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Dict implements a Key - Value dictionary.
The representation of a dictionary is not defined.
dictionary()
as returned by new/0
append(Key, Value, Dict1) -> Dict2
Types:
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
Types:
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.
Types:
Key = term()
Dict1 = Dict2 = dictionary()
This function erases all items with a given key from a dictionary.
Types:
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.
Types:
Dict = dictionary()
Keys = [term()]
This function returns a list of all keys in the dictionary.
Types:
Pred = fun(Key, Value) -> bool()
Key = Value = term()
Dict1 = Dict2 = dictionary()
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:
Key = Value = term()
Dict = dictionary()
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.
Types:
Fun = fun(Key, Value, AccIn) -> AccOut
Key = Value = term()
Acc0 = Acc1 = AccIn = AccOut = term()
Dict = dictionary()
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 list is empty. The evaluation order is
undefined.
Types:
List = [{Key, Value}]
Dict = dictionary()
This function converts the key/value list List to a
dictionary.
Types:
Key = term()
Dict = dictionary()
This function tests if Key is contained in
the dictionary Dict.
Types:
Fun = fun(Key, Value1) -> Value2
Key = Value1 = Value2 = term()
Dict1 = 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(Fun, Dict1, Dict2) -> Dict3
Types:
Fun = fun(Key, Value1, Value2) -> Value
Key = Value1 = Value2 = Value3 = term()
Dict1 = 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
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.
This function creates a new dictionary.
store(Key, Value, Dict1) -> Dict2
Types:
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.
Types:
Dict = dictionary()
List = [{Key, Value}]
This function converts the dictionary to a list representation.
update(Key, Fun, Dict1) -> Dict2
Types:
Key = term()
Fun = fun(Value1) -> Value2
Value1 = Value2 = term()
Dict1 = Dict2 = dictionary()
Update the 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:
Key = Initial = term()
Fun = fun(Value1) -> Value2
Value1 = Value2 = term()
Dict1 = Dict2 = dictionary()
Update the 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:
Key = term()
Increment = number()
Dict1 = Dict2 = 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 could be 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.