View Source orddict (stdlib v6.0)
Key-value dictionary as ordered list.
This module provides 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 in the
Erlang term order.
This module provides the same interface as the dict module 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 compare equal (==).
Notes
Functions append/3 and append_list/3 are
included so that keyed values can be stored 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.
Function fetch/2 is to be used if the key is known to be in the
dictionary, otherwise function find/2.
See Also
Summary
Functions
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.
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.
Erases all items with a specified key from a dictionary.
Returns the value associated with Key in dictionary Orddict. This function
assumes that the Key is present in the dictionary. An exception is generated
if Key is not in the dictionary.
Returns a list of all keys in a dictionary.
Orddict2 is a dictionary of all keys and values in Orddict1 for which
Pred(Key, Value) is true.
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.
Calls Fun on successive keys and values of Orddict 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 list is empty.
Converts the Key-Value list List to a dictionary.
Returns true if Orddict has no elements, otherwise false.
Tests if Key is contained in dictionary Orddict.
Calls Fun on successive keys and values of Orddict1 to return a new value
for each key.
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.
Creates a new dictionary.
Returns the number of elements in an Orddict.
Stores a Key-Value pair in a dictionary. If the Key already exists in
Orddict1, the associated value is replaced by Value.
This function returns value from dictionary and new dictionary without this
value. Returns error if the key is not present in the dictionary.
Converts a dictionary to a list representation.
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.
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.
Adds Increment to the value associated with Key and store this value. If
Key is not present in the dictionary, Increment is stored as the first
value.
Types
Functions
-spec append(Key, Value, Orddict1) -> Orddict2 when Orddict1 :: orddict(Key, Value), Orddict2 :: orddict(Key, Value).
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.
See also section Notes.
Example 1:
1> OrdDict1 = orddict:from_list([{x, []}]).
[{x,[]}]
2> OrdDict2 = orddict:append(x, 1, OrdDict1).
[{x,[1]}]
3> OrdDict3 = orddict:append(x, 2, OrdDict2).
[{x,[1,2]}]
4> orddict:append(y, 3, OrdDict3).
[{x,[1,2]},{y,[3]}]Example 2:
1> OrdDict1 = orddict:from_list([{a, no_list}]).
[{a,no_list}]
2> orddict:append(a, 1, OrdDict1).
** exception error: bad argument
in operator ++/2
called as no_list ++ [1]-spec append_list(Key, ValList, Orddict1) -> Orddict2 when ValList :: [Value], Orddict1 :: orddict(Key, Value), Orddict2 :: orddict(Key, 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.
Example:
1> OrdDict1 = orddict:from_list([{x, []}]).
[{x,[]}]
2> OrdDict2 = orddict:append_list(x, [1,2], OrdDict1).
[{x,[1,2]}]
3> OrdDict3 = orddict:append_list(y, [3,4], OrdDict2).
[{x,[1,2]},{y,[3,4]}]-spec erase(Key, Orddict1) -> Orddict2 when Orddict1 :: orddict(Key, Value), Orddict2 :: orddict(Key, Value).
Erases all items with a specified key from a dictionary.
Example:
1> OrdDict1 = orddict:from_list([{a, 1}, {b, 2}]).
[{a,1},{b,2}]
2> orddict:erase(a, OrdDict1).
[{b,2}]-spec fetch(Key, Orddict) -> Value when Orddict :: orddict(Key, Value).
Returns the value associated with Key in dictionary Orddict. This function
assumes that the Key is present in the dictionary. An exception is generated
if Key is not in the dictionary.
See also section Notes.
Example:
1> OrdDict1 = orddict:from_list([{a, 1}, {b, 2}]).
[{a,1},{b,2}]
2> orddict:fetch(a, OrdDict1).
1
3> orddict:fetch(missing, OrdDict1).
** exception error: no function clause matching orddict:fetch(missing,[])Returns a list of all keys in a dictionary.
Example:
1> OrdDict1 = orddict:from_list([{a, 1}, {b, 2}]).
[{a,1},{b,2}]
2> orddict:fetch_keys(OrdDict1).
[a,b]-spec filter(Pred, Orddict1) -> Orddict2 when Pred :: fun((Key, Value) -> boolean()), Orddict1 :: orddict(Key, Value), Orddict2 :: orddict(Key, Value).
Orddict2 is a dictionary of all keys and values in Orddict1 for which
Pred(Key, Value) is true.
Example:
1> OrdDict1 = orddict:from_list([{a, 1}, {b, 2}]).
[{a,1},{b,2}]
2> orddict:filter(fun (K, V) -> V > 1 end, OrdDict1).
[{b,2}]-spec find(Key, Orddict) -> {ok, Value} | error when Orddict :: orddict(Key, Value).
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.
See also section Notes.
Example:
1> OrdDict1 = orddict:from_list([{a, 1}, {b, 2}]).
[{a,1},{b,2}]
2> orddict:find(a, OrdDict1).
{ok,1}
3> orddict:find(c, OrdDict1).
error-spec fold(Fun, Acc0, Orddict) -> Acc1 when Fun :: fun((Key, Value, AccIn) -> AccOut), Orddict :: orddict(Key, Value), Acc0 :: Acc, Acc1 :: Acc, AccIn :: Acc, AccOut :: Acc.
