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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 different if they do not match ( =:= ), ord-
       dict 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  asso-
	      ciated  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  dic-
	      tionary.

       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 unde-
	      fined.

       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)
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