFAULT);
    }

    return hash;
}
hsh.to_s → string hsh.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}"
Also aliased as: to_s
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);
}
hsh.invert → new_hash

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=>"m", 200=>"d", 300=>"y"}
static VALUE
rb_hash_invert(VALUE hash)
{
    VALUE h = rb_hash_new();

    rb_hash_foreach(hash, rb_hash_invert_i, h);
    return h;
}
hsh.keep_if {| key, value | block } → hsh hsh.keep_if → an_enumerator

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

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

VALUE
rb_hash_keep_if(VALUE hash)
{
    RETURN_ENUMERATOR(hash, 0, 0);
    rb_hash_modify(hash);
    rb_hash_foreach(hash, keep_if_i, hash);
    return hash;
}
hsh.key(value) → key

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];
}
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 trueif the given key is present in hsh.

h = { "a" => 100, "b" => 200 }
h.has_key?("a")   #=> true
h.has_key?("z")   #=> false
static VALUE
rb_hash_has_key(VALUE hash, VALUE key)
{
    if (!RHASH(hash)->ntbl)
        return Qfalse;
    if (st_lookup(RHASH(hash)->ntbl, 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"]
static VALUE
rb_hash_keys(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
static VALUE
rb_hash_size(VALUE hash)
{
    if (!RHASH(hash)->ntbl)
        return INT2FIX(0);
    return INT2FIX(RHASH(hash)->ntbl->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 trueif the given key is present in hsh.

h = { "a" => 100, "b" => 200 }
h.has_key?("a")   #=> true
h.has_key?("z")   #=> false
static VALUE
rb_hash_has_key(VALUE hash, VALUE key)
{
    if (!RHASH(hash)->ntbl)
        return Qfalse;
    if (st_lookup(RHASH(hash)->ntbl, key, 0)) {
        return Qtrue;
    }
    return Qfalse;
}
hsh.merge(other_hash) → new_hash hsh.merge(other_hash){|key, oldval, newval| block} → new_hash

Returns a new hash containing the contents of other_hashand the contents of hsh. If no block is specified, the value for entries with duplicate keys will be that of other_hash. Otherwise the value for each duplicate key is determined by calling the block with the key, its value in hshand 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.merge(h2){|key, oldval, newval| newval - oldval}
               #=> {"a"=>100, "b"=>54,  "c"=>300}
h1             #=> {"a"=>100, "b"=>200}
static VALUE
rb_hash_merge(VALUE hash1, VALUE 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_hashto 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 hshand 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}
static VALUE
rb_hash_update(VALUE hash1, VALUE hash2)
{
    rb_hash_modify(hash1);
    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)
# File lib/pp.rb, line 350
def pretty_print(q)
  q.pp_hash self
end
pretty_print_cycle(q)
# File lib/pp.rb, line 354
def pretty_print_cycle(q)
  q.text(empty? ? '{}' : '{...}')
end
hash.rassoc(obj) → an_array or nil

Searches through the hash comparing objwith 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];
}
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#rehashis called while an iterator is traversing the hash, an RuntimeErrorwill 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
static VALUE
rb_hash_rehash(VALUE hash)
{
    st_table *tbl;

    if (RHASH(hash)->iter_lev > 0) {
        rb_raise(rb_eRuntimeError, "rehash during iteration");
    }
    rb_hash_modify_check(hash);
    if (!RHASH(hash)->ntbl)
        return hash;
    tbl = st_init_table_with_size(RHASH(hash)->ntbl->type, RHASH(hash)->ntbl->num_entries);
    rb_hash_foreach(hash, rb_hash_rehash_i, (VALUE)tbl);
    st_free_table(RHASH(hash)->ntbl);
    RHASH(hash)->ntbl = tbl;

    return hash;
}
hsh.reject {| key, value | block } → a_hash hsh.reject → an_enumerator

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

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

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

VALUE
rb_hash_reject_bang(VALUE hash)
{
    st_index_t n;

