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<?xml version="1.0" encoding="latin1" ?>
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<!DOCTYPE erlref SYSTEM "erlref.dtd">
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<holder>Ericsson AB, All Rights Reserved</holder>
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The contents of this file are subject to the Erlang Public License,
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Version 1.1, (the "License"); you may not use this file except in
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compliance with the License. You should have received a copy of the
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Erlang Public License along with this software. If not, it can be
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retrieved online at http://www.erlang.org/.
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Software distributed under the License is distributed on an "AS IS"
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basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
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the License for the specific language governing rights and limitations
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The Initial Developer of the Original Code is Ericsson AB.
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<title>orddict</title>
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<prepared>Robert Virding</prepared>
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<responsible>nobody</responsible>
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<approved>nobody</approved>
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<date>2007-04-16</date>
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<file>orddict.sgml</file>
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<module>orddict</module>
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<modulesummary>Key-Value Dictionary as Ordered List</modulesummary>
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<p><c>Orddict</c> implements a <c>Key</c> - <c>Value</c> dictionary.
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An <c>orddict</c> is a representation of a dictionary, where a
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list of pairs is used to store the keys and values. The list is
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ordered after the keys.</p>
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<p>This module provides exactly the same interface as the module
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<c>dict</c> but with a defined representation. One difference is
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that while <c>dict</c> considers two keys as different if they
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do not match (<c>=:=</c>), this module considers two keys as
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different if and only if they do not compare equal
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<title>DATA TYPES</title>
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as returned by new/0</code>
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<name>append(Key, Value, Orddict1) -> Orddict2</name>
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<fsummary>Append a value to keys in a dictionary</fsummary>
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<v>Key = Value = term()</v>
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<v>Orddict1 = Orddict2 = ordered_dictionary()</v>
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<p>This function appends a new <c>Value</c> to the current list
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of values associated with <c>Key</c>. An exception is
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generated if the initial value associated with <c>Key</c> is
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not a list of values.</p>
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<name>append_list(Key, ValList, Orddict1) -> Orddict2</name>
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<fsummary>Append new values to keys in a dictionary</fsummary>
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<v>ValList = [Value]</v>
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<v>Key = Value = term()</v>
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<v>Orddict1 = Orddict2 = ordered_dictionary()</v>
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<p>This function appends a list of values <c>ValList</c> to
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the current list of values associated with <c>Key</c>. An
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exception is generated if the initial value associated with
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<c>Key</c> is not a list of values.</p>
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<name>erase(Key, Orddict1) -> Orddict2</name>
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<fsummary>Erase a key from a dictionary</fsummary>
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<v>Orddict1 = Orddict2 = ordered_dictionary()</v>
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<p>This function erases all items with a given key from a
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<name>fetch(Key, Orddict) -> Value</name>
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<fsummary>Look-up values in a dictionary</fsummary>
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<v>Key = Value = term()</v>
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<v>Orddict = ordered_dictionary()</v>
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<p>This function returns the value associated with <c>Key</c>
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in the dictionary <c>Orddict</c>. <c>fetch</c> assumes that
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the <c>Key</c> is present in the dictionary and an exception
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is generated if <c>Key</c> is not in the dictionary.</p>
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<name>fetch_keys(Orddict) -> Keys</name>
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<fsummary>Return all keys in a dictionary</fsummary>
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<v>Orddict = ordered_dictionary()</v>
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<v>Keys = [term()]</v>
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<p>This function returns a list of all keys in the dictionary.</p>
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<name>filter(Pred, Orddict1) -> Orddict2</name>
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<fsummary>Choose elements which satisfy a predicate</fsummary>
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<v>Pred = fun(Key, Value) -> bool()</v>
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<v> Key = Value = term()</v>
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<v>Orddict1 = Orddict2 = ordered_dictionary()</v>
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<p><c>Orddict2</c> is a dictionary of all keys and values in
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<c>Orddict1</c> for which <c>Pred(Key, Value)</c> is <c>true</c>.</p>
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<name>find(Key, Orddict) -> {ok, Value} | error</name>
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<fsummary>Search for a key in a dictionary</fsummary>
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<v>Key = Value = term()</v>
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<v>Orddict = ordered_dictionary()</v>
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<p>This function searches for a key in a dictionary. Returns
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<c>{ok, Value}</c> where <c>Value</c> is the value associated
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with <c>Key</c>, or <c>error</c> if the key is not present in
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<name>fold(Fun, Acc0, Orddict) -> Acc1</name>
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<fsummary>Fold a function over a dictionary</fsummary>
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<v>Fun = fun(Key, Value, AccIn) -> AccOut</v>
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<v>Key = Value = term()</v>
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<v>Acc0 = Acc1 = AccIn = AccOut = term()</v>
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<v>Orddict = ordered_dictionary()</v>
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<p>Calls <c>Fun</c> on successive keys and values of
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<c>Orddict</c> together with an extra argument <c>Acc</c>
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(short for accumulator). <c>Fun</c> must return a new
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accumulator which is passed to the next call. <c>Acc0</c> is
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returned if the list is empty. The evaluation order is
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<name>from_list(List) -> Orddict</name>
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<fsummary>Convert a list of pairs to a dictionary</fsummary>
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<v>List = [{Key, Value}]</v>
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<v>Orddict = ordered_dictionary()</v>
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<p>This function converts the key/value list <c>List</c> to a
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<name>is_key(Key, Orddict) -> bool()</name>
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<fsummary>Test if a key is in a dictionary</fsummary>
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<v>Orddict = ordered_dictionary()</v>
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<p>This function tests if <c>Key</c> is contained in
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the dictionary <c>Orddict</c>.</p>
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<name>map(Fun, Orddict1) -> Orddict2</name>
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<fsummary>Map a function over a dictionary</fsummary>
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<v>Fun = fun(Key, Value1) -> Value2</v>
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<v> Key = Value1 = Value2 = term()</v>
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<v>Orddict1 = Orddict2 = ordered_dictionary()</v>
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<p><c>map</c> calls <c>Func</c> on successive keys and values
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of <c>Orddict</c> to return a new value for each key.
