dict(3erl)						     Erlang Module Definition							dict(3erl)

NAME

       dict - Key-Value Dictionary

DESCRIPTION

       Dict implements a Key - Value dictionary. The representation of a dictionary is not defined.

       This module provides exactly the same interface as the module orddict . One difference is that while this module considers two keys as dif-
       ferent if they do not match ( =:= ), orddict considers two keys as different if and only if they do not compare equal ( == ).

DATA TYPES

       dictionary()
	 as returned by new/0

EXPORTS

       append(Key, Value, Dict1) -> Dict2

	      Types  Key = Value = term()
		     Dict1 = Dict2 = 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, Dict1) -> Dict2

	      Types  ValList = [Value]
		     Key = Value = term()
		     Dict1 = Dict2 = 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, Dict1) -> Dict2

	      Types  Key = term()
		     Dict1 = Dict2 = dictionary()

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

       fetch(Key, Dict) -> Value

	      Types  Key = Value = term()
		     Dict = dictionary()

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

       fetch_keys(Dict) -> Keys

	      Types  Dict = dictionary()
		     Keys = [term()]

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

       filter(Pred, Dict1) -> Dict2

	      Types  Pred = fun(Key, Value) -> bool()
		     Key = Value = term()
		     Dict1 = Dict2 = dictionary()

	      Dict2 is a dictionary of all keys and values in Dict1 for which Pred(Key, Value) is true .

       find(Key, Dict) -> {ok, Value} | error

	      Types  Key = Value = term()
		     Dict = 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, Dict) -> Acc1

	      Types  Fun = fun(Key, Value, AccIn) -> AccOut
		     Key = Value = term()
		     Acc0 = Acc1 = AccIn = AccOut = term()
		     Dict = dictionary()

	      Calls Fun on successive keys and values of Dict 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) -> Dict

	      Types  List = [{Key, Value}]
		     Dict = dictionary()

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

       is_key(Key, Dict) -> bool()

	      Types  Key = term()
		     Dict = dictionary()

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

       map(Fun, Dict1) -> Dict2

	      Types  Fun = fun(Key, Value1) -> Value2
		     Key = Value1 = Value2 = term()
		     Dict1 = Dict2 = dictionary()

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

       merge(Fun, Dict1, Dict2) -> Dict3

	      Types  Fun = fun(Key, Value1, Value2) -> Value
		     Key = Value1 = Value2 = Value3 = term()
		     Dict1 = Dict2 = Dict3 = dictionary()

	      merge  merges  two  dictionaries, Dict1 and Dict2 , 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() -> dictionary()

	      This function creates a new dictionary.

       size(Dict) -> int()

	      Types  Dict = dictionary()

	      Returns the number of elements in a Dict .

       store(Key, Value, Dict1) -> Dict2

	      Types  Key = Value = term()
		     Dict1 = Dict2 = dictionary()

	      This  function  stores  a Key - Value pair in a dictionary. If the Key already exists in Dict1 , the associated value is replaced by
	      Value .

       to_list(Dict) -> List

	      Types  Dict = dictionary()
		     List = [{Key, Value}]

	      This function converts the dictionary to a list representation.

       update(Key, Fun, Dict1) -> Dict2

	      Types  Key = term()
		     Fun = fun(Value1) -> Value2
		     Value1 = Value2 = term()
		     Dict1 = Dict2 = 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, Dict1) -> Dict2

	      Types  Key = Initial = term()
		     Fun = fun(Value1) -> Value2
		     Value1 = Value2 = term()
		     Dict1 = Dict2 = 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, Dict1) -> Dict2

	      Types  Key = term()
		     Increment = number()
		     Dict1 = Dict2 = 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 = dict:new(),
	 D1 = dict:store(files, [], D0),
	 D2 = dict:append(files, f1, D1),
	 D3 = dict:append(files, f2, D2),
	 D4 = dict:append(files, f3, D3),
	 dict: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

       gb_trees(3erl) , orddict(3erl)

Ericsson AB							   stdlib 1.17.3							dict(3erl)