    RETURN_ENUMERATOR(hash, 0, 0);
    rb_hash_modify(hash);
    if (!RHASH(hash)->ntbl)
        return Qnil;
    n = RHASH(hash)->ntbl->num_entries;
    rb_hash_foreach(hash, delete_if_i, hash);
    if (n == RHASH(hash)->ntbl->num_entries) return Qnil;
    return hash;
}
hsh.replace(other_hash) → hsh

Replaces the contents of hshwith 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);
    hash2 = to_hash(hash2);
    if (hash == hash2) return hash;
    rb_hash_clear(hash);
    if (RHASH(hash2)->ntbl) {
        rb_hash_tbl(hash);
        RHASH(hash)->ntbl->type = RHASH(hash2)->ntbl->type;
    }
    rb_hash_foreach(hash2, replace_i, hash);
    RHASH_IFNONE(hash) = RHASH_IFNONE(hash2);
    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} → a_hash hsh.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}
VALUE
rb_hash_select(VALUE hash)
{
    VALUE result;

    RETURN_ENUMERATOR(hash, 0, 0);
    result = rb_hash_new();
    rb_hash_foreach(hash, select_i, result);
    return result;
}
hsh.select! {| key, value | block } → hsh or nil hsh.select! → an_enumerator

Equivalent to Hash#keep_if, but returns nilif no changes were made.

VALUE
rb_hash_select_bang(VALUE hash)
{
    st_index_t n;

    RETURN_ENUMERATOR(hash, 0, 0);
    rb_hash_modify(hash);
    if (!RHASH(hash)->ntbl)
        return Qnil;
    n = RHASH(hash)->ntbl->num_entries;
    rb_hash_foreach(hash, keep_if_i, hash);
    if (n == RHASH(hash)->ntbl->num_entries) return Qnil;
    return hash;
}
hsh.shift → anArray or obj

Removes a key-value pair from hshand 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(hash);
    var.key = Qundef;
    if (RHASH(hash)->iter_lev == 0) {
        if (st_shift(RHASH(hash)->ntbl, &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_key(hash, var.key);
            return rb_assoc_new(var.key, var.val);
        }
    }
    if (FL_TEST(hash, HASH_PROC_DEFAULT)) {
        return rb_funcall(RHASH_IFNONE(hash), id_yield, 2, hash, Qnil);
    }
    else {
        return RHASH_IFNONE(hash);
    }
}
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
static VALUE
rb_hash_size(VALUE hash)
{
    if (!RHASH(hash)->ntbl)
        return INT2FIX(0);
    return INT2FIX(RHASH(hash)->ntbl->num_entries);
}
hsh[key] = value → value hsh.store(key, value) → value

Element Assignment—Associates the value given by valuewith the key given by key. keyshould not have its value changed while it is in use as a key (a Stringpassed 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}
VALUE
rb_hash_aset(VALUE hash, VALUE key, VALUE val)
{
    rb_hash_modify(hash);
    hash_update(hash, key);
    if (RHASH(hash)->ntbl->type == &identhash || rb_obj_class(key) != rb_cString) {
        st_insert(RHASH(hash)->ntbl, key, val);
    }
    else {
        st_insert2(RHASH(hash)->ntbl, key, val, copy_str_key);
    }
    return val;
}
hsh.to_a → array

Converts hshto 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();
    rb_hash_foreach(hash, to_a_i, ary);
    OBJ_INFECT(ary, hash);

    return ary;
}
hsh.to_hash => hsh

Returns self.

static VALUE
rb_hash_to_hash(VALUE hash)
{
    return hash;
}
to_s()
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_hashto 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 hshand 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}
static VALUE
rb_hash_update(VALUE hash1, VALUE hash2)
{
    rb_hash_modify(hash1);
    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 trueif 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
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];
}
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]
static VALUE
rb_hash_values(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"]
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;
}