<?xml version="1.0" encoding="latin1" ?> <!DOCTYPE erlref SYSTEM "erlref.dtd"> <erlref> <header> <copyright> <year>2001</year><year>2011</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>gb_sets</title> <prepared></prepared> <docno></docno> <date></date> <rev></rev> </header> <module>gb_sets</module> <modulesummary>General Balanced Trees</modulesummary> <description> <p>An implementation of ordered sets using Prof. Arne Andersson's General Balanced Trees. This can be much more efficient than using ordered lists, for larger sets, but depends on the application.</p> <p>This module considers two elements as different if and only if they do not compare equal (<c>==</c>).</p> </description> <section> <title>Complexity note</title> <p>The complexity on set operations is bounded by either O(|S|) or O(|T| * log(|S|)), where S is the largest given set, depending on which is fastest for any particular function call. For operating on sets of almost equal size, this implementation is about 3 times slower than using ordered-list sets directly. For sets of very different sizes, however, this solution can be arbitrarily much faster; in practical cases, often between 10 and 100 times. This implementation is particularly suited for accumulating elements a few at a time, building up a large set (more than 100-200 elements), and repeatedly testing for membership in the current set.</p> <p>As with normal tree structures, lookup (membership testing), insertion and deletion have logarithmic complexity.</p> </section> <section> <title>Compatibility</title> <p>All of the following functions in this module also exist and do the same thing in the <c>sets</c> and <c>ordsets</c> modules. That is, by only changing the module name for each call, you can try out different set representations.</p> <list type="bulleted"> <item> <p><c>add_element/2</c></p> </item> <item> <p><c>del_element/2</c></p> </item> <item> <p><c>filter/2</c></p> </item> <item> <p><c>fold/3</c></p> </item> <item> <p><c>from_list/1</c></p> </item> <item> <p><c>intersection/1</c></p> </item> <item> <p><c>intersection/2</c></p> </item> <item> <p><c>is_element/2</c></p> </item> <item> <p><c>is_set/1</c></p> </item> <item> <p><c>is_subset/2</c></p> </item> <item> <p><c>new/0</c></p> </item> <item> <p><c>size/1</c></p> </item> <item> <p><c>subtract/2</c></p> </item> <item> <p><c>to_list/1</c></p> </item> <item> <p><c>union/1</c></p> </item> <item> <p><c>union/2</c></p> </item> </list> </section> <datatypes> <datatype> <name><marker id="type-gb_set">gb_set()</marker></name> <desc><p>A GB set.</p></desc> </datatype> <datatype> <name name="iter"/> <desc><p>A GB set iterator.</p></desc> </datatype> </datatypes> <funcs> <func> <name name="add" arity="2"/> <name name="add_element" arity="2"/> <fsummary>Add a (possibly existing) element to a gb_set</fsummary> <desc> <p>Returns a new gb_set formed from <c><anno>Set1</anno></c> with <c><anno>Element</anno></c> inserted. If <c><anno>Element</anno></c> is already an element in <c><anno>Set1</anno></c>, nothing is changed.</p> </desc> </func> <func> <name name="balance" arity="1"/> <fsummary>Rebalance tree representation of a gb_set</fsummary> <desc> <p>Rebalances the tree representation of <c><anno>Set1</anno></c>. Note that this is rarely necessary, but may be motivated when a large number of elements have been deleted from the tree without further insertions. Rebalancing could then be forced in order to minimise lookup times, since deletion only does not rebalance the tree.