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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
       compare equal (==).

DATA TYPES

       orddict() = [{Key :: term(), Value :: term()}]

              As returned by new/0.

EXPORTS

       append(Key, Value, Orddict1) -> Orddict2

              Types:

                 Key = Value = term()
                 Orddict1 = Orddict2 = orddict()

              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:

                 Key = term()
                 ValList = [Value :: term()]
                 Orddict1 = Orddict2 = orddict()

              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 = orddict()

              This function erases all items with a given key from a dictionary.

       fetch(Key, Orddict) -> Value

              Types:

                 Key = Value = term()
                 Orddict = orddict()

              This function returns the value associated with  Key  in  the  dictionary  Orddict.
              fetch  assumes  that  the  Key  is  present  in  the dictionary and an exception is
              generated if Key is not in the dictionary.

       fetch_keys(Orddict) -> Keys

              Types:

                 Orddict = orddict()
                 Keys = [term()]

              This function returns a list of all keys in the dictionary.

       filter(Pred, Orddict1) -> Orddict2

              Types:

                 Pred = fun((Key :: term(), Value :: term()) -> boolean())
                 Orddict1 = Orddict2 = orddict()

              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 = term()
                 Orddict = orddict()
                 Value = term()

              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 :: term(), Value :: term(), AccIn :: term()) ->
                             AccOut :: term())
                 Acc0 = Acc1 = term()
                 Orddict = orddict()

              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 :: term(), Value :: term()}]
                 Orddict = orddict()

              This function converts the Key - Value list List to a dictionary.

       is_key(Key, Orddict) -> boolean()

              Types:

                 Key = term()
                 Orddict = orddict()

              This function tests if Key is contained in the dictionary Orddict.

       map(Fun, Orddict1) -> Orddict2

              Types:

                 Fun =
                     fun((Key :: term(), Value1 :: term()) -> Value2 :: term())
                 Orddict1 = Orddict2 = orddict()

              map calls Fun on successive keys and values of Orddict1 to return a new  value  for
              each key. The evaluation order is undefined.

       merge(Fun, Orddict1, Orddict2) -> Orddict3

              Types:

                 Fun =
                     fun((Key :: term(), Value1 :: term(), Value2 :: term()) ->
                             Value :: term())
                 Orddict1 = Orddict2 = Orddict3 = orddict()

              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() -> orddict()

              This function creates a new dictionary.

       size(Orddict) -> integer() >= 0

              Types:

                 Orddict = orddict()

              Returns the number of elements in an Orddict.

       store(Key, Value, Orddict1) -> Orddict2

              Types:

                 Key = Value = term()
                 Orddict1 = Orddict2 = orddict()

              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 = orddict()
                 List = [{Key :: term(), Value :: term()}]

              This function converts the dictionary to a list representation.

       update(Key, Fun, Orddict1) -> Orddict2

              Types:

                 Key = term()
                 Fun = fun((Value1 :: term()) -> Value2 :: term())
                 Orddict1 = Orddict2 = orddict()

              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 :: term()) -> Value2 :: term())
                 Orddict1 = Orddict2 = orddict()

              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 = orddict()

              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)