Calls Fun on successive keys and values of Orddict 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 list is empty.
Example:
1> OrdDict1 = orddict:from_list([{a, 1}, {b, 2}]).
[{a,1},{b,2}]
2> orddict:fold(fun (K, V, Acc) -> [{K, V+100} | Acc] end, [], OrdDict1).
[{b,102},{a,101}]-spec from_list(List) -> Orddict when List :: [{Key, Value}], Orddict :: orddict(Key, Value).
Converts the Key-Value list List to a dictionary.
Returns true if Orddict has no elements, otherwise false.
Tests if Key is contained in dictionary Orddict.
-spec map(Fun, Orddict1) -> Orddict2 when Fun :: fun((Key, Value1) -> Value2), Orddict1 :: orddict(Key, Value1), Orddict2 :: orddict(Key, Value2).
Calls Fun on successive keys and values of Orddict1 to return a new value
for each key.
Example:
1> OrdDict1 = orddict:from_list([{a, 1}, {b, 2}]).
[{a,1},{b,2}]
2> orddict:map(fun (_K, V) -> V + 100 end, OrdDict1).
[{a,101},{b,102}]-spec merge(Fun, Orddict1, Orddict2) -> Orddict3 when Fun :: fun((Key, Value1, Value2) -> Value), Orddict1 :: orddict(Key, Value1), Orddict2 :: orddict(Key, Value2), Orddict3 :: orddict(Key, Value).
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, Fun is called with the key
and both values to return a new value.
merge/3 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).Example:
1> OrdDict1 = orddict:from_list([{a, 1}, {b, 2}]).
[{a,1},{b,2}]
2> OrdDict2 = orddict:from_list([{b, 7}, {c, 8}]).
[{b,7},{c,8}]
3> orddict:merge(fun (K, V1, V2) -> V1 * V2 end, OrdDict1, OrdDict2).
[{a, 1},{b, 14},{c,8}]Creates a new dictionary.
-spec size(Orddict) -> non_neg_integer() when Orddict :: orddict().
Returns the number of elements in an Orddict.
-spec store(Key, Value, Orddict1) -> Orddict2 when Orddict1 :: orddict(Key, Value), Orddict2 :: orddict(Key, Value).
Stores a Key-Value pair in a dictionary. If the Key already exists in
Orddict1, the associated value is replaced by Value.
Example:
1> OrdDict1 = orddict:from_list([{a, 1}, {b, 2}]).
[{a,1},{b,2}]
2> orddict:store(a, 99, OrdDict1).
[{a,99},{b,2}]
3> orddict:store(c, 100, OrdDict1).
[{a,1},{b,2},{c,100}]-spec take(Key, Orddict) -> {Value, Orddict1} | error when Orddict :: orddict(Key, Value), Orddict1 :: orddict(Key, Value), Key :: term(), Value :: term().
This function returns value from dictionary and new dictionary without this
value. Returns error if the key is not present in the dictionary.
Example:
1> OrdDict1 = orddict:from_list([{a, 1}, {b, 2}]).
[{a,1},{b,2}]
2> orddict:take(a, OrdDict1).
{1, [{b,2}]}
3> orddict:take(missing, OrdDict1).
error-spec to_list(Orddict) -> List when Orddict :: orddict(Key, Value), List :: [{Key, Value}].
Converts a dictionary to a list representation.
-spec update(Key, Fun, Orddict1) -> Orddict2 when Fun :: fun((Value1 :: Value) -> Value2 :: Value), Orddict1 :: orddict(Key, Value), Orddict2 :: orddict(Key, 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.
Example:
1> OrdDict1 = orddict:from_list([{a, 1}, {b, 2}]).
[{a,1},{b,2}]
2> orddict:update(a, fun (V) -> V1 + 100 end, OrdDict1).
[{a, 101}, {b, 102}]-spec update(Key, Fun, Initial, Orddict1) -> Orddict2 when Initial :: Value, Fun :: fun((Value1 :: Value) -> Value2 :: Value), Orddict1 :: orddict(Key, Value), Orddict2 :: orddict(Key, 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 follows:
append(Key, Val, D) ->
update(Key, fun (Old) -> Old ++ [Val] end, [Val], D).Example 1:
1> OrdDict1 = orddict:from_list([{a, 1}, {b, 2}]).
[{a,1},{b,2}]
2> orddict:update(c, fun (V) -> V1 + 100 end, 99, OrdDict1).
[{a,1},{b,2},{c,99}]Example 2:
1> OrdDict1 = orddict:from_list([{a, 1}, {b, 2}]).
[{a,1},{b,2}]
2> orddict:update(a, fun (V) -> V1 + 100 end, 99, OrdDict1).
[{a,101},{b,2}]-spec update_counter(Key, Increment, Orddict1) -> Orddict2 when Orddict1 :: orddict(Key, Value), Orddict2 :: orddict(Key, Value), Increment :: number().
Adds Increment to the value associated with Key and store 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).