class Hash(K, V)
Overview
A Hash
represents a collection of key-value mappings, similar to a dictionary.
Main operations are storing a key-value mapping (#[]=
) and
querying the value associated to a key (#[]
). Key-value mappings can also be
deleted (#delete
).
Keys are unique within a hash. When adding a key-value mapping with a key that
is already in use, the old value will be forgotten.
# Create a new Hash for mapping String to Int32
hash = Hash(String, Int32).new
hash["one"] = 1
hash["two"] = 2
hash["one"] # => 1
Hash literals
can also be used to create a Hash
:
{"one" => 1, "two" => 2}
Implementation is based on an open hash table.
Two objects refer to the same hash key when their hash value (Object#hash
)
is identical and both objects are equal to each other (Object#==
).
Enumeration follows the order that the corresponding keys were inserted.
NOTE When using mutable data types as keys, changing the value of a key after
it was inserted into the Hash
may lead to undefined behaviour. This can be
restored by re-indexing the hash with #rehash
.
Included Modules
Defined in:
hash.crjson/any.cr
json/to_json.cr
yaml/any.cr
yaml/to_yaml.cr
Constructors
-
.new(default_value : V, initial_capacity = nil)
Creates a new empty
Hash
where the default_value is returned if a key is missing. - .new(ctx : YAML::ParseContext, node : YAML::Nodes::Node)
-
.new(pull : JSON::PullParser)
Reads a Hash from the given pull parser.
-
.new
Creates a new empty
Hash
. -
.new(block : Hash(K, V), K -> V | Nil = nil, *, initial_capacity = nil)
Creates a new empty
Hash
with a block for handling missing keys. - .new(ctx : YAML::ParseContext, node : YAML::Nodes::Node, &)
-
.new(initial_capacity = nil, &block : Hash(K, V), K -> V)
Creates a new empty
Hash
with a block that handles missing keys.
Class Method Summary
-
.zip(ary1 : Array(K), ary2 : Array(V))
Zips two arrays into a
Hash
, taking keys from ary1 and values from ary2.
Instance Method Summary
-
#==(other : Hash) : Bool
Compares with other.
- #==(other : JSON::Any)
- #==(other : YAML::Any)
-
#[](key)
Returns the value for the key given by key.
-
#[]=(key : K, value : V) : V
Sets the value of key to the given value.
-
#[]?(key)
Returns the value for the key given by key.
-
#clear : self
Empties a
Hash
and returns it. -
#clone : Hash(K, V)
Similar to
#dup
, but duplicates the values as well. -
#compact
Returns new
Hash
withoutnil
values. -
#compact! : self
Removes all
nil
value fromself
. - #compare_by_identity : self
-
#compare_by_identity? : Bool
Returns
true
of this Hash is comparing keys byobject_id
. -
#delete(key) : V | Nil
Deletes the key-value pair and returns the value, otherwise returns
nil
. -
#delete(key, &)
Deletes the key-value pair and returns the value, else yields key with given block.
-
#dig(key : K, *subkeys)
Traverses the depth of a structure and returns the value, otherwise raises
KeyError
. -
#dig?(key : K, *subkeys)
Traverses the depth of a structure and returns the value.
-
#dup : Hash(K, V)
Duplicates a
Hash
. -
#each(& : Tuple(K, V) -> ) : Nil
Calls the given block for each key-value pair and passes in the key and the value.
-
#each
Returns an iterator over the hash entries.
-
#each_key(& : K -> )
Calls the given block for each key-value pair and passes in the key.
-
#each_key
Returns an iterator over the hash keys.
-
#each_value(& : V -> )
Calls the given block for each key-value pair and passes in the value.
-
#each_value
Returns an iterator over the hash values.
-
#empty? : Bool
Returns
true
when hash contains no key-value pairs. -
#fetch(key, default)
Returns the value for the key given by key, or when not found the value given by default.
-
#fetch(key, &)
Returns the value for the key given by key, or when not found calls the given block with the key.
-
#first_key : K
Returns the first key in the hash.
-
#first_key? : K | Nil
Returns the first key if it exists, or returns
nil
. -
#first_value : V
Returns the first value in the hash.
-
#first_value? : V | Nil
Returns the first value if it exists, or returns
nil
. -
#has_key?(key) : Bool
Returns
true
when key given by key exists, otherwisefalse
. -
#has_value?(val) : Bool
Returns
true
when value given by value exists, otherwisefalse
. - #hash(hasher)
-
#inspect(io : IO) : Nil
Appends a String representation of this object which includes its class name, its object address and the values of all instance variables.
-
#invert : Hash(V, K)
Inverts keys and values.
-
#key_for(value) : K
Returns a key with the given value, else raises
KeyError
. -
#key_for(value, &)
Returns a key with the given value, else yields value with the given block.
-
#key_for?(value) : K | Nil
Returns a key with the given value, else
nil
. -
#keys : Array(K)
Returns a new
Array
with all the keys. -
#last_key : K
Returns the last key in the hash.
