orddict(3erl) Erlang Module Definition orddict(3erl)
NAME
orddict - Key-Value Dictionary as Ordered List
DESCRIPTION
Orddict implements a Key - Value dictionary. An orddict is a representation of a dictionary, where a list of pairs is used to store the
keys and values. The list is ordered after the keys.
This module provides exactly the same interface as the module dict but with a defined representation. One difference is that while dict
considers two keys as different if they do not match ( =:= ), this module considers two keys as different if and only if they do not com-
pare equal ( == ).
DATA TYPES
ordered_dictionary()
as returned by new/0
EXPORTS
append(Key, Value, Orddict1) -> Orddict2
Types Key = Value = term()
Orddict1 = Orddict2 = ordered_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, Orddict1) -> Orddict2
Types ValList = [Value]
Key = Value = term()
Orddict1 = Orddict2 = ordered_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.
erase(Key, Orddict1) -> Orddict2
Types Key = term()
Orddict1 = Orddict2 = ordered_dictionary()
This function erases all items with a given key from a dictionary.
fetch(Key, Orddict) -> Value
Types Key = Value = term()
Orddict = ordered_dictionary()
This function returns the value associated with Key in the dictionary Orddict . fetch assumes that the Key is present in the dictio-
nary and an exception is generated if Key is not in the dictionary.
fetch_keys(Orddict) -> Keys
Types Orddict = ordered_dictionary()
Keys = [term()]
This function returns a list of all keys in the dictionary.
filter(Pred, Orddict1) -> Orddict2
Types Pred = fun(Key, Value) -> bool()
Key = Value = term()
Orddict1 = Orddict2 = ordered_dictionary()
Orddict2 is a dictionary of all keys and values in Orddict1 for which Pred(Key, Value) is true .
find(Key, Orddict) -> {ok, Value} | error
Types Key = Value = term()
Orddict = ordered_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.
fold(Fun, Acc0, Orddict) -> Acc1
Types Fun = fun(Key, Value, AccIn) -> AccOut
Key = Value = term()
Acc0 = Acc1 = AccIn = AccOut = term()
Orddict = ordered_dictionary()
Calls Fun on successive keys and values of Orddict 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.
from_list(List) -> Orddict
Types List = [{Key, Value}]
Orddict = ordered_dictionary()
This function converts the Key - Value list List to a dictionary.
is_key(Key, Orddict) -> bool()
Types Key = term()
Orddict = ordered_dictionary()
This function tests if Key is contained in the dictionary Orddict .
map(Fun, Orddict1) -> Orddict2
Types Fun = fun(Key, Value1) -> Value2
Key = Value1 = Value2 = term()
Orddict1 = Orddict2 = ordered_dictionary()
map calls Func on successive keys and values of Orddict to return a new value for each key. The evaluation order is undefined.
merge(Fun, Orddict1, Orddict2) -> Orddict3
Types Fun = fun(Key, Value1, Value2) -> Value
Key = Value1 = Value2 = Value3 = term()
Orddict1 = Orddict2 = Orddict3 = ordered_dictionary()
merge merges two dictionaries, Orddict1 and Orddict2 , 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() -> ordered_dictionary()
This function creates a new dictionary.
size(Orddict) -> int()
Types Orddict = ordered_dictionary()
Returns the number of elements in an Orddict .
store(Key, Value, Orddict1) -> Orddict2
Types Key = Value = term()
Orddict1 = Orddict2 = ordered_dictionary()
This function stores a Key - Value pair in a dictionary. If the Key already exists in Orddict1 , the associated value is replaced by
Value .
to_list(Orddict) -> List
Types Orddict = ordered_dictionary()
List = [{Key, Value}]
This function converts the dictionary to a list representation.
update(Key, Fun, Orddict1) -> Orddict2
Types Key = term()
Fun = fun(Value1) -> Value2
Value1 = Value2 = term()
Orddict1 = Orddict2 = ordered_dictionary()
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, Orddict1) -> Orddict2
Types Key = Initial = term()
Fun = fun(Value1) -> Value2
Value1 = Value2 = term()
Orddict1 = Orddict2 = ordered_dictionary()
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, Orddict1) -> Orddict2
Types Key = term()
Increment = number()
Orddict1 = Orddict2 = ordered_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.
NOTES
The functions append and append_list are included so we can store keyed values in a list accumulator . For example:
> D0 = orddict:new(),
D1 = orddict:store(files, [], D0),
D2 = orddict:append(files, f1, D1),
D3 = orddict:append(files, f2, D2),
D4 = orddict:append(files, f3, D3),
orddict: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
dict(3erl) , gb_trees(3erl)
Ericsson AB stdlib 1.17.3 orddict(3erl)