Hash

Class

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

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

A Hash 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 Hash can also be created through its ::new 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 Hash.new:

grades = Hash.new(0)

Or by using the default= method:

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

Accessing a value in a Hash 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 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

`Hash` 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 Object#eql?

Class Methods

Hash[ key, value, ... ] → new_hash

Hash[ [ [key, value], ... ] ] → new_hash

Hash[ object ] → new_hash

hash.c View on GitHub

          
            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 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);
    for (i=0; i<argc; i+=2) {
        rb_hash_aset(hash, argv[i], argv[i + 1]);
    }

    return 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}

Hash.new → new_hash

Hash.new(obj) → new_hash

Hash.new {|hash, key| block } → new_hash

hash.c View on GitHub

          
            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();
        default_proc_arity_check(ifnone);
        RHASH_SET_IFNONE(hash, ifnone);
        FL_SET(hash, HASH_PROC_DEFAULT);
    }
    else {
        rb_check_arity(argc, 0, 1);
        ifnone = argc == 0 ? Qnil : argv[0];
        RHASH_SET_IFNONE(hash, ifnone);
    }

    return 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"]

Hash.try_convert(obj) → hash or nil

hash.c View on GitHub

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

Try to convert obj into a hash, using to_hash 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

Instance Methods

hash < other → true or false

hash.c View on GitHub

          
            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);
}

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

hash <= other → true or false

hash.c View on GitHub

          
            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);
}

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

hsh == other_hash → true or false

hash.c View on GitHub

          
            static VALUE
rb_hash_equal(VALUE hash1, VALUE hash2)
{
    return hash_equal(hash1, hash2, 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

The orders of each hashes are not compared.

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

hash > other → true or false

hash.c View on GitHub

          
            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);
}

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

hash >= other → true or false

hash.c View on GitHub

          
            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);
}

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

hsh[key] → value

hash.c View on GitHub

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

    if (!RHASH(hash)->ntbl || !st_lookup(RHASH(hash)->ntbl, key, &val)) {
        return rb_hash_default_value(hash, key);
    }
    return (VALUE)val;
}

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

hsh[key] = value → value

hash.c View on GitHub

          
            VALUE
rb_hash_aset(VALUE hash, VALUE key, VALUE val)
{
    int iter_lev = RHASH_ITER_LEV(hash);
    st_table *tbl = RHASH(hash)->ntbl;

    rb_hash_modify(hash);
    if (!tbl) {
        if (iter_lev > 0) no_new_key();
        tbl = hash_tbl(hash);
    }
    if (tbl->type == &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;
}

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

hsh.any? [{ |(key, value)| block }] → true or false

hash.c View on GitHub

          
            static VALUE
rb_hash_any_p(VALUE hash)
{
    VALUE ret = Qfalse;

    if (RHASH_EMPTY_P(hash)) return Qfalse;
    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)&ret);
    else
        rb_hash_foreach(hash, any_p_i, (VALUE)&ret);
    return ret;
}

hash.assoc(obj) → an_array or nil

hash.c View on GitHub

          
            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;
    table = RHASH(hash)->ntbl;
    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];
}

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

hsh.clear → hsh

hash.c View on GitHub

          
            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_ITER_LEV(hash) > 0)
            rb_hash_foreach(hash, clear_i, 0);
        else
            st_clear(RHASH(hash)->ntbl);
    }

    return hash;
}

Removes all key-value pairs from hsh.

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

hsh.compare_by_identity → hsh

hash.c View on GitHub

          
            static VALUE
rb_hash_compare_by_id(VALUE hash)
{
    if (rb_hash_compare_by_id_p(hash)) return hash;
    rb_hash_modify(hash);
    RHASH(hash)->ntbl->type = &identhash;
    rb_hash_rehash(hash);
    return hash;
}

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.

hsh.compare_by_identity? → true or false

hash.c View on GitHub

          
            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;
}

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

hsh.default(key=nil) → obj

hash.c View on GitHub

          
            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;
}

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

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

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

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

hsh.default = obj → obj

hash.c View on GitHub

          
            static VALUE
rb_hash_set_default(VALUE hash, VALUE ifnone)
{
    rb_hash_modify_check(hash);
    RHASH_SET_IFNONE(hash, ifnone);
    FL_UNSET(hash, HASH_PROC_DEFAULT);
    return ifnone;
}