</p> </desc> </func> <func> <name name="delete" arity="2"/> <fsummary>Remove an element from a gb_set</fsummary> <desc> <p>Returns a new gb_set formed from <c><anno>Set1</anno></c> with <c><anno>Element</anno></c> removed. Assumes that <c><anno>Element</anno></c> is present in <c><anno>Set1</anno></c>.</p> </desc> </func> <func> <name name="delete_any" arity="2"/> <name name="del_element" arity="2"/> <fsummary>Remove a (possibly non-existing) element from a gb_set</fsummary> <desc> <p>Returns a new gb_set formed from <c><anno>Set1</anno></c> with <c><anno>Element</anno></c> removed. If <c><anno>Element</anno></c> is not an element in <c><anno>Set1</anno></c>, nothing is changed.</p> </desc> </func> <func> <name name="difference" arity="2"/> <name name="subtract" arity="2"/> <fsummary>Return the difference of two gb_sets</fsummary> <desc> <p>Returns only the elements of <c><anno>Set1</anno></c> which are not also elements of <c><anno>Set2</anno></c>.</p> </desc> </func> <func> <name name="empty" arity="0"/> <name name="new" arity="0"/> <fsummary>Return an empty gb_set</fsummary> <desc> <p>Returns a new empty gb_set.</p> </desc> </func> <func> <name name="filter" arity="2"/> <fsummary>Filter gb_set elements</fsummary> <desc> <p>Filters elements in <c><anno>Set1</anno></c> using predicate function <c><anno>Pred</anno></c>.</p> </desc> </func> <func> <name name="fold" arity="3"/> <fsummary>Fold over gb_set elements</fsummary> <desc> <p>Folds <c><anno>Function</anno></c> over every element in <c><anno>Set</anno></c> returning the final value of the accumulator.</p> </desc> </func> <func> <name name="from_list" arity="1"/> <fsummary>Convert a list into a gb_set</fsummary> <desc> <p>Returns a gb_set of the elements in <c><anno>List</anno></c>, where <c><anno>List</anno></c> may be unordered and contain duplicates.</p> </desc> </func> <func> <name name="from_ordset" arity="1"/> <fsummary>Make a gb_set from an ordset list</fsummary> <desc> <p>Turns an ordered-set list <c><anno>List</anno></c> into a gb_set. The list must not contain duplicates.</p> </desc> </func> <func> <name name="insert" arity="2"/> <fsummary>Add a new element to a gb_set</fsummary> <desc> <p>Returns a new gb_set formed from <c><anno>Set1</anno></c> with <c><anno>Element</anno></c> inserted. Assumes that <c><anno>Element</anno></c> is not present in <c><anno>Set1</anno></c>.</p> </desc> </func> <func> <name name="intersection" arity="2"/> <fsummary>Return the intersection of two gb_sets</fsummary> <desc> <p>Returns the intersection of <c><anno>Set1</anno></c> and <c><anno>Set2</anno></c>.</p> </desc> </func> <func> <name name="intersection" arity="1"/> <fsummary>Return the intersection of a list of gb_sets</fsummary> <desc> <p>Returns the intersection of the non-empty list of gb_sets.</p> </desc> </func> <func> <name name="is_disjoint" arity="2"/> <fsummary>Check whether two gb_sets are disjoint</fsummary> <desc> <p>Returns <c>true</c> if <c><anno>Set1</anno></c> and <c><anno>Set2</anno></c> are disjoint (have no elements in common), and <c>false</c> otherwise.</p> </desc> </func> <func> <name name="is_empty" arity="1"/> <fsummary>Test for empty gb_set</fsummary> <desc> <p>Returns <c>true</c> if <c><anno>Set</anno></c> is an empty set, and <c>false</c> otherwise.</p> </desc> </func> <func> <name name="is_member" arity="2"/> <name name="is_element" arity="2"/> <fsummary>Test for membership of a gb_set</fsummary> <desc> <p>Returns <c>true</c> if <c><anno>Element</anno></c> is an element of <c><anno>Set</anno></c>, otherwise <c>false</c>.</p> </desc> </func> <func> <name name="is_set" arity="1"/> <fsummary>Test for a gb_set</fsummary> <desc> <p>Returns <c>true</c> if <c><anno>Term</anno></c> appears to be a gb_set, otherwise <c>false</c>.