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NAME

       dict - Key-value dictionary.

DESCRIPTION

       This  module  provides  a  Key-Value dictionary. The representation of a dictionary is not
       defined.

       This module provides the same interface as the orddict(3erl)  module.  One  difference  is
       that while this module considers two keys as different if they do not match (=:=), orddict
       considers two keys as different if and only if they do not compare equal (==).

DATA TYPES

       dict(Key, Value)

              Dictionary as returned by new/0.

       dict() = dict(term(), term())

EXPORTS

       append(Key, Value, Dict1) -> Dict2

              Types:

                 Dict1 = Dict2 = dict(Key, Value)

              Appends a new Value to the current list of values associated with Key.

              See also section Notes.

       append_list(Key, ValList, Dict1) -> Dict2

              Types:

                 Dict1 = Dict2 = dict(Key, Value)
                 ValList = [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.

       erase(Key, Dict1) -> Dict2

              Types:

                 Dict1 = Dict2 = dict(Key, Value)

              Erases all items with a given key from a dictionary.

       fetch(Key, Dict) -> Value

              Types:

                 Dict = dict(Key, Value)

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

              See also section Notes.

       fetch_keys(Dict) -> Keys

              Types:

                 Dict = dict(Key, Value :: term())
                 Keys = [Key]

              Returns a list of all keys in dictionary Dict.

       take(Key, Dict) -> {Value, Dict1} | error

              Types:

                 Dict = Dict1 = dict(Key, Value)
                 Key = Value = term()

              This function returns value from dictionary  and  a  new  dictionary  without  this
              value. Returns error if the key is not present in the dictionary.

       filter(Pred, Dict1) -> Dict2

              Types:

                 Pred = fun((Key, Value) -> boolean())
                 Dict1 = Dict2 = dict(Key, Value)

              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:

                 Dict = dict(Key, Value)

              Searches for a key in dictionary Dict. 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.

       fold(Fun, Acc0, Dict) -> Acc1

              Types:

                 Fun = fun((Key, Value, AccIn) -> AccOut)
                 Dict = dict(Key, Value)
                 Acc0 = Acc1 = AccIn = AccOut = Acc

              Calls  Fun  on successive keys and values of dictionary Dict 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  dictionary is empty. The
              evaluation order is undefined.

       from_list(List) -> Dict

              Types:

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

              Converts the Key-Value list List to dictionary Dict.

       is_empty(Dict) -> boolean()

              Types:

                 Dict = dict()

              Returns true if dictionary Dict has no elements, otherwise false.

       is_key(Key, Dict) -> boolean()

              Types:

                 Dict = dict(Key, Value :: term())

              Tests if Key is contained in dictionary Dict.

       map(Fun, Dict1) -> Dict2

              Types:

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

              Calls Fun on successive keys and values of dictionary Dict1 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)
                 Dict1 = dict(Key, Value1)
                 Dict2 = dict(Key, Value2)
                 Dict3 = dict(Key, Value)

              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, Fun is called with the key and both values to return a
              new value. merge 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).

       new() -> dict()

              Creates a new dictionary.

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

              Types:

                 Dict = dict()

              Returns the number of elements in dictionary Dict.

       store(Key, Value, Dict1) -> Dict2

              Types:

                 Dict1 = Dict2 = dict(Key, Value)

              Stores a Key-Value pair in dictionary Dict2. If Key already exists  in  Dict1,  the
              associated value is replaced by Value.

       to_list(Dict) -> List

              Types:

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

              Converts dictionary Dict to a list representation.

       update(Key, Fun, Dict1) -> Dict2

              Types:

                 Dict1 = Dict2 = dict(Key, Value)
                 Fun = fun((Value1 :: Value) -> Value2 :: 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.

       update(Key, Fun, Initial, Dict1) -> Dict2

              Types:

                 Dict1 = Dict2 = dict(Key, Value)
                 Fun = fun((Value1 :: Value) -> Value2 :: Value)
                 Initial = 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:

              append(Key, Val, D) ->
                  update(Key, fun (Old) -> Old ++ [Val] end, [Val], D).

       update_counter(Key, Increment, Dict1) -> Dict2

              Types:

                 Dict1 = Dict2 = dict(Key, Value)
                 Increment = number()

              Adds Increment to the value associated with Key and stores 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).

NOTES

       Functions append and append_list are included so that keyed values can be stored 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.

       Function  fetch  is  to  be  used  if  the key is known to be in the dictionary, otherwise
       function find.

SEE ALSO

       gb_trees(3erl), orddict(3erl)