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>

hsh.default_proc → anObject

hash.c View on GitHub

          
            static VALUE
rb_hash_default_proc(VALUE hash)
{
    if (FL_TEST(hash, HASH_PROC_DEFAULT)) {
        return RHASH_IFNONE(hash);
    }
    return Qnil;
}

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

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

hsh.default_proc = proc_obj or nil

hash.c View on GitHub

          
            VALUE
rb_hash_set_default_proc(VALUE hash, VALUE proc)
{
    VALUE b;

    rb_hash_modify_check(hash);
    if (NIL_P(proc)) {
        FL_UNSET(hash, HASH_PROC_DEFAULT);
        RHASH_SET_IFNONE(hash, proc);
        return proc;
    }
    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_SET_IFNONE(hash, proc);
    FL_SET(hash, HASH_PROC_DEFAULT);
    return proc;
}

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"

hsh.delete(key) → value

hsh.delete(key) {| key | block } → value

hash.c View on GitHub

          
            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;
        }
    }
}

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"

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

hsh.delete_if → an_enumerator

hash.c View on GitHub

          
            VALUE
rb_hash_delete_if(VALUE hash)
{
    RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    rb_hash_modify_check(hash);
    if (RHASH(hash)->ntbl)
        rb_hash_foreach(hash, delete_if_i, hash);
    return hash;
}

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}

hsh.dig(key, ...) → object

hash.c View on GitHub

          
            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);
}

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: Fixnum does not have #dig method
g.dig(:foo, :bar)           #=> TypeError: no implicit conversion of Symbol into Integer

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

hsh.each → an_enumerator

hash.c View on GitHub

An alias for each_pair

hsh.each_key {| key | block } → hsh

hsh.each_key → an_enumerator

hash.c View on GitHub

          
            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;
}

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

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

hsh.each_pair → an_enumerator

hash.c View on GitHub

          
            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;
}

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

hsh.each_value {| value | block } → hsh

hsh.each_value → an_enumerator

hash.c View on GitHub

          
            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;
}

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

hsh.empty? → true or false

hash.c View on GitHub

          
            static VALUE
rb_hash_empty_p(VALUE hash)
{
    return RHASH_EMPTY_P(hash) ? Qtrue : Qfalse;
}

Returns true if hsh contains no key-value pairs.

{}.empty?   #=> true

hash.eql?(other) → true or false

hash.c View on GitHub

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

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

hsh.fetch(key [, default] ) → obj

hsh.fetch(key) {| key | block } → obj

hash.c View on GitHub

          
            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(hash)->ntbl || !st_lookup(RHASH(hash)->ntbl, key, &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_raise(rb_eKeyError, "key not found: %"PRIsVALUE, desc);
        }
        return argv[1];
    }
    return (VALUE)val;
}

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 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

hsh.fetch_values(key, ...) → array

hsh.fetch_values(key, ...) { |key| block } → array

hash.c View on GitHub

          
            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;
}

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"]

hash.flatten → an_array

hash.flatten(level) → an_array

hash.c View on GitHub

          
            static VALUE
rb_hash_flatten(int argc, VALUE *argv, VALUE hash)
{
    VALUE ary;

    if (argc) {
        int level = NUM2INT(*argv);
        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);
        if (level - 1 > 0) {
            *argv = INT2FIX(level - 1);
            rb_funcall2(ary, id_flatten_bang, argc, argv);
        }
        else if (level < 0) {
            rb_funcall2(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;
}

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 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"]

hsh.has_key?(key) → true or false

hash.c View on GitHub

An alias for include?

hsh.has_value?(value) → true or false

hash.c View on GitHub

          
            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];
}

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

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

hsh.hash → fixnum

hash.c View on GitHub

          
            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 INT2FIX(hval);
}

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

hsh.include?(key) → true or false

hash.c View on GitHub

          
            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;
}

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.

hsh.inspect → string

hash.c View on GitHub

          
            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);
}

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}"

hsh.invert → new_hash

hash.c View on GitHub

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

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

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"}

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

hsh.keep_if → an_enumerator

hash.c View on GitHub

          
            VALUE
rb_hash_keep_if(VALUE hash)
{
    RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    rb_hash_modify_check(hash);
    if (RHASH(hash)->ntbl)
        rb_hash_foreach(hash, keep_if_i, hash);
    return hash;
}