-
#last_key? : K | Nil
Returns the last key if it exists, or returns
nil
. -
#last_value : V
Returns the last value in the hash.
-
#last_value? : V | Nil
Returns the last value if it exists, or returns
nil
. -
#merge(other : Hash(L, W)) : Hash(K | L, V | W) forall L, W
Returns a new
Hash
with the keys and values of this hash and other combined. - #merge(other : Hash(L, W), & : L, V, W -> V | W) : Hash(K | L, V | W) forall L, W
-
#merge!(other : Hash) : self
Similar to
#merge
, but the receiver is modified. -
#merge!(other : Hash, &) : self
Adds the contents of other to this hash.
- #pretty_print(pp) : Nil
-
#proper_subset_of?(other : Hash) : Bool
Returns
true
ifself
is a subset of other. -
#proper_superset_of?(other : Hash) : Bool
Returns
true
if other is a subset ofself
or equals toself
. -
#put(key : K, value : V, &)
Sets the value of key to the given value.
-
#put_if_absent(key : K, value : V) : V
Sets the value of key to the given value, unless a value for key already exists.
-
#put_if_absent(key : K, & : K -> V) : V
Sets the value of key to the value returned by the given block, unless a value for key already exists.
-
#rehash : Nil
Rebuilds the hash table based on the current keys.
-
#reject(& : K, V -> ) : Hash(K, V)
Returns a new hash consisting of entries for which the block is falsey.
-
#reject(*keys) : Hash(K, V)
Returns a new
Hash
without the given keys. -
#reject!(& : K, V -> _)
Equivalent to
Hash#reject
, but makes modification on the current object rather than returning a new one. -
#reject!(keys : Enumerable) : self
Removes a list of keys out of hash.
-
#reject!(*keys) : self
Removes a list of keys out of hash.
-
#select(& : K, V -> ) : Hash(K, V)
Returns a new hash consisting of entries for which the block is truthy.
-
#select(keys : Enumerable) : Hash(K, V)
Returns a new
Hash
with the given keys. -
#select(*keys) : Hash(K, V)
Returns a new
Hash
with the given keys. -
#select!(& : K, V -> ) : self
Equivalent to
Hash#select
but makes modification on the current object rather than returning a new one. -
#select!(keys : Indexable) : self
Removes every element except the given ones.
-
#select!(keys : Enumerable) : self
Removes every element except the given ones.
-
#select!(*keys) : self
Removes every element except the given ones.
-
#shift : Tuple(K, V)
Deletes and returns the first key-value pair in the hash, or raises
IndexError
if the hash is empty. -
#shift(&)
Deletes and returns the first key-value pair in the hash.
-
#shift? : Tuple(K, V) | Nil
Same as
#shift
, but returnsnil
if the hash is empty. -
#size : Int32
Returns the number of elements in this Hash.
-
#subset_of?(other : Hash) : Bool
Returns
true
ifself
is a subset of other or equals to other. -
#superset_of?(other : Hash) : Bool
Returns
true
if other is a subset ofself
. - #to_a : Array(Tuple(K, V))
-
#to_a(&block : Tuple(K, V) -> U) : Array(U) forall U
Returns an
Array
with the results of running block against tuples with key and values belonging to this Hash. -
#to_h : self
Returns
self
. -
#to_json(json : JSON::Builder) : Nil
Serializes this Hash into JSON.
-
#to_s(io : IO) : Nil
Converts to a
String
. - #to_yaml(yaml : YAML::Nodes::Builder) : Nil
-
#transform_keys(& : K, V -> K2) : Hash(K2, V) forall K2
Returns a new hash with all keys converted using the block operation.
-
#transform_values(& : V, K -> V2) : Hash(K, V2) forall V2
Returns a new hash with the results of running block once for every value.
-
#transform_values!(& : V, K -> V) : self
Destructively transforms all values using a block.
-
#update(key : K, & : V -> V) : V
Updates the current value of key with the value returned by the given block (the current value is used as input for the block).
-
#values : Array(V)
Returns only the values as an
Array
. -
#values_at(*keys : K)
Returns a tuple populated with the values of the given keys, with the same order.
