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

dict, gb_trees

Summary

Types

Dictionary as returned by new/0.

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

-type orddict() :: orddict(_, _).
-type orddict(Key, Value) :: [{Key, Value}].

Dictionary as returned by new/0.

Functions

Link to this function

append(Key, Value, Orddict1)

View Source
-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]
Link to this function

append_list(Key, ValList, Orddict1)

View Source
-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,[])
-spec fetch_keys(Orddict) -> Keys when Orddict :: orddict(Key, Value :: term()), Keys :: [Key].

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
Link to this function

fold(Fun, Acc0, Orddict)

View Source
-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.

Link to this function

is_empty(Orddict)

View Source (since OTP 17.0)
-spec is_empty(Orddict) -> boolean() when Orddict :: orddict().

Returns true if Orddict has no elements, otherwise false.

-spec is_key(Key, Orddict) -> boolean() when Orddict :: orddict(Key, Value :: term()).

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}]
Link to this function

merge(Fun, Orddict1, Orddict2)

View Source
-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}]
-spec new() -> orddict(none(), none()).

Creates a new dictionary.

-spec size(Orddict) -> non_neg_integer() when Orddict :: orddict().

Returns the number of elements in an Orddict.

Link to this function

store(Key, Value, Orddict1)

View Source
-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}]
Link to this function

take(Key, Orddict)

View Source (since OTP 20.0)
-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.

Link to this function

update(Key, Fun, Orddict1)

View Source
-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}]
Link to this function

update(Key, Fun, Initial, Orddict1)

View Source
-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}]
Link to this function

update_counter(Key, Increment, Orddict1)

View Source
-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).