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

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

hsh.key(value) → key

hash.c View on GitHub

          
            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];
}

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

hsh.key?(key) → true or false

hash.c View on GitHub

An alias for include?

hsh.keys → array

hash.c View on GitHub

          
            VALUE
rb_hash_keys(VALUE hash)
{
    VALUE keys;
    st_index_t size = RHASH_SIZE(hash);

    keys = rb_ary_new_capa(size);
    if (size == 0) return keys;

    if (ST_DATA_COMPATIBLE_P(VALUE)) {
        st_table *table = RHASH(hash)->ntbl;

        rb_gc_writebarrier_remember(keys);
        RARRAY_PTR_USE(keys, ptr, {
            size = st_keys_check(table, ptr, size, Qundef);
        });
        rb_ary_set_len(keys, size);
    }
    else {
        rb_hash_foreach(hash, keys_i, keys);
    }

    return keys;
}

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

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

hsh.length → fixnum

hash.c View on GitHub

An alias for size

hsh.member?(key) → true or false

hash.c View on GitHub

An alias for include?

hsh.merge(other_hash) → new_hash

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

hash.c View on GitHub

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

Returns a new hash containing the contents of other_hash and 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 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.merge(h2){|key, oldval, newval| newval - oldval}
               #=> {"a"=>100, "b"=>54,  "c"=>300}
h1             #=> {"a"=>100, "b"=>200}

hsh.merge!(other_hash) → hsh

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

hash.c View on GitHub

An alias for update

hash.rassoc(obj) → an_array or nil

hash.c View on GitHub

          
            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];
}

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

hsh.rehash → hsh

hash.c View on GitHub

          
            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(hash)->ntbl)
        return hash;
    tmp = hash_alloc(0);
    tbl = st_init_table_with_size(RHASH(hash)->ntbl->type, RHASH(hash)->ntbl->num_entries);
    RHASH(tmp)->ntbl = tbl;

    rb_hash_foreach(hash, rb_hash_rehash_i, (VALUE)tbl);
    st_free_table(RHASH(hash)->ntbl);
    RHASH(hash)->ntbl = tbl;
    RHASH(tmp)->ntbl = 0;

    return hash;
}

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

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

hsh.reject → an_enumerator

hash.c View on GitHub

          
            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;
}

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}

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

hsh.reject! → an_enumerator

hash.c View on GitHub

          
            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(hash)->ntbl->num_entries) return Qnil;
    return hash;
}

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

hsh.replace(other_hash) → hsh

hash.c View on GitHub

          
            static VALUE
rb_hash_replace(VALUE hash, VALUE hash2)
{
    st_table *table2;

    rb_hash_modify_check(hash);
    if (hash == hash2) return hash;
    hash2 = to_hash(hash2);

    RHASH_SET_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);

    table2 = RHASH(hash2)->ntbl;

    rb_hash_clear(hash);
    if (table2) hash_tbl(hash)->type = table2->type;
    rb_hash_foreach(hash2, replace_i, hash);

    return hash;
}

Replaces the contents of hsh with the contents of other_hash.

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

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

hsh.select → an_enumerator

hash.c View on GitHub

          
            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;
}

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}

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

hsh.select! → an_enumerator

hash.c View on GitHub

          
            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);
    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;
}

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

hsh.shift → anArray or obj

hash.c View on GitHub

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

    rb_hash_modify_check(hash);
    if (RHASH(hash)->ntbl) {
        var.key = Qundef;
        if (RHASH_ITER_LEV(hash) == 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_entry(hash, var.key);
                return rb_assoc_new(var.key, var.val);
            }
        }
    }
    return rb_hash_default_value(hash, Qnil);
}