Instance methods inherited from module Iterable({K, V})
chunk(reuse = false, &block : {K, V} -> U) forall U
chunk,
chunk_while(reuse : Bool | Array({K, V}) = false, &block : {K, V}, {K, V} -> B) forall B
chunk_while,
cycle(n)cycle cycle, each each, each_cons(count : Int, reuse = false) each_cons, each_cons_pair each_cons_pair, each_slice(count : Int, reuse = false) each_slice, each_step(n : Int)
each_step(n : Int, *, offset : Int) each_step, each_with_index(offset = 0) each_with_index, each_with_object(obj) each_with_object, slice_after(reuse : Bool | Array({K, V}) = false, &block : {K, V} -> B) forall B
slice_after(pattern, reuse : Bool | Array({K, V}) = false) slice_after, slice_before(reuse : Bool | Array({K, V}) = false, &block : {K, V} -> B) forall B
slice_before(pattern, reuse : Bool | Array({K, V}) = false) slice_before, slice_when(reuse : Bool | Array({K, V}) = false, &block : {K, V}, {K, V} -> B) forall B slice_when
Instance methods inherited from module Enumerable({K, V})
accumulate(initial : U) : Array(U) forall Uaccumulate : Array({K, V})
accumulate(initial : U, &block : U, {K, V} -> U) : Array(U) forall U
accumulate(&block : {K, V}, {K, V} -> {K, V}) : Array({K, V}) accumulate, all?(& : {K, V} -> ) : Bool
all?(pattern) : Bool
all? : Bool all?, any?(& : {K, V} -> ) : Bool
any?(pattern) : Bool
any? : Bool any?, chunks(&block : {K, V} -> U) forall U chunks, compact_map(& : {K, V} -> _) compact_map, count(& : {K, V} -> ) : Int32
count(item) : Int32 count, cycle(n, & : {K, V} -> ) : Nil
cycle(& : {K, V} -> ) : Nil cycle, each(& : {K, V} -> ) each, each_cons(count : Int, reuse = false, &) each_cons, each_cons_pair(& : {K, V}, {K, V} -> ) : Nil each_cons_pair, each_slice(count : Int, reuse = false, &) each_slice, each_step(n : Int, *, offset : Int = 0, & : {K, V} -> ) : Nil each_step, each_with_index(offset = 0, &) each_with_index, each_with_object(obj : U, & : {K, V}, U -> ) : U forall U each_with_object, empty? : Bool empty?, find(if_none = nil, & : {K, V} -> ) find, find!(& : {K, V} -> ) : {K, V} find!, first(&)
first(count : Int) : Array({K, V})
first : {K, V} first, first? : {K, V} | Nil first?, flat_map(& : {K, V} -> _) flat_map, group_by(& : {K, V} -> U) forall U group_by, in_groups_of(size : Int, filled_up_with : U = nil) forall U
in_groups_of(size : Int, filled_up_with : U = nil, reuse = false, &) forall U in_groups_of, in_slices_of(size : Int) : Array(Array({K, V})) in_slices_of, includes?(obj) : Bool includes?, index(& : {K, V} -> ) : Int32 | Nil
index(obj) : Int32 | Nil index, index!(& : {K, V} -> ) : Int32
index!(obj) : Int32 index!, index_by(& : {K, V} -> U) : Hash(U, {K, V}) forall U index_by, join(io : IO, separator = "") : Nil
join(separator, io : IO) : Nil
join(separator = "") : String
join(io : IO, separator = "", & : {K, V}, IO -> )
join(separator, io : IO, &)
join(separator = "", & : {K, V} -> ) join, map(& : {K, V} -> U) : Array(U) forall U map, map_with_index(offset = 0, & : {K, V}, Int32 -> U) : Array(U) forall U map_with_index, max(count : Int) : Array({K, V})
max : {K, V} max, max? : {K, V} | Nil max?, max_by(& : {K, V} -> U) : {K, V} forall U max_by, max_by?(& : {K, V} -> U) : {K, V} | Nil forall U max_by?, max_of(& : {K, V} -> U) : U forall U max_of, max_of?(& : {K, V} -> U) : U | Nil forall U max_of?, min(count : Int) : Array({K, V})
min : {K, V} min, min? : {K, V} | Nil min?, min_by(& : {K, V} -> U) : {K, V} forall U min_by, min_by?(& : {K, V} -> U) : {K, V} | Nil forall U min_by?, min_of(& : {K, V} -> U) : U forall U min_of, min_of?(& : {K, V} -> U) : U | Nil forall U min_of?, minmax : Tuple({K, V}, {K, V}) minmax, minmax? : Tuple({K, V} | Nil, {K, V} | Nil) minmax?, minmax_by(& : {K, V} -> U) : Tuple({K, V}, {K, V}) forall U minmax_by, minmax_by?(& : {K, V} -> U) : Tuple({K, V}, {K, V}) | Tuple(Nil, Nil) forall U minmax_by?, minmax_of(& : {K, V} -> U) : Tuple(U, U) forall U minmax_of, minmax_of?(& : {K, V} -> U) : Tuple(U, U) | Tuple(Nil, Nil) forall U minmax_of?, none?(& : {K, V} -> ) : Bool
none?(pattern) : Bool
none? : Bool none?, one?(& : {K, V} -> ) : Bool
one?(pattern) : Bool
one? : Bool one?, partition(& : {K, V} -> ) : Tuple(Array({K, V}), Array({K, V}))
partition(type : U.class) forall U partition, present? : Bool present?, product(initial : Number)
product
product(initial : Number, & : {K, V} -> )
product(& : {K, V} -> _) product, reduce(memo, &)
reduce(&) reduce, reduce?(&) reduce?, reject(& : {K, V} -> )
reject(type : U.class) forall U
reject(pattern) : Array({K, V}) reject, sample(n : Int, random : Random = Random::DEFAULT) : Array({K, V})
sample(random : Random = Random::DEFAULT) : {K, V} sample, select(& : {K, V} -> )
select(type : U.class) : Array(U) forall U
select(pattern) : Array({K, V}) select, size : Int32 size, skip(count : Int) skip, skip_while(& : {K, V} -> ) : Array({K, V}) skip_while, sum(initial)
sum
sum(initial, & : {K, V} -> )
sum(& : {K, V} -> ) sum, take_while(& : {K, V} -> ) : Array({K, V}) take_while, tally(hash)
tally : Hash({K, V}, Int32) tally, tally_by(hash, &)
tally_by(&block : {K, V} -> U) : Hash(U, Int32) forall U tally_by, to_a : Array({K, V})
to_a(& : {K, V} -> U) : Array(U) forall U to_a, to_h
to_h(& : {K, V} -> Tuple(K, V)) forall K, V to_h, to_set : Set({K, V})
to_set(&block : {K, V} -> U) : Set(U) forall U to_set, zip(*others : Indexable | Iterable | Iterator, &)
zip(*others : Indexable | Iterable | Iterator) zip, zip?(*others : Indexable | Iterable | Iterator, &)
zip?(*others : Indexable | Iterable | Iterator) zip?
