orddict

Key-Value Dictionary as Ordered List

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 (==).

Types

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

Dictionary as returned by new/0.

orddict() = orddict(term(), term())

Functions

append(Key, Value, Orddict1) -> Orddict2

Orddict1 = Orddict2 = orddict(Key, Value)

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

ValList = [Value]
Orddict1 = Orddict2 = orddict(Key, Value)

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

Orddict1 = Orddict2 = orddict(Key, Value)

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

fetch(Key, Orddict) -> Value

Orddict = orddict(Key, Value)

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

Orddict = orddict(Key, Value :: term())
Keys = [Key]

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

filter(Pred, Orddict1) -> Orddict2

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

Orddict2 is a dictionary of all keys and values in Orddict1 for which Pred(Key, Value) is true.

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

Orddict = orddict(Key, Value)

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

Fun = fun((Key, Value, AccIn) -> AccOut)
Orddict = orddict(Key, Value)
Acc0 = Acc1 = AccIn = AccOut = Acc

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.

from_list(List) -> Orddict

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

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

is_key(Key, Orddict) -> boolean()

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

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

map(Fun, Orddict1) -> Orddict2

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

map calls Fun on successive keys and values of Orddict1 to return a new value for each key.

merge(Fun, Orddict1, Orddict2) -> Orddict3

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

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

Orddict = orddict()

Returns the number of elements in an Orddict.

is_empty(Orddict) -> boolean()

Orddict = orddict()

Returns true if Orddict has no elements, false otherwise.

store(Key, Value, Orddict1) -> Orddict2

Orddict1 = Orddict2 = orddict(Key, Value)

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

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

This function converts the dictionary to a list representation.

update(Key, Fun, Orddict1) -> Orddict2

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

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

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

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

Orddict1 = Orddict2 = orddict(Key, Value)
Increment = number()

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).