
gb_sets(3erl) Erlang Module Definition gb_sets(3erl)
NAME
gb_sets  General Balanced Trees
DESCRIPTION
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.
This module considers two elements as different if and only if they do not compare equal (
== ).
COMPLEXITY NOTE
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 orderedlist 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 100200 elements), and repeatedly testing for
membership in the current set.
As with normal tree structures, lookup (membership testing), insertion and deletion have
logarithmic complexity.
COMPATIBILITY
All of the following functions in this module also exist and do the same thing in the sets
and ordsets modules. That is, by only changing the module name for each call, you can try
out different set representations.
* add_element/2
* del_element/2
* filter/2
* fold/3
* from_list/1
* intersection/1
* intersection/2
* is_element/2
* is_set/1
* is_subset/2
* new/0
* size/1
* subtract/2
* to_list/1
* union/1
* union/2
DATA TYPES
gb_set() = a GB set
EXPORTS
add(Element, Set1) > Set2
add_element(Element, Set1) > Set2
Types Element = term()
Set1 = Set2 = gb_set()
Returns a new gb_set formed from Set1 with Element inserted. If Element is already
an element in Set1 , nothing is changed.
balance(Set1) > Set2
Types Set1 = Set2 = gb_set()
Rebalances the tree representation of Set1 . 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 min
imise lookup times, since deletion only does not rebalance the tree.
delete(Element, Set1) > Set2
Types Element = term()
Set1 = Set2 = gb_set()
Returns a new gb_set formed from Set1 with Element removed. Assumes that Element is
present in Set1 .
delete_any(Element, Set1) > Set2
del_element(Element, Set1) > Set2
Types Element = term()
Set1 = Set2 = gb_set()
Returns a new gb_set formed from Set1 with Element removed. If Element is not an
element in Set1 , nothing is changed.
difference(Set1, Set2) > Set3
subtract(Set1, Set2) > Set3
Types Set1 = Set2 = Set3 = gb_set()
Returns only the elements of Set1 which are not also elements of Set2 .
empty() > Set
new() > Set
Types Set = gb_set()
Returns a new empty gb_set.
filter(Pred, Set1) > Set2
Types Pred = fun (E) > bool()
E = term()
Set1 = Set2 = gb_set()
Filters elements in Set1 using predicate function Pred .
fold(Function, Acc0, Set) > Acc1
Types Function = fun (E, AccIn) > AccOut
Acc0 = Acc1 = AccIn = AccOut = term()
E = term()
Set = gb_set()
Folds Function over every element in Set returning the final value of the accumula
tor.
from_list(List) > Set
Types List = [term()]
Set = gb_set()
Returns a gb_set of the elements in List , where List may be unordered and contain
duplicates.
from_ordset(List) > Set
Types List = [term()]
Set = gb_set()
Turns an orderedset list List into a gb_set. The list must not contain duplicates.
insert(Element, Set1) > Set2
Types Element = term()
Set1 = Set2 = gb_set()
Returns a new gb_set formed from Set1 with Element inserted. Assumes that Element
is not present in Set1 .
intersection(Set1, Set2) > Set3
Types Set1 = Set2 = Set3 = gb_set()
Returns the intersection of Set1 and Set2 .
intersection(SetList) > Set
Types SetList = [gb_set()]
Set = gb_set()
Returns the intersection of the nonempty list of gb_sets.
is_disjoint(Set1, Set2) > bool()
Types Set1 = Set2 = gb_set()
Returns true if Set1 and Set2 are disjoint (have no elements in common), and false
otherwise.
is_empty(Set) > bool()
Types Set = gb_set()
Returns true if Set is an empty set, and false otherwise.
is_member(Element, Set) > bool()
is_element(Element, Set) > bool()
Types Element = term()
Set = gb_set()
Returns true if Element is an element of Set , otherwise false .
is_set(Term) > bool()
Types Term = term()
Returns true if Set appears to be a gb_set, otherwise false .
is_subset(Set1, Set2) > bool()
Types Set1 = Set2 = gb_set()
Returns true when every element of Set1 is also a member of Set2 , otherwise false
.
iterator(Set) > Iter
Types Set = gb_set()
Iter = term()
Returns an iterator that can be used for traversing the entries of Set ; see next/1
. The implementation of this is very efficient; traversing the whole set using
next/1 is only slightly slower than getting the list of all elements using
to_list/1 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.
largest(Set) > term()
Types Set = gb_set()
Returns the largest element in Set . Assumes that Set is nonempty.
next(Iter1) > {Element, Iter2}  none
Types Iter1 = Iter2 = Element = term()
Returns {Element, Iter2} where Element is the smallest element referred to by the
iterator Iter1 , and Iter2 is the new iterator to be used for traversing the
remaining elements, or the atom none if no elements remain.
singleton(Element) > gb_set()
Types Element = term()
Returns a gb_set containing only the element Element .
size(Set) > int()
Types Set = gb_set()
Returns the number of elements in Set .
smallest(Set) > term()
Types Set = gb_set()
Returns the smallest element in Set . Assumes that Set is nonempty.
take_largest(Set1) > {Element, Set2}
Types Set1 = Set2 = gb_set()
Element = term()
Returns {Element, Set2} , where Element is the largest element in Set1 , and Set2
is this set with Element deleted. Assumes that Set1 is nonempty.
take_smallest(Set1) > {Element, Set2}
Types Set1 = Set2 = gb_set()
Element = term()
Returns {Element, Set2} , where Element is the smallest element in Set1 , and Set2
is this set with Element deleted. Assumes that Set1 is nonempty.
to_list(Set) > List
Types Set = gb_set()
List = [term()]
Returns the elements of Set as a list.
union(Set1, Set2) > Set3
Types Set1 = Set2 = Set3 = gb_set()
Returns the merged (union) gb_set of Set1 and Set2 .
union(SetList) > Set
Types SetList = [gb_set()]
Set = gb_set()
Returns the merged (union) gb_set of the list of gb_sets.
SEE ALSO
gb_trees(3erl) , ordsets(3erl) , sets(3erl)
Ericsson AB stdlib 1.17.3 gb_sets(3erl) 