Class methods inherited from module Enumerable({K, V})
element_type(x)
element_type
Instance methods inherited from class Reference
==(other : self)==(other : JSON::Any)
==(other : YAML::Any)
==(other) ==, dup dup, hash(hasher) hash, initialize initialize, inspect(io : IO) : Nil inspect, object_id : UInt64 object_id, pretty_print(pp) : Nil pretty_print, same?(other : Reference) : Bool
same?(other : Nil) same?, to_s(io : IO) : Nil to_s
Constructor methods inherited from class Reference
new
new,
unsafe_construct(address : Pointer, *args, **opts) : self
unsafe_construct
Class methods inherited from class Reference
pre_initialize(address : Pointer)
pre_initialize
Instance methods inherited from class Object
! : Bool
!,
!=(other)
!=,
!~(other)
!~,
==(other)
==,
===(other : JSON::Any)===(other : YAML::Any)
===(other) ===, =~(other) =~, as(type : Class) as, as?(type : Class) as?, class class, dup dup, hash(hasher)
hash hash, in?(collection : Object) : Bool
in?(*values : Object) : Bool in?, inspect(io : IO) : Nil
inspect : String inspect, is_a?(type : Class) : Bool is_a?, itself itself, nil? : Bool nil?, not_nil!(message)
not_nil! not_nil!, pretty_inspect(width = 79, newline = "\n", indent = 0) : String pretty_inspect, pretty_print(pp : PrettyPrint) : Nil pretty_print, responds_to?(name : Symbol) : Bool responds_to?, tap(&) tap, to_json(io : IO) : Nil
to_json : String to_json, to_pretty_json(indent : String = " ") : String
to_pretty_json(io : IO, indent : String = " ") : Nil to_pretty_json, to_s(io : IO) : Nil
to_s : String to_s, to_yaml(io : IO) : Nil
to_yaml : String to_yaml, try(&) try, unsafe_as(type : T.class) forall T unsafe_as
Class methods inherited from class Object
from_json(string_or_io, root : String)from_json(string_or_io) from_json, from_yaml(string_or_io : String | IO) from_yaml
Constructor Detail
Creates a new empty Hash
where the default_value is returned if a key is missing.
inventory = Hash(String, Int32).new(0)
inventory["socks"] = 3
inventory["pickles"] # => 0
WARNING When the default value gets returned on a missing key, it is not stored into the hash under that key. If you want that behaviour, please use the overload with a block.
WARNING The default value is returned as-is. It gets neither duplicated nor cloned. For types with reference semantics this means it will be exactly the same object every time.
hash = Hash(String, Array(Int32)).new([1])
hash["a"][0] = 2
hash["b"] # => [2]
.new(&block : (Hash(K, V), K -> V))
is an alternative with a block that can return a different default value for each invocation.
The initial_capacity is useful to avoid unnecessary reallocations of the internal buffer in case of growth. If the number of elements a hash will hold is known, the hash should be initialized with that capacity for improved performance. Otherwise, the default is 8. Inputs lower than 8 are ignored.
Reads a Hash from the given pull parser.
Keys are read by invoking from_json_object_key?
on this hash's
key type (K
), which must return a value of type K
or nil
.
If nil
is returned a JSON::ParseException
is raised.
Values are parsed using the regular .new(pull : JSON::PullParser)
method.
Creates a new empty Hash
with a block for handling missing keys.
proc = ->(hash : Hash(String, Int32), key : String) { hash[key] = key.size }
hash = Hash(String, Int32).new(proc)
hash.size # => 0
hash["foo"] # => 3
hash.size # => 1
hash["bar"] = 10
hash["bar"] # => 10
The initial_capacity is useful to avoid unnecessary reallocations of the internal buffer in case of growth. If the number of elements a hash will hold is known, the hash should be initialized with that capacity for improved performance. Otherwise, the default is 8. Inputs lower than 8 are ignored.
