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+<?xml version="1.0" encoding="latin1" ?>
+<!DOCTYPE erlref SYSTEM "erlref.dtd">
+
+<erlref>
+ <header>
+ <copyright>
+ <year>1996</year><year>2009</year>
+ <holder>Ericsson AB. All Rights Reserved.</holder>
+ </copyright>
+ <legalnotice>
+ 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.
+
+ </legalnotice>
+
+ <title>dict</title>
+ <prepared>Robert Virding</prepared>
+ <docno></docno>
+ <date>1997-01-15</date>
+ <rev>B</rev>
+ </header>
+ <module>dict</module>
+ <modulesummary>Key-Value Dictionary</modulesummary>
+ <description>
+ <p><c>Dict</c> implements a <c>Key</c> - <c>Value</c> dictionary.
+ The representation of a dictionary is not defined.</p>
+ <p>This module provides exactly the same interface as the module
+ <c>orddict</c>. One difference is that while this module
+ considers two keys as different if they do not match (<c>=:=</c>),
+ <c>orddict</c> considers two keys as different if and only if
+ they do not compare equal (<c>==</c>).</p>
+ </description>
+
+ <section>
+ <title>DATA TYPES</title>
+ <code type="none">
+dictionary()
+ as returned by new/0</code>
+ </section>
+ <funcs>
+ <func>
+ <name>append(Key, Value, Dict1) -> Dict2</name>
+ <fsummary>Append a value to keys in a dictionary</fsummary>
+ <type>
+ <v>Key = Value = term()</v>
+ <v>Dict1 = Dict2 = dictionary()</v>
+ </type>
+ <desc>
+ <p>This function appends a new <c>Value</c> to the current list
+ of values associated with <c>Key</c>. An exception is
+ generated if the initial value associated with <c>Key</c> is
+ not a list of values.</p>
+ </desc>
+ </func>
+ <func>
+ <name>append_list(Key, ValList, Dict1) -> Dict2</name>
+ <fsummary>Append new values to keys in a dictionary</fsummary>
+ <type>
+ <v>ValList = [Value]</v>
+ <v>Key = Value = term()</v>
+ <v>Dict1 = Dict2 = dictionary()</v>
+ </type>
+ <desc>
+ <p>This function appends a list of values <c>ValList</c> to
+ the current list of values associated with <c>Key</c>. An
+ exception is generated if the initial value associated with
+ <c>Key</c> is not a list of values.</p>
+ </desc>
+ </func>
+ <func>
+ <name>erase(Key, Dict1) -> Dict2</name>
+ <fsummary>Erase a key from a dictionary</fsummary>
+ <type>
+ <v>Key = term()</v>
+ <v>Dict1 = Dict2 = dictionary()</v>
+ </type>
+ <desc>
+ <p>This function erases all items with a given key from a
+ dictionary.</p>
+ </desc>
+ </func>
+ <func>
+ <name>fetch(Key, Dict) -> Value</name>
+ <fsummary>Look-up values in a dictionary</fsummary>
+ <type>
+ <v>Key = Value = term()</v>
+ <v>Dict = dictionary()</v>
+ </type>
+ <desc>
+ <p>This function returns the value associated with <c>Key</c>
+ in the dictionary <c>Dict</c>. <c>fetch</c> assumes that
+ the <c>Key</c> is present in the dictionary and an exception
+ is generated if <c>Key</c> is not in the dictionary.</p>
+ </desc>
+ </func>
+ <func>
+ <name>fetch_keys(Dict) -> Keys</name>
+ <fsummary>Return all keys in a dictionary</fsummary>
+ <type>
+ <v>Dict = dictionary()</v>
+ <v>Keys = [term()]</v>
+ </type>
+ <desc>
+ <p>This function returns a list of all keys in the dictionary.</p>
+ </desc>
+ </func>
+ <func>
+ <name>filter(Pred, Dict1) -> Dict2</name>
+ <fsummary>Choose elements which satisfy a predicate</fsummary>
+ <type>
+ <v>Pred = fun(Key, Value) -> bool()</v>
+ <v>&nbsp;Key = Value = term()</v>
+ <v>Dict1 = Dict2 = dictionary()</v>