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

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

hsh.size → fixnum

hash.c View on GitHub

          
            VALUE
rb_hash_size(VALUE hash)
{
    return INT2FIX(RHASH_SIZE(hash));
}

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

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

hsh.store(key, value) → value

hash.c View on GitHub

An alias for []=

hsh.to_a → array

hash.c View on GitHub

          
            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;
}

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]]

hsh.to_h → hsh or new_hash

hash.c View on GitHub

          
            static VALUE
rb_hash_to_h(VALUE hash)
{
    if (rb_obj_class(hash) != rb_cHash) {
        VALUE ret = rb_hash_new();
        if (!RHASH_EMPTY_P(hash))
            RHASH(ret)->ntbl = st_copy(RHASH(hash)->ntbl);
        if (FL_TEST(hash, HASH_PROC_DEFAULT)) {
            FL_SET(ret, HASH_PROC_DEFAULT);
        }
        RHASH_SET_IFNONE(ret, RHASH_IFNONE(hash));
        return ret;
    }
    return hash;
}

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

hsh.to_hash => hsh

hash.c View on GitHub

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

Returns self.

to_proc

hash.c View on GitHub

          
            static VALUE
rb_hash_to_proc(VALUE hash)
{
    return rb_func_proc_new(hash_proc_call, hash);
}

No documentation available

hsh.to_s → string

hash.c View on GitHub

An alias for inspect

hsh.update(other_hash) → hsh

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

hash.c View on GitHub

          
            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;
}

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

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

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

hsh.value?(value) → true or false

hash.c View on GitHub

An alias for has_value?

hsh.values → array

hash.c View on GitHub

          
            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)) {
        st_table *table = RHASH(hash)->ntbl;

        rb_gc_writebarrier_remember(values);
        RARRAY_PTR_USE(values, ptr, {
            size = st_values_check(table, ptr, size, Qundef);
        });
        rb_ary_set_len(values, size);
    }
    else {
        rb_hash_foreach(hash, values_i, values);
    }

    return values;
}

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

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

hsh.values_at(key, ...) → array

hash.c View on GitHub

          
            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;
}

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"]

Hash

Common Uses

Hash Keys

Hash[ key, value, ... ] → new_hash

Hash[ [ [key, value], ... ] ] → new_hash

Hash[ object ] → new_hash

Hash.new → new_hash

Hash.new(obj) → new_hash

Hash.new {|hash, key| block } → new_hash

Hash.try_convert(obj) → hash or nil

hash < other → true or false

hash <= other → true or false

hsh == other_hash → true or false

hash > other → true or false

hash >= other → true or false

hsh[key] → value

hsh[key] = value → value

Element Assignment

hsh.any? [{ |(key, value)| block }] → true or false

hash.assoc(obj) → an_array or nil

hsh.clear → hsh

hsh.compare_by_identity → hsh

hsh.compare_by_identity? → true or false

hsh.default(key=nil) → obj

hsh.default = obj → obj

hsh.default_proc → anObject

hsh.default_proc = proc_obj or nil

hsh.delete(key) → value

hsh.delete(key) {| key | block } → value

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

hsh.delete_if → an_enumerator

hsh.dig(key, ...) → object

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

hsh.each → an_enumerator

hsh.each_key {| key | block } → hsh

hsh.each_key → an_enumerator

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

hsh.each_pair → an_enumerator

hsh.each_value {| value | block } → hsh

hsh.each_value → an_enumerator

hsh.empty? → true or false

hash.eql?(other) → true or false

hsh.fetch(key [, default] ) → obj

hsh.fetch(key) {| key | block } → obj

hsh.fetch_values(key, ...) → array

hsh.fetch_values(key, ...) { |key| block } → array

hash.flatten → an_array

hash.flatten(level) → an_array

hsh.has_key?(key) → true or false

hsh.has_value?(value) → true or false

hsh.hash → fixnum

hsh.include?(key) → true or false

hsh.inspect → string

hsh.invert → new_hash

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

hsh.keep_if → an_enumerator

hsh.key(value) → key

hsh.key?(key) → true or false

hsh.keys → array

hsh.length → fixnum

hsh.member?(key) → true or false

hsh.merge(other_hash) → new_hash

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

hsh.merge!(other_hash) → hsh

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

hash.rassoc(obj) → an_array or nil

hsh.rehash → hsh

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

hsh.reject → an_enumerator

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

hsh.reject! → an_enumerator

hsh.replace(other_hash) → hsh

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

hsh.select → an_enumerator

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

hsh.select! → an_enumerator

hsh.shift → anArray or obj

hsh.size → fixnum

hsh.store(key, value) → value

hsh.to_a → array

`Hash` Keys