Creates a new empty Hash
with a block that handles missing keys.
inventory = Hash(String, Int32).new(0)
inventory["socks"] = 3
inventory["pickles"] # => 0
WARNING When the default block is invoked on a missing key, its return value is not implicitly stored into the hash under that key. If you want that behaviour, you need to put it explicitly:
hash = Hash(String, Int32).new do |hash, key|
hash[key] = key.size
end
hash.size # => 0
hash["foo"] # => 3
hash.size # => 1
hash["bar"] = 10
hash["bar"] # => 10
The initial_capacity is useful to avoid unnecessary reallocations of the internal buffer in case of growth. If the number of elements a hash will hold is known, the hash should be initialized with that capacity for improved performance. Otherwise, the default is 8. Inputs lower than 8 are ignored.
Class Method Detail
Zips two arrays into a Hash
, taking keys from ary1 and values from ary2.
Hash.zip(["key1", "key2", "key3"], ["value1", "value2", "value3"])
# => {"key1" => "value1", "key2" => "value2", "key3" => "value3"}
Instance Method Detail
Compares with other. Returns true
if all key-value pairs are the same.
Returns the value for the key given by key.
If not found, returns the default value given by Hash.new
, otherwise raises KeyError
.
h = {"foo" => "bar"}
h["foo"] # => "bar"
h = Hash(String, String).new("bar")
h["foo"] # => "bar"
h = Hash(String, String).new { "bar" }
h["foo"] # => "bar"
h = Hash(String, String).new
h["foo"] # raises KeyError
Sets the value of key to the given value.
h = {} of String => String
h["foo"] = "bar"
h["foo"] # => "bar"
Returns the value for the key given by key.
If not found, returns nil
. This ignores the default value set by Hash.new
.
h = {"foo" => "bar"}
h["foo"]? # => "bar"
h["bar"]? # => nil
h = Hash(String, String).new("bar")
h["foo"]? # => nil
Similar to #dup
, but duplicates the values as well.
hash_a = {"foobar" => {"foo" => "bar"}}
hash_b = hash_a.clone
hash_b["foobar"]["foo"] = "baz"
hash_a # => {"foobar" => {"foo" => "bar"}}
Returns new Hash
without nil
values.
hash = {"hello" => "world", "foo" => nil}
hash.compact # => {"hello" => "world"}
Removes all nil
value from self
. Returns self
.
hash = {"hello" => "world", "foo" => nil}
hash.compact! # => {"hello" => "world"}
Makes this hash compare keys using their object identity (object_id)
for types that define such method (Reference
types, but also structs that
might wrap other Reference
types and delegate the object_id
method to them).
h1 = {"foo" => 1, "bar" => 2}
h1["fo" + "o"]? # => 1
h1.compare_by_identity
h1.compare_by_identity? # => true
h1["fo" + "o"]? # => nil # not the same String instance
Returns true
of this Hash is comparing keys by object_id
.
See #compare_by_identity
.
Deletes the key-value pair and returns the value, otherwise returns nil
.
h = {"foo" => "bar"}
h.delete("foo") # => "bar"
h.fetch("foo", nil) # => nil
Deletes the key-value pair and returns the value, else yields key with given block.
h = {"foo" => "bar"}
h.delete("foo") { |key| "#{key} not found" } # => "bar"
h.fetch("foo", nil) # => nil
h.delete("baz") { |key| "#{key} not found" } # => "baz not found"
Traverses the depth of a structure and returns the value, otherwise
raises KeyError
.
h = {"a" => {"b" => [10, 20, 30]}}
h.dig "a", "b" # => [10, 20, 30]
h.dig "a", "x" # raises KeyError
Traverses the depth of a structure and returns the value.
Returns nil
if not found.
h = {"a" => {"b" => [10, 20, 30]}}
h.dig? "a", "b" # => [10, 20, 30]
h.dig? "a", "x" # => nil
Duplicates a Hash
.
hash_a = {"foo" => "bar"}
hash_b = hash_a.dup
hash_b.merge!({"baz" => "qux"})
hash_a # => {"foo" => "bar"}
Calls the given block for each key-value pair and passes in the key and the value.
h = {"foo" => "bar"}
h.each do |key, value|
key # => "foo"
value # => "bar"
end
h.each do |key_and_value|
key_and_value # => {"foo", "bar"}
end
The enumeration follows the order the keys were inserted.
Returns an iterator over the hash entries.
Which behaves like an Iterator
returning a Tuple
consisting of the key and value types.
hsh = {"foo" => "bar", "baz" => "qux"}
iterator = hsh.each
iterator.next # => {"foo", "bar"}
iterator.next # => {"baz", "qux"}
The enumeration follows the order the keys were inserted.