+ </type>
+ <desc>
+ <p><c>Dict2</c> is a dictionary of all keys and values in
+ <c>Dict1</c> for which <c>Pred(Key, Value)</c> is <c>true</c>.</p>
+ </desc>
+ </func>
+ <func>
+ <name>find(Key, Dict) -> {ok, Value} | error</name>
+ <fsummary>Search for a key in a dictionary</fsummary>
+ <type>
+ <v>Key = Value = term()</v>
+ <v>Dict = dictionary()</v>
+ </type>
+ <desc>
+ <p>This function searches for a key in a dictionary. Returns
+ <c>{ok, Value}</c> where <c>Value</c> is the value associated
+ with <c>Key</c>, or <c>error</c> if the key is not present in
+ the dictionary.</p>
+ </desc>
+ </func>
+ <func>
+ <name>fold(Fun, Acc0, Dict) -> Acc1</name>
+ <fsummary>Fold a function over a dictionary</fsummary>
+ <type>
+ <v>Fun = fun(Key, Value, AccIn) -> AccOut</v>
+ <v>Key = Value = term()</v>
+ <v>Acc0 = Acc1 = AccIn = AccOut = term()</v>
+ <v>Dict = dictionary()</v>
+ </type>
+ <desc>
+ <p>Calls <c>Fun</c> on successive keys and values of
+ <c>Dict</c> together with an extra argument <c>Acc</c>
+ (short for accumulator). <c>Fun</c> must return a new
+ accumulator which is passed to the next call. <c>Acc0</c> is
+ returned if the list is empty. The evaluation order is
+ undefined.</p>
+ </desc>
+ </func>
+ <func>
+ <name>from_list(List) -> Dict</name>
+ <fsummary>Convert a list of pairs to a dictionary</fsummary>
+ <type>
+ <v>List = [{Key, Value}]</v>
+ <v>Dict = dictionary()</v>
+ </type>
+ <desc>
+ <p>This function converts the key/value list <c>List</c> to a
+ dictionary.</p>
+ </desc>
+ </func>
+ <func>
+ <name>is_key(Key, Dict) -> bool()</name>
+ <fsummary>Test if a key is in a dictionary</fsummary>
+ <type>
+ <v>Key = term()</v>
+ <v>Dict = dictionary()</v>
+ </type>
+ <desc>
+ <p>This function tests if <c>Key</c> is contained in
+ the dictionary <c>Dict</c>.</p>
+ </desc>
+ </func>
+ <func>
+ <name>map(Fun, Dict1) -> Dict2</name>
+ <fsummary>Map a function over a dictionary</fsummary>
+ <type>
+ <v>Fun = fun(Key, Value1) -> Value2</v>
+ <v>&nbsp;Key = Value1 = Value2 = term()</v>
+ <v>Dict1 = Dict2 = dictionary()</v>
+ </type>
+ <desc>
+ <p><c>map</c> calls <c>Func</c> on successive keys and values
+ of <c>Dict</c> to return a new value for each key.
+ The evaluation order is undefined.</p>
+ </desc>
+ </func>
+ <func>
+ <name>merge(Fun, Dict1, Dict2) -> Dict3</name>
+ <fsummary>Merge two dictionaries</fsummary>
+ <type>
+ <v>Fun = fun(Key, Value1, Value2) -> Value</v>
+ <v>&nbsp;Key = Value1 = Value2 = Value3 = term()</v>
+ <v>Dict1 = Dict2 = Dict3 = dictionary()</v>
+ </type>
+ <desc>
+ <p><c>merge</c> merges two dictionaries, <c>Dict1</c> and
+ <c>Dict2</c>, to create a new dictionary. All the <c>Key</c>
+ - <c>Value</c> pairs from both dictionaries are included in
+ the new dictionary. If a key occurs in both dictionaries then
+ <c>Fun</c> is called with the key and both values to return a
+ new value. <c>merge</c> could be defined as:</p>
+ <code type="none">
+merge(Fun, D1, D2) ->
+ fold(fun (K, V1, D) ->
+ update(K, fun (V2) -> Fun(K, V1, V2) end, V1, D)
+ end, D2, D1).</code>
+ <p>but is faster.</p>
+ </desc>
+ </func>
+ <func>
+ <name>new() -> dictionary()</name>
+ <fsummary>Create a dictionary</fsummary>
+ <desc>
+ <p>This function creates a new dictionary.</p>
+ </desc>
+ </func>
+ <func>
+ <name>size(Dict) -> int()</name>
+ <fsummary>Return the number of elements in a dictionary</fsummary>
