orddict

20002013 Ericsson AB. All Rights Reserved. The contents of this file are subject to the Erlang Public License, Version 1.1, (the "License"); you may not use this file except in compliance with the License. You should have received a copy of the Erlang Public License along with this software. If not, it can be retrieved online at http://www.erlang.org/. Software distributed under the License is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License for the specific language governing rights and limitations under the License. orddict Robert Virding nobody nobody no 2007-04-16 B orddict.sgml

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 (==).

As returned by new/0.

Append a value to keys in a 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 new values to keys in a 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 a key from a dictionary

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

Look-up values in a dictionary

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.

Return all keys in a dictionary

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

Choose elements which satisfy a predicate

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

Search for a key in a 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 a function over a 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.

Convert a list of pairs to a dictionary

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

Test if a key is in a dictionary

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

Map a function over a dictionary

map calls Fun on successive keys and values of Orddict1 to return a new value for each key. The evaluation order is undefined.

Merge two dictionaries

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.

Create a dictionary

This function creates a new dictionary.

Return the number of elements in an ordered dictionary

Returns the number of elements in an Orddict.

Store a value in a 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.

Convert a dictionary to a list of pairs

This function converts the dictionary to a list representation.

Update a value in a 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 a value in a 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).

Increment a value in a 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.