Calls the given block for each key-value pair and passes in the key.
h = {"foo" => "bar"}
h.each_key do |key|
key # => "foo"
end
The enumeration follows the order the keys were inserted.
Returns an iterator over the hash keys.
Which behaves like an Iterator
consisting of the key's types.
hsh = {"foo" => "bar", "baz" => "qux"}
iterator = hsh.each_key
key = iterator.next
key # => "foo"
key = iterator.next
key # => "baz"
The enumeration follows the order the keys were inserted.
Calls the given block for each key-value pair and passes in the value.
h = {"foo" => "bar"}
h.each_value do |value|
value # => "bar"
end
The enumeration follows the order the keys were inserted.
Returns an iterator over the hash values.
Which behaves like an Iterator
consisting of the value's types.
hsh = {"foo" => "bar", "baz" => "qux"}
iterator = hsh.each_value
value = iterator.next
value # => "bar"
value = iterator.next
value # => "qux"
The enumeration follows the order the keys were inserted.
Returns true
when hash contains no key-value pairs.
h = Hash(String, String).new
h.empty? # => true
h = {"foo" => "bar"}
h.empty? # => false
Returns the value for the key given by key, or when not found the value given by default.
This ignores the default value set by Hash.new
.
h = {"foo" => "bar"}
h.fetch("foo", "foo") # => "bar"
h.fetch("bar", "foo") # => "foo"
Returns the value for the key given by key, or when not found calls the given block with the key.
h = {"foo" => "bar"}
h.fetch("foo") { "default value" } # => "bar"
h.fetch("bar") { "default value" } # => "default value"
h.fetch("bar") { |key| key.upcase } # => "BAR"
Returns the first key if it exists, or returns nil
.
hash = {"foo1" => "bar1", "foz2" => "baz2"}
hash.first_key? # => "foo1"
hash.clear
hash.first_key? # => nil
Returns the first value if it exists, or returns nil
.
hash = {"foo1" => "bar1", "foz2" => "baz2"}
hash.first_value? # => "bar1"
hash.clear
hash.first_value? # => nil
Returns true
when key given by key exists, otherwise false
.
h = {"foo" => "bar"}
h.has_key?("foo") # => true
h.has_key?("bar") # => false
Returns true
when value given by value exists, otherwise false
.
h = {"foo" => "bar"}
h.has_value?("foo") # => false
h.has_value?("bar") # => true
Appends a String representation of this object which includes its class name, its object address and the values of all instance variables.
class Person
def initialize(@name : String, @age : Int32)
end
end
Person.new("John", 32).inspect # => #<Person:0x10fd31f20 @name="John", @age=32>
Inverts keys and values. If there are duplicated values, the last key becomes the new value.
{"foo" => "bar"}.invert # => {"bar" => "foo"}
{"foo" => "bar", "baz" => "bar"}.invert # => {"bar" => "baz"}
Returns a key with the given value, else raises KeyError
.
hash = {"foo" => "bar", "baz" => "qux"}
hash.key_for("bar") # => "foo"
hash.key_for("qux") # => "baz"
hash.key_for("foobar") # raises KeyError (Missing hash key for value: foobar)
Returns a key with the given value, else yields value with the given block.
hash = {"foo" => "bar"}
hash.key_for("bar") { |value| value.upcase } # => "foo"
hash.key_for("qux") { |value| value.upcase } # => "QUX"
Returns a key with the given value, else nil
.
hash = {"foo" => "bar", "baz" => "qux"}
hash.key_for?("bar") # => "foo"
hash.key_for?("qux") # => "baz"
hash.key_for?("foobar") # => nil
Returns a new Array
with all the keys.
h = {"foo" => "bar", "baz" => "bar"}
h.keys # => ["foo", "baz"]
Returns the last key if it exists, or returns nil
.
hash = {"foo1" => "bar1", "foz2" => "baz2"}
hash.last_key? # => "foz2"
hash.clear
hash.last_key? # => nil
Returns the last value if it exists, or returns nil
.
hash = {"foo1" => "bar1", "foz2" => "baz2"}
hash.last_value? # => "baz2"
hash.clear
hash.last_value? # => nil
Returns a new Hash
with the keys and values of this hash and other combined.
A value in other takes precedence over the one in this hash.
hash = {"foo" => "bar"}
hash.merge({"baz" => "qux"})
# => {"foo" => "bar", "baz" => "qux"}
hash
# => {"foo" => "bar"}
Similar to #merge
, but the receiver is modified.
hash = {"foo" => "bar"}
hash.merge!({"baz" => "qux"})
hash # => {"foo" => "bar", "baz" => "qux"}
Adds the contents of other to this hash.
If a key exists in both hashes, the given block is called to determine the value to be used.
The block arguments are the key, the value in self
and the value in other.
hash = {"a" => 100, "b" => 200}
other = {"b" => 254, "c" => 300}
hash.merge!(other) { |key, v1, v2| v1 + v2 }
hash # => {"a" => 100, "b" => 454, "c" => 300}
Returns true
if self
is a subset of other.
