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)