</p> </desc> </func> <func> <name name="is_subset" arity="2"/> <fsummary>Test for subset</fsummary> <desc> <p>Returns <c>true</c> when every element of <c><anno>Set1</anno></c> is also a member of <c><anno>Set2</anno></c>, otherwise <c>false</c>.</p> </desc> </func> <func> <name name="iterator" arity="1"/> <fsummary>Return an iterator for a gb_set</fsummary> <desc> <p>Returns an iterator that can be used for traversing the entries of <c><anno>Set</anno></c>; see <c>next/1</c>. The implementation of this is very efficient; traversing the whole set using <c>next/1</c> is only slightly slower than getting the list of all elements using <c>to_list/1</c> and traversing that. The main advantage of the iterator approach is that it does not require the complete list of all elements to be built in memory at one time.</p> </desc> </func> <func> <name name="largest" arity="1"/> <fsummary>Return largest element</fsummary> <desc> <p>Returns the largest element in <c><anno>Set</anno></c>. Assumes that <c><anno>Set</anno></c> is nonempty.</p> </desc> </func> <func> <name name="next" arity="1"/> <fsummary>Traverse a gb_set with an iterator</fsummary> <desc> <p>Returns <c>{<anno>Element</anno>, <anno>Iter2</anno>}</c> where <c><anno>Element</anno></c> is the smallest element referred to by the iterator <c><anno>Iter1</anno></c>, and <c><anno>Iter2</anno></c> is the new iterator to be used for traversing the remaining elements, or the atom <c>none</c> if no elements remain.</p> </desc> </func> <func> <name name="singleton" arity="1"/> <fsummary>Return a gb_set with one element</fsummary> <desc> <p>Returns a gb_set containing only the element <c><anno>Element</anno></c>.</p> </desc> </func> <func> <name name="size" arity="1"/> <fsummary>Return the number of elements in a gb_set</fsummary> <desc> <p>Returns the number of elements in <c><anno>Set</anno></c>.</p> </desc> </func> <func> <name name="smallest" arity="1"/> <fsummary>Return smallest element</fsummary> <desc> <p>Returns the smallest element in <c><anno>Set</anno></c>. Assumes that <c><anno>Set</anno></c> is nonempty.</p> </desc> </func> <func> <name name="take_largest" arity="1"/> <fsummary>Extract largest element</fsummary> <desc> <p>Returns <c>{<anno>Element</anno>, <anno>Set2</anno>}</c>, where <c><anno>Element</anno></c> is the largest element in <c><anno>Set1</anno></c>, and <c><anno>Set2</anno></c> is this set with <c><anno>Element</anno></c> deleted. Assumes that <c><anno>Set1</anno></c> is nonempty.</p> </desc> </func> <func> <name name="take_smallest" arity="1"/> <fsummary>Extract smallest element</fsummary> <desc> <p>Returns <c>{<anno>Element</anno>, <anno>Set2</anno>}</c>, where <c><anno>Element</anno></c> is the smallest element in <c><anno>Set1</anno></c>, and <c><anno>Set2</anno></c> is this set with <c><anno>Element</anno></c> deleted. Assumes that <c><anno>Set1</anno></c> is nonempty.</p> </desc> </func> <func> <name name="to_list" arity="1"/> <fsummary>Convert a gb_set into a list</fsummary> <desc> <p>Returns the elements of <c><anno>Set</anno></c> as a list.</p> </desc> </func> <func> <name name="union" arity="2"/> <fsummary>Return the union of two gb_sets</fsummary> <desc> <p>Returns the merged (union) gb_set of <c><anno>Set1</anno></c> and <c><anno>Set2</anno></c>.</p> </desc> </func> <func> <name name="union" arity="1"/> <fsummary>Return the union of a list of gb_sets</fsummary> <desc> <p>Returns the merged (union) gb_set of the list of gb_sets.</p> </desc> </func> </funcs> <section> <title>SEE ALSO</title> <p><seealso marker="gb_trees">gb_trees(3)</seealso>, <seealso marker="ordsets">ordsets(3)</seealso>, <seealso marker="sets">sets(3)</seealso></p> </section> </erlref>