Returns true
if other is a subset of self
or equals to self
.
Sets the value of key to the given value.
If a value already exists for key, that (old) value is returned. Otherwise the given block is invoked with key and its value is returned.
h = {} of Int32 => String
h.put(1, "one") { "didn't exist" } # => "didn't exist"
h.put(1, "uno") { "didn't exist" } # => "one"
h.put(2, "two") { |key| key.to_s } # => "2"
h # => {1 => "one", 2 => "two"}
Sets the value of key to the given value, unless a value for key already exists.
If a value already exists for key, that (old) value is returned. Otherwise value is returned.
h = {} of Int32 => String
h.put_if_absent(1, "one") # => "one"
h.put_if_absent(1, "uno") # => "one"
h.put_if_absent(2, "two") # => "two"
h # => {1 => "one", 2 => "two"}
Sets the value of key to the value returned by the given block, unless a value for key already exists.
If a value already exists for key, that (old) value is returned. Otherwise the given block is invoked with key and its value is returned.
h = {} of Int32 => Array(String)
h.put_if_absent(1) { |key| [key.to_s] } # => ["1"]
h.put_if_absent(1) { [] of String } # => ["1"]
h.put_if_absent(2) { |key| [key.to_s] } # => ["2"]
h # => {1 => ["1"], 2 => ["2"]}
hash.put_if_absent(key) { value }
is a more performant alternative to
hash[key] ||= value
that also works correctly when the hash may contain
falsey values.
Rebuilds the hash table based on the current keys.
When using mutable data types as keys, modifying a key after it was inserted
into the Hash
may lead to undefined behaviour. This method re-indexes the
hash using the current keys.
Returns a new hash consisting of entries for which the block is falsey.
h = {"a" => 100, "b" => 200, "c" => 300}
h.reject { |k, v| k > "a" } # => {"a" => 100}
h.reject { |k, v| v < 200 } # => {"b" => 200, "c" => 300}
Returns a new Hash
without the given keys.
{"a" => 1, "b" => 2, "c" => 3, "d" => 4}.reject("a", "c") # => {"b" => 2, "d" => 4}
Equivalent to Hash#reject
, but makes modification on the current object rather than returning a new one. Returns self
.
Removes a list of keys out of hash.
hash = {"a" => 1, "b" => 2, "c" => 3, "d" => 4}
hash.reject!(["a", "c"]) # => {"b" => 2, "d" => 4}
hash # => {"b" => 2, "d" => 4}
Removes a list of keys out of hash.
hash = {"a" => 1, "b" => 2, "c" => 3, "d" => 4}
hash.reject!("a", "c") # => {"b" => 2, "d" => 4}
hash # => {"b" => 2, "d" => 4}
Returns a new hash consisting of entries for which the block is truthy.
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}
Returns a new Hash
with the given keys.
{"a" => 1, "b" => 2, "c" => 3, "d" => 4}.select({"a", "c"}) # => {"a" => 1, "c" => 3}
{"a" => 1, "b" => 2, "c" => 3, "d" => 4}.select("a", "c") # => {"a" => 1, "c" => 3}
{"a" => 1, "b" => 2, "c" => 3, "d" => 4}.select(["a", "c"]) # => {"a" => 1, "c" => 3}
{"a" => 1, "b" => 2, "c" => 3, "d" => 4}.select(Set{"a", "c"}) # => {"a" => 1, "c" => 3}
Returns a new Hash
with the given keys.
{"a" => 1, "b" => 2, "c" => 3, "d" => 4}.select({"a", "c"}) # => {"a" => 1, "c" => 3}
{"a" => 1, "b" => 2, "c" => 3, "d" => 4}.select("a", "c") # => {"a" => 1, "c" => 3}
{"a" => 1, "b" => 2, "c" => 3, "d" => 4}.select(["a", "c"]) # => {"a" => 1, "c" => 3}
{"a" => 1, "b" => 2, "c" => 3, "d" => 4}.select(Set{"a", "c"}) # => {"a" => 1, "c" => 3}
Equivalent to Hash#select
but makes modification on the current object rather than returning a new one. Returns self
.
Removes every element except the given ones.
h1 = {"a" => 1, "b" => 2, "c" => 3, "d" => 4}.select!({"a", "c"})
h2 = {"a" => 1, "b" => 2, "c" => 3, "d" => 4}.select!("a", "c")
h3 = {"a" => 1, "b" => 2, "c" => 3, "d" => 4}.select!(["a", "c"])
h4 = {"a" => 1, "b" => 2, "c" => 3, "d" => 4}.select!(Set{"a", "c"})
h1 == h2 == h3 == h4 # => true
h1 # => {"a" => 1, "c" => 3}
Removes every element except the given ones.
