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NAME
dict - Key-Value Dictionary
DESCRIPTION
Dict implements a Key - Value dictionary. The representation of a dictionary is not
defined.
This module provides exactly the same interface as the module orddict. 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)
This function appends a new Value to the current list of values associated with
Key.
append_list(Key, ValList, Dict1) -> Dict2
Types:
Dict1 = Dict2 = dict(Key, Value)
ValList = [Value]
This function 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.
erase(Key, Dict1) -> Dict2
Types:
Dict1 = Dict2 = dict(Key, Value)
This function erases all items with a given key from a dictionary.
fetch(Key, Dict) -> Value
Types:
Dict = dict(Key, Value)
This function returns the value associated with Key in the dictionary Dict. fetch
assumes that the Key is present in the dictionary and an exception is generated if
Key is not in the dictionary.
fetch_keys(Dict) -> Keys
Types:
Dict = dict(Key, Value :: term())
Keys = [Key]
This function returns a list of all keys 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)
This function searches for a key in a dictionary. Returns {ok, Value} where Value
is the value associated with Key, or error if the key is not present in the
dictionary.
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 Dict together with an extra argument Acc
(short for accumulator). Fun must return a new accumulator which is passed to the
next call. Acc0 is returned if the dict is empty. The evaluation order is
undefined.
from_list(List) -> Dict
Types:
Dict = dict(Key, Value)
List = [{Key, Value}]
This function converts the Key - Value list List to a dictionary.
is_key(Key, Dict) -> boolean()
Types:
Dict = dict(Key, Value :: term())
This function tests if Key is contained in the dictionary Dict.
map(Fun, Dict1) -> Dict2
Types:
Fun = fun((Key, Value1) -> Value2)
Dict1 = dict(Key, Value1)
Dict2 = dict(Key, Value2)
map calls Fun on successive keys and values of 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)
merge 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 then Fun is called with the key and both values to
return a new value. merge could be defined as:
merge(Fun, D1, D2) ->
fold(fun (K, V1, D) ->
update(K, fun (V2) -> Fun(K, V1, V2) end, V1, D)
end, D2, D1).
but is faster.
new() -> dict()
This function creates a new dictionary.
size(Dict) -> integer() >= 0
Types:
Dict = dict()
Returns the number of elements in a Dict.
is_empty(Dict) -> boolean()
Types:
Dict = dict()
Returns true if Dict has no elements, false otherwise.
store(Key, Value, Dict1) -> Dict2
Types:
Dict1 = Dict2 = dict(Key, Value)
This function stores a Key - Value pair in a dictionary. If the Key already exists
in Dict1, the associated value is replaced by Value.
to_list(Dict) -> List
Types:
Dict = dict(Key, Value)
List = [{Key, Value}]
This function converts the dictionary to a list representation.
update(Key, Fun, Dict1) -> Dict2
Types:
Dict1 = Dict2 = dict(Key, Value)
Fun = fun((Value1 :: Value) -> Value2 :: Value)
Update 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
Update a value in a dictionary by calling Fun on the value to get a new value. If
Key is not present in the dictionary then Initial will be stored as the first
value. For example append/3 could 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()
Add Increment to the value associated with Key and store this value. If Key is not
present in the dictionary then Increment will be stored as the first value.
This could be defined as:
update_counter(Key, Incr, D) ->
update(Key, fun (Old) -> Old + Incr end, Incr, D).
but is faster.
NOTES
The functions append and append_list are included so we can store keyed values 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.
The function fetch should be used if the key is known to be in the dictionary, otherwise
find.
SEE ALSO
gb_trees(3erl), orddict(3erl)