Set::Scalar - basic set operations |
Set::Scalar - basic set operations
use Set::Scalar; $s = Set::Scalar->new; $s->insert('a', 'b'); $s->delete('b'); $t = Set::Scalar->new('x', 'y', $z);
$s = Set::Scalar->new; $s = Set::Scalar->new(@members);
$t = $s->clone; $t = $s->copy; # clone of clone
$s->insert(@members); $s->delete(@members); $s->invert(@members); # insert if hasn't, delete if has
$s->clear; # removes all the elements
Note that clear()
only releases the memory used by the set to
be reused by Perl; it will not reduce the overall memory use.
print $s, "\n";
The display format of a set is the members of the set separated by spaces and enclosed in parentheses ().
You can even display recursive sets.
See Customising Display for customising the set display.
@members = $s->members; @elements = $s->elements; # alias for members
$size = $s->size; # the number of members
$s->has($m) # return true if has that member $s->contains($m) # alias for has
if ($s->has($member)) { ... }
$s->member($m) # returns the member if has that member $s->element($m) # alias for member
$s->is_null # returns true if the set is empty $s->is_empty # alias for is_null $s->is_universal # returns true if the set is universal
$s->null # the null set $s->empty # alias for null $s->universe # the universe of the set
$u = $s->union($t); $i = $s->intersection($t); $d = $s->difference($t); $e = $s->symmetric_difference($t); $v = $s->unique($t); $c = $s->complement;
These methods have operator overloads:
$u = $s + $t; # union $i = $s * $t; # intersection $d = $s - $t; # difference $e = $s % $t; # symmetric_difference $v = $s / $t; # unique $c = -$s; # complement
Both the symmetric_difference
and unique
are symmetric on all
their arguments. For two sets they are identical but for more than
two sets beware: symmetric_difference
returns true for elements
that are in an odd number (1, 3, 5, ...) of sets, unique
returns
true for elements that are in one set.
Some examples of the various set differences:
set or difference value
$a (a b c d e) $b (c d e f g) $c (e f g h i)
$a->difference($b) (a b) $a->symmetric_difference($b) (a b f g) $a->unique($b) (a b f g)
$b->difference($a) (f g) $b->symmetric_difference($a) (a b f g) $b->unique($a) (a b f g)
$a->difference($b, $c) (a b) $a->symmetric_difference($b, $c) (a b e h i) $a->unique($b, $c) (a b h i)
$eq = $s->is_equal($t); $dj = $s->is_disjoint($t); $pi = $s->is_properly_intersecting($t); $ps = $s->is_proper_subset($t); $pS = $s->is_proper_superset($t); $is = $s->is_subset($t); $iS = $s->is_superset($t);
$cmp = $s->compare($t);
The compare
method returns a string from the following list:
``equal'', ``disjoint'', ``proper subset'', ``proper superset'', ``proper
intersect'', and in future (once I get around implementing it),
``disjoint universes''.
These methods have operator overloads:
$eq = $s == $t; # is_equal $dj = $s != $t; # is_disjoint # No operator overload for is_properly_intersecting. $ps = $s < $t; # is_proper_subset $pS = $s > $t; # is_proper_superset $is = $s <= $t; # is_subset $iS = $s >= $t; # is_superset
$cmp = $s <=> $t;
In Boolean contexts such as
if ($set) { ... } while ($set1 && $set2) { ... }
the size of the $set
is tested, so empty sets test as false,
and non-empty sets as true.
while (defined(my $e = $s->each)) { ... }
This is more memory-friendly than
for my $e ($s->elements) { ... }
which would first construct the full list of elements and then
walk through it: the $s->each
handles one element at a time.
Analogously to using normal each(%hash)
in scalar context,
using $s->each
has the following caveats:
undef
is returned. Since you may one
day have elements named 0
don't test just like this
while (my $e = $s->each) { ... } # WRONG
but instead like this
while (defined(my $e = $s->each)) { ... } # right
(An undef
as a set element doesn't really work, you get ""
.)
insert()
causes the iterator of the set being inserted (not the set being the
target of insertion) becoming reset. unique()
causes the iterators of
all the participant sets becoming reset. The iterator getting reset
most probably causes an endless loop. So avoid doing that.
If you want to customise the display routine you will have to
modify the as_string
callback. You can modify it either
for all sets by using as_string_callback()
as a class method:
my $class_callback = sub { ... };
Set::Scalar->as_string_callback($class_callback);
or for specific sets by using as_string_callback()
as an object
method:
my $callback = sub { ... };
$s1->as_string_callback($callback); $s2->as_string_callback($callback);
The anonymous subroutine gets as its first (and only) argument the
set to display as a string. For example to display the set $s
as a-b-c-d-e
instead of (a b c d e)
$s->as_string_callback(sub{join("-",sort $_[0]->elements)});
If called without an argument, the current callback is returned.
If called as a class method with undef as the only argument, the
original callback (the one returning (a b c d e)
) for all the sets
is restored, or if called for a single set the callback is removed
(and the callback for all the sets will be used).
The first priority of Set::Scalar is to be a convenient interface to sets. While not designed to be slow or big, neither has it been designed to be fast or compact.
Using references (or objects) as set members has not been extensively tested. The desired semantics are not always clear: what should happen when the elements behind the references change? Especially unclear is what should happen when the objects start having their own stringification overloads.
Set::Bag for bags (multisets, counted sets), and Bit::Vector for fast set operations (you have to take care of the element name to bit number and back mappings yourself), or Set::Infinite for sets of intervals, and many more. CPAN is your friend.
Jarkko Hietaniemi <jhi@iki.fi>
Copyright 2001,2002,2003,2004 by Jarkko Hietaniemi
This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
Set::Scalar - basic set operations |