h1 = {"a" => 1, "b" => 2, "c" => 3, "d" => 4}.select!({"a", "c"})
h2 = {"a" => 1, "b" => 2, "c" => 3, "d" => 4}.select!("a", "c")
h3 = {"a" => 1, "b" => 2, "c" => 3, "d" => 4}.select!(["a", "c"])
h4 = {"a" => 1, "b" => 2, "c" => 3, "d" => 4}.select!(Set{"a", "c"})
h1 == h2 == h3 == h4 # => true
h1 # => {"a" => 1, "c" => 3}
Removes every element except the given ones.
h1 = {"a" => 1, "b" => 2, "c" => 3, "d" => 4}.select!({"a", "c"})
h2 = {"a" => 1, "b" => 2, "c" => 3, "d" => 4}.select!("a", "c")
h3 = {"a" => 1, "b" => 2, "c" => 3, "d" => 4}.select!(["a", "c"])
h4 = {"a" => 1, "b" => 2, "c" => 3, "d" => 4}.select!(Set{"a", "c"})
h1 == h2 == h3 == h4 # => true
h1 # => {"a" => 1, "c" => 3}
Deletes and returns the first key-value pair in the hash,
or raises IndexError
if the hash is empty.
hash = {"foo" => "bar", "baz" => "qux"}
hash.shift # => {"foo", "bar"}
hash # => {"baz" => "qux"}
hash = {} of String => String
hash.shift # raises IndexError
Deletes and returns the first key-value pair in the hash. Yields to the given block if the hash is empty.
hash = {"foo" => "bar", "baz" => "qux"}
hash.shift { true } # => {"foo", "bar"}
hash # => {"baz" => "qux"}
hash = {} of String => String
hash.shift { true } # => true
hash # => {}
Same as #shift
, but returns nil
if the hash is empty.
hash = {"foo" => "bar", "baz" => "qux"}
hash.shift? # => {"foo", "bar"}
hash # => {"baz" => "qux"}
hash = {} of String => String
hash.shift? # => nil
Returns true
if self
is a subset of other or equals to other.
Returns an Array
of Tuple(K, V)
with key and values belonging to this Hash.
h = {1 => 'a', 2 => 'b', 3 => 'c'}
h.to_a # => [{1, 'a'}, {2, 'b'}, {3, 'c'}]
The order of the array follows the order the keys were inserted in the Hash.
Returns an Array
with the results of running block against tuples with key and values
belonging to this Hash.
h = {"first_name" => "foo", "last_name" => "bar"}
h.to_a { |_k, v| v.capitalize } # => ["Foo", "Bar"]
The order of the array follows the order the keys were inserted in the Hash.
Serializes this Hash into JSON.
Keys are serialized by invoking to_json_object_key
on them.
Values are serialized with the usual #to_json(json : JSON::Builder)
method.
Converts to a String
.
h = {"foo" => "bar"}
h.to_s # => "{\"foo\" => \"bar\"}"
h.to_s.class # => String
Returns a new hash with all keys converted using the block operation. The block can change a type of keys. The block yields the key and value.
hash = {:a => 1, :b => 2, :c => 3}
hash.transform_keys { |key| key.to_s } # => {"a" => 1, "b" => 2, "c" => 3}
hash.transform_keys { |key, value| key.to_s * value } # => {"a" => 1, "bb" => 2, "ccc" => 3}
Returns a new hash with the results of running block once for every value. The block can change a type of values. The block yields the value and key.
hash = {:a => 1, :b => 2, :c => 3}
hash.transform_values { |value| value + 1 } # => {:a => 2, :b => 3, :c => 4}
hash.transform_values { |value, key| "#{key}#{value}" } # => {:a => "a1", :b => "b2", :c => "c3"}
Destructively transforms all values using a block. Same as transform_values but modifies in place. The block cannot change a type of values. The block yields the value and key.
hash = {:a => 1, :b => 2, :c => 3}
hash.transform_values! { |value| value + 1 }
hash # => {:a => 2, :b => 3, :c => 4}
hash.transform_values! { |value, key| value + key.to_s[0].ord }
hash # => {:a => 99, :b => 101, :c => 103}
See #update
for updating a single value.
Updates the current value of key with the value returned by the given block (the current value is used as input for the block).
If no entry for key is present, but there's a default value (or default block) then that default value is used as input for the given block.
If no entry for key is present and the hash has no default value, it raises KeyError
.
It returns the value used as input for the given block (ie. the old value if key present, or the default value)
h = {"a" => 0, "b" => 1}
h.update("b") { |v| v + 41 } # => 1
h["b"] # => 42
h = Hash(String, Int32).new(40)
h.update("foo") { |v| v + 2 } # => 40
h["foo"] # => 42
h = {} of String => Int32
h.update("a") { 42 } # raises KeyError
See #transform_values!
for updating all the values.
Returns only the values as an Array
.
h = {"foo" => "bar", "baz" => "qux"}
h.values # => ["bar", "qux"]
Returns a tuple populated with the values of the given keys, with the same order. Raises if a key is not found.
{"a" => 1, "b" => 2, "c" => 3, "d" => 4}.values_at("a", "c") # => {1, 3}