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The evaluation order is undefined.</p>
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<name>merge(Fun, Orddict1, Orddict2) -> Orddict3</name>
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<fsummary>Merge two dictionaries</fsummary>
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<v>Fun = fun(Key, Value1, Value2) -> Value</v>
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<v> Key = Value1 = Value2 = Value3 = term()</v>
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<v>Orddict1 = Orddict2 = Orddict3 = ordered_dictionary()</v>
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<p><c>merge</c> merges two dictionaries, <c>Orddict1</c> and
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<c>Orddict2</c>, to create a new dictionary. All the <c>Key</c>
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- <c>Value</c> pairs from both dictionaries are included in
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the new dictionary. If a key occurs in both dictionaries then
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<c>Fun</c> is called with the key and both values to return a
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new value. <c>merge</c> could be defined as:</p>
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merge(Fun, D1, D2) ->
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fold(fun (K, V1, D) ->
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update(K, fun (V2) -> Fun(K, V1, V2) end, V1, D)
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<p>but is faster.</p>
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<name>new() -> ordered_dictionary()</name>
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<fsummary>Create a dictionary</fsummary>
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<p>This function creates a new dictionary.</p>
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<name>size(Orddict) -> int()</name>
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<fsummary>Return the number of elements in an ordered dictionary</fsummary>
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<v>Orddict = ordered_dictionary()</v>
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<p>Returns the number of elements in an <c>Orddict</c>.</p>
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<name>store(Key, Value, Orddict1) -> Orddict2</name>
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<fsummary>Store a value in a dictionary</fsummary>
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<v>Key = Value = term()</v>
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<v>Orddict1 = Orddict2 = ordered_dictionary()</v>
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<p>This function stores a <c>Key</c> - <c>Value</c> pair in a
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dictionary. If the <c>Key</c> already exists in <c>Orddict1</c>,
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the associated value is replaced by <c>Value</c>.</p>
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<name>to_list(Orddict) -> List</name>
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<fsummary>Convert a dictionary to a list of pairs</fsummary>
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<v>Orddict = ordered_dictionary()</v>
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<v>List = [{Key, Value}]</v>
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<p>This function converts the dictionary to a list
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<name>update(Key, Fun, Orddict1) -> Orddict2</name>
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<fsummary>Update a value in a dictionary</fsummary>
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<v>Fun = fun(Value1) -> Value2</v>
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<v> Value1 = Value2 = term()</v>
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<v>Orddict1 = Orddict2 = ordered_dictionary()</v>
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<p>Update the a value in a dictionary by calling <c>Fun</c> on
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the value to get a new value. An exception is generated if
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<c>Key</c> is not present in the dictionary.</p>
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<name>update(Key, Fun, Initial, Orddict1) -> Orddict2</name>
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<fsummary>Update a value in a dictionary</fsummary>
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<v>Key = Initial = term()</v>
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<v>Fun = fun(Value1) -> Value2</v>
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<v> Value1 = Value2 = term()</v>
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<v>Orddict1 = Orddict2 = ordered_dictionary()</v>
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<p>Update the a value in a dictionary by calling <c>Fun</c> on
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the value to get a new value. If <c>Key</c> is not present
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in the dictionary then <c>Initial</c> will be stored as
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the first value. For example <c>append/3</c> could be defined
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append(Key, Val, D) ->
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update(Key, fun (Old) -> Old ++ [Val] end, [Val], D).</code>
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<name>update_counter(Key, Increment, Orddict1) -> Orddict2</name>
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<fsummary>Increment a value in a dictionary</fsummary>
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<v>Increment = number()</v>
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<v>Orddict1 = Orddict2 = ordered_dictionary()</v>
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<p>Add <c>Increment</c> to the value associated with <c>Key</c>
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and store this value. If <c>Key</c> is not present in
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the dictionary then <c>Increment</c> will be stored as
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<p>This could be defined as:</p>
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update_counter(Key, Incr, D) ->
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update(Key, fun (Old) -> Old + Incr end, Incr, D).</code>
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<p>but is faster.</p>
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<p>The functions <c>append</c> and <c>append_list</c> are included
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so we can store keyed values in a list <em>accumulator</em>. For
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> D0 = orddict:new(),
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D1 = orddict:store(files, [], D0),
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D2 = orddict:append(files, f1, D1),
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D3 = orddict:append(files, f2, D2),
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D4 = orddict:append(files, f3, D3),
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orddict:fetch(files, D4).
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<p>This saves the trouble of first fetching a keyed value,
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appending a new value to the list of stored values, and storing
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<p>The function <c>fetch</c> should be used if the key is known to
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be in the dictionary, otherwise <c>find</c>.</p>
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<title>See Also</title>
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<p><seealso marker="dict">dict(3)</seealso>,
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<seealso marker="gb_trees">gb_trees(3)</seealso></p>
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lib/stdlib/doc/src/orddict.xml
