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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 different 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 together 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 order 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 undefined.
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 dictionary. All the Key-
Value pairs from both dictionaries are included in the new dictionary. If a key
occurs in both dictionaries, 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 exists 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, Initial 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 dictionary, otherwise
function find.
SEE ALSO
gb_trees(3erl), orddict(3erl)