Dict implements a Key - Value dictionary.
The representation of a dictionary is not defined.
append(Key, Value, Dict1) -> Dict2
Key = Value = term()Dict1 = Dict2 = dictionary()This function appends a new Value 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.
append_list(Key, ValList, Dict1) -> Dict2
ValList = [Value]Key = Value = [term()]Dict1 = Dict2 = dictionary()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.
Key = term()Dict1 = Dict2 = dictionary()This function erases all items with a given key from a dictionary.
Key = Value = term()Dict = dictionary()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.
Dict = dictionary()Keys = [term()]This function returns a list of all keys in the dictionary.
Pred = fun(Key, Value) -> bool()Dict1 = Dict2 = dictionary()Dict2 is a dictionary of all keys and values in
Dict1 for which Pred(Key, Value) is
true.
Key = term()Dict = dictionary()Result = {ok, Value} | errorThis 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(Function, Acc0, Dict) -> Acc1
Function = fun(Key, Value, AccIn) -> AccOutAcc0 = Acc1 = AccIn = AccOut = term()Dict = dictionary()Calls Function on successive keys and values of
Dict together with an extra argument Acc
(short for accumulator). Function must return a new
accumulator which is passed to the next call. Acc0
is returned if the list is empty. The evaluation order is
undefined.
List = [{Key, Value}]Dict = dictionary()This function converts the dictionary to a list representation.
Key = term()Dict = dictionary()This function tests if Key is contained in the dictionary Dict
Func = fun(Key, Value) -> ValueDict1 = Dict2 = dictionary()map calls Func on successive keys and values
of Dict to return a new value for each key. The evaluation
order is undefined.
merge(Func, Dict1, Dict2) -> Dict3
Func = fun(Key, Value1, Value2) -> ValueDict1 = Dict2 = Dict3 = dictionary()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
Func 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.
This function creates a new dictionary.
store(Key, Value, Dict1) -> Dict2
Key = Value = term()Dict1 = Dict2 = dictionary()This function stores a Key - Value pair in a dictionary. If the
Key already exists in Dict1, the associated value
is replaced by Value.
Dict = dictionary()List = [{Key, Value}]This function converts the dictionary to a list representation.
update(Key, Function, Dict) -> Dict
Key = term()Function = fun(Value) -> ValueDict = dictionary()Update the a value in a dictionary by calling
Function on the value to get a new value. An exception
is generated if Key is not present in the dictionary.
update(Key, Function, Initial, Dict) -> Dict
Key = Initial = term()Function = fun(Value) -> ValueDict = dictionary()Update the a value in a dictionary by calling
Function 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
we could define append/3 as:
append(Key, Val, D) ->
update(Key, fun (Old) -> Old ++ [Val] end, [Val], D).
update_counter(Key, Increment, Dict) -> Dict
Key = term()Increment = number()Dict = dictionary()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 is could have been defined as:
update_counter(Key, Incr, D) ->
update(Key, fun (Old) -> Old + Incr end, Incr, D).but is faster.
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.