NAME

Math::Combinatorics - Perform combinations and permutations on lists

SYNOPSIS

Available as an object oriented API.

use Math::Combinatorics;

my @n = qw(a b c);
my $combinat = Math::Combinatorics->new(count => 2,
                                        data => [@n],
                                       );

print "combinations of 2 from: ".join(" ",@n)."\n";
print "------------------------".("--" x scalar(@n))."\n";
while(my @combo = $combinat->next_combination){
  print join(' ', @combo)."\n";
}

print "\n";

print "permutations of 3 from: ".join(" ",@n)."\n";
print "------------------------".("--" x scalar(@n))."\n";
while(my @permu = $combinat->next_permutation){
  print join(' ', @permu)."\n";
}

output:

Or available via exported functions 'permute', 'combine', and 'factorial'.

use Math::Combinatorics;

my @n = qw(a b c);
print "combinations of 2 from: ".join(" ",@n)."\n";
print "------------------------".("--" x scalar(@n))."\n";
print join("\n", map { join " ", @$_ } combine(2,@n)),"\n";
print "\n";
print "permutations of 3 from: ".join(" ",@n)."\n";
print "------------------------".("--" x scalar(@n))."\n";
print join("\n", map { join " ", @$_ } permute(@n)),"\n";

Output:

combinations of 2 from: a b c
------------------------------
a b
a c
b c

permutations of 3 from: a b c
------------------------------
a b c
a c b
b a c
b c a
c a b
c b a

Output from both types of calls is the same, but the object-oriented approach consumes much less memory for large sets.

DESCRIPTION

Combinatorics is the branch of mathematics studying the enumeration, combination, and permutation of sets of elements and the mathematical relations that characterize their properties. As a jumping off point, refer to:

http://mathworld.wolfram.com/Combinatorics.html

This module provides a pure-perl implementation of nCk, nCRk, nPk, nPRk, !n and n! (combination, multiset, permutation, string, derangement, and factorial, respectively). Functional and object-oriented usages allow problems such as the following to be solved:

combine - nCk

http://mathworld.wolfram.com/Combination.html

"Fun questions to ask the pizza parlor wait staff: how many possible combinations of 2 toppings can I get on my pizza?".

derange - !n

http://mathworld.wolfram.com/Derangement.html

"A derangement of n ordered objects, denoted !n, is a permutation in which none of the objects appear in their "natural" (i.e., ordered) place."

permute - nPk

http://mathworld.wolfram.com/Permutation.html

"Master Mind Game: ways to arrange pieces of different colors in a certain number of positions, without repetition of a color".

Object-oriented usage additionally allows solving these problems by calling "new()" with a frequency vector:

string - nPRk

http://mathworld.wolfram.com/String.html

"Morse signals: diferent signals of 3 positions using the two symbols - and .".

$o = Math::Combinatorics->new( count=>3 , data=>[qw(. -)] , frequency=>[3,3] );
while ( my @x = $o->next_multiset ) {
  my $p = Math::Combinatorics->new( data=>\@x , frequency=>[map{1} @x] );
  while ( my @y = $p->next_string ) {
    #do something
  }
}

multiset/multichoose - nCRk

http://mathworld.wolfram.com/Multiset.html

"ways to extract 3 balls at once of a bag with 3 black and 3 white balls".

$o = Math::Combinatorics->new( count=>3 , data=>[qw(white black)] , frequency=>[3,3] );
while ( my @x = $o->next_multiset ) {
  #do something
}

EXPORT

the following export tags will bring a single method into the caller's namespace. no symbols are exported by default. see pod documentation below for method descriptions.

combine
derange
multiset
permute
string
factorial

AUTHOR

Allen Day <allenday@ucla.edu>, with algorithmic contributions from Christopher Eltschka and Tye.

ACKNOWLEDGEMENTS

A sincere thanks to everyone for helping to make this a better module. After initial development I've only had time to accept patches and improvements. Math::Combinatorics continues to be developed and improved by the community. Contributors of note include:

For adding new features: Carlos Rica, David Coppit, Carlos Segre, Lyon Lemmens

For bug reports: Ying Yang, Joerg Beyer, Marc Logghe, Yunheng Wang, Torsten Seemann, Gerrit Haase, Joern Behre, Lyon Lemmens, Federico Lucifredi

BUGS / TODO

Report them to the author.

* Need more extensive unit tests.

  * tests for new()'s frequency argment

* A known bug (more of a missing feature, actually) does not allow parameterization of k
for nPk in permute().  it is assumed k == n.  L</permute()> for details.  You can work
around this by making calls to both L</permute()> and L</combine()>

* Lots of really interesting stuff from Mathworld.Wolfram.com.  MathWorld rocks!  Expect
to see implementation of more concepts from their site, e.g.:

  http://mathworld.wolfram.com/BellNumber.html
  http://mathworld.wolfram.com/StirlingNumberoftheSecondKind.html
  http://mathworld.wolfram.com/Word.html

* Other combinatorics stuff
  http://en.wikipedia.org/wiki/Catalan_number
  http://en.wikipedia.org/wiki/