+ <type>
+ <v>Dict = dictionary()</v>
+ </type>
+ <desc>
+ <p>Returns the number of elements in a <c>Dict</c>.</p>
+ </desc>
+ </func>
+ <func>
+ <name>store(Key, Value, Dict1) -> Dict2</name>
+ <fsummary>Store a value in a dictionary</fsummary>
+ <type>
+ <v>Key = Value = term()</v>
+ <v>Dict1 = Dict2 = dictionary()</v>
+ </type>
+ <desc>
+ <p>This function stores a <c>Key</c> - <c>Value</c> pair in a
+ dictionary. If the <c>Key</c> already exists in <c>Dict1</c>,
+ the associated value is replaced by <c>Value</c>.</p>
+ </desc>
+ </func>
+ <func>
+ <name>to_list(Dict) -> List</name>
+ <fsummary>Convert a dictionary to a list of pairs</fsummary>
+ <type>
+ <v>Dict = dictionary()</v>
+ <v>List = [{Key, Value}]</v>
+ </type>
+ <desc>
+ <p>This function converts the dictionary to a list
+ representation.</p>
+ </desc>
+ </func>
+ <func>
+ <name>update(Key, Fun, Dict1) -> Dict2</name>
+ <fsummary>Update a value in a dictionary</fsummary>
+ <type>
+ <v>Key = term()</v>
+ <v>Fun = fun(Value1) -> Value2</v>
+ <v>&nbsp;Value1 = Value2 = term()</v>
+ <v>Dict1 = Dict2 = dictionary()</v>
+ </type>
+ <desc>
+ <p>Update the a value in a dictionary by calling <c>Fun</c> on
+ the value to get a new value. An exception is generated if
+ <c>Key</c> is not present in the dictionary.</p>
+ </desc>
+ </func>
+ <func>
+ <name>update(Key, Fun, Initial, Dict1) -> Dict2</name>
+ <fsummary>Update a value in a dictionary</fsummary>
+ <type>
+ <v>Key = Initial = term()</v>
+ <v>Fun = fun(Value1) -> Value2</v>
+ <v>&nbsp;Value1 = Value2 = term()</v>
+ <v>Dict1 = Dict2 = dictionary()</v>
+ </type>
+ <desc>
+ <p>Update the a value in a dictionary by calling <c>Fun</c> on
+ the value to get a new value. If <c>Key</c> is not present
+ in the dictionary then <c>Initial</c> will be stored as
+ the first value. For example <c>append/3</c> could be defined
+ as:</p>
+ <code type="none">
+append(Key, Val, D) ->
+ update(Key, fun (Old) -> Old ++ [Val] end, [Val], D).</code>
+ </desc>
+ </func>
+ <func>
+ <name>update_counter(Key, Increment, Dict1) -> Dict2</name>
+ <fsummary>Increment a value in a dictionary</fsummary>
+ <type>
+ <v>Key = term()</v>
+ <v>Increment = number()</v>
+ <v>Dict1 = Dict2 = dictionary()</v>
+ </type>
+ <desc>
+ <p>Add <c>Increment</c> to the value associated with <c>Key</c>
+ and store this value. If <c>Key</c> is not present in
+ the dictionary then <c>Increment</c> will be stored as
+ the first value.</p>
+ <p>This could be defined as:</p>
+ <code type="none">
+update_counter(Key, Incr, D) ->
+ update(Key, fun (Old) -> Old + Incr end, Incr, D).</code>
+ <p>but is faster.</p>
+ </desc>
+ </func>
+ </funcs>
+
+ <section>
+ <title>Notes</title>
+ <p>The functions <c>append</c> and <c>append_list</c> are included
+ so we can store keyed values in a list <em>accumulator</em>. For
+ example:</p>
+ <pre>
+> 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] </pre>
+ <p>This saves the trouble of first fetching a keyed value,
+ appending a new value to the list of stored values, and storing
+ the result.
+ </p>
+ <p>The function <c>fetch</c> should be used if the key is known to
+ be in the dictionary, otherwise <c>find</c>.</p>
+ </section>
+
+ <section>
+ <title>See Also</title>
+ <p><seealso marker="gb_trees">gb_trees(3)</seealso>,
+ <seealso marker="orddict">orddict(3)</seealso></p>
+ </section>
+</erlref>
+