dict(3erl) Erlang Module Definition dict(3erl)
NAME
dict - Key-value dictionary.
DESCRIPTION
This module provides a Key-Value dictionary. The representation of a
dictionary is not defined.
This module provides the same interface as the orddict(3erl) module.
One difference is that while this module considers two keys as differ-
ent if they do not match (=:=), orddict considers two keys as different
if and only if they do not compare equal (==).
DATA TYPES
dict(Key, Value)
Dictionary as returned by new/0.
dict() = dict(term(), term())
EXPORTS
append(Key, Value, Dict1) -> Dict2
Types:
Dict1 = Dict2 = dict(Key, Value)
Appends a new Value to the current list of values associated
with Key.
See also section Notes.
append_list(Key, ValList, Dict1) -> Dict2
Types:
Dict1 = Dict2 = dict(Key, Value)
ValList = [Value]
Appends a list of values ValList to the current list of values
associated with Key. An exception is generated if the initial
value associated with Key is not a list of values.
See also section Notes.
erase(Key, Dict1) -> Dict2
Types:
Dict1 = Dict2 = dict(Key, Value)
Erases all items with a given key from a dictionary.
fetch(Key, Dict) -> Value
Types:
Dict = dict(Key, Value)
Returns the value associated with Key in dictionary Dict. This
function assumes that Key is present in dictionary Dict, and an
exception is generated if Key is not in the dictionary.
See also section Notes.
fetch_keys(Dict) -> Keys
Types:
Dict = dict(Key, Value :: term())
Keys = [Key]
Returns a list of all keys in dictionary Dict.
take(Key, Dict) -> {Value, Dict1} | error
Types:
Dict = Dict1 = dict(Key, Value)
Key = Value = term()
This function returns value from dictionary and a new dictionary
without this value. Returns error if the key is not present in
the dictionary.
filter(Pred, Dict1) -> Dict2
Types:
Pred = fun((Key, Value) -> boolean())
Dict1 = Dict2 = dict(Key, Value)
Dict2 is a dictionary of all keys and values in Dict1 for which
Pred(Key, Value) is true.
find(Key, Dict) -> {ok, Value} | error
Types:
Dict = dict(Key, Value)
Searches for a key in dictionary Dict. Returns {ok, Value},
where Value is the value associated with Key, or error if the
key is not present in the dictionary.
See also section Notes.
fold(Fun, Acc0, Dict) -> Acc1
Types:
Fun = fun((Key, Value, AccIn) -> AccOut)
Dict = dict(Key, Value)
Acc0 = Acc1 = AccIn = AccOut = Acc
Calls Fun on successive keys and values of dictionary Dict to-
gether with an extra argument Acc (short for accumulator). Fun
must return a new accumulator that is passed to the next call.
Acc0 is returned if the dictionary is empty. The evaluation or-
der is undefined.
from_list(List) -> Dict
Types:
Dict = dict(Key, Value)
List = [{Key, Value}]
Converts the Key-Value list List to dictionary Dict.
is_empty(Dict) -> boolean()
Types:
Dict = dict()
Returns true if dictionary Dict has no elements, otherwise
false.
is_key(Key, Dict) -> boolean()
Types:
Dict = dict(Key, Value :: term())
Tests if Key is contained in dictionary Dict.
map(Fun, Dict1) -> Dict2
Types:
Fun = fun((Key, Value1) -> Value2)
Dict1 = dict(Key, Value1)
Dict2 = dict(Key, Value2)
Calls Fun on successive keys and values of dictionary Dict1 to
return a new value for each key. The evaluation order is unde-
fined.
merge(Fun, Dict1, Dict2) -> Dict3
Types:
Fun = fun((Key, Value1, Value2) -> Value)
Dict1 = dict(Key, Value1)
Dict2 = dict(Key, Value2)
Dict3 = dict(Key, Value)
Merges two dictionaries, Dict1 and Dict2, to create a new dic-
tionary. All the Key-Value pairs from both dictionaries are in-
cluded in the new dictionary. If a key occurs in both dictionar-
ies, Fun is called with the key and both values to return a new
value. merge can be defined as follows, but is faster:
merge(Fun, D1, D2) ->
fold(fun (K, V1, D) ->
update(K, fun (V2) -> Fun(K, V1, V2) end, V1, D)
end, D2, D1).
new() -> dict()
Creates a new dictionary.
size(Dict) -> integer() >= 0
Types:
Dict = dict()
Returns the number of elements in dictionary Dict.
store(Key, Value, Dict1) -> Dict2
Types:
Dict1 = Dict2 = dict(Key, Value)
Stores a Key-Value pair in dictionary Dict2. If Key already ex-
ists in Dict1, the associated value is replaced by Value.
to_list(Dict) -> List
Types:
Dict = dict(Key, Value)
List = [{Key, Value}]
Converts dictionary Dict to a list representation.
update(Key, Fun, Dict1) -> Dict2
Types:
Dict1 = Dict2 = dict(Key, Value)
Fun = fun((Value1 :: Value) -> Value2 :: Value)
Updates a value in a dictionary by calling Fun on the value to
get a new value. An exception is generated if Key is not present
in the dictionary.
update(Key, Fun, Initial, Dict1) -> Dict2
Types:
Dict1 = Dict2 = dict(Key, Value)
Fun = fun((Value1 :: Value) -> Value2 :: Value)
Initial = Value
Updates a value in a dictionary by calling Fun on the value to
get a new value. If Key is not present in the dictionary, Ini-
tial is stored as the first value. For example, append/3 can be
defined as:
append(Key, Val, D) ->
update(Key, fun (Old) -> Old ++ [Val] end, [Val], D).
update_counter(Key, Increment, Dict1) -> Dict2
Types:
Dict1 = Dict2 = dict(Key, Value)
Increment = number()
Adds Increment to the value associated with Key and stores this
value. If Key is not present in the dictionary, Increment is
stored as the first value.
This can be defined as follows, but is faster:
update_counter(Key, Incr, D) ->
update(Key, fun (Old) -> Old + Incr end, Incr, D).
NOTES
Functions append and append_list are included so that keyed values can
be stored in a list accumulator, for example:
> D0 = dict:new(),
D1 = dict:store(files, [], D0),
D2 = dict:append(files, f1, D1),
D3 = dict:append(files, f2, D2),
D4 = dict:append(files, f3, D3),
dict:fetch(files, D4).
[f1,f2,f3]
This saves the trouble of first fetching a keyed value, appending a new
value to the list of stored values, and storing the result.
Function fetch is to be used if the key is known to be in the dictio-
nary, otherwise function find.
SEE ALSO
gb_trees(3erl), orddict(3erl)
Ericsson AB stdlib 3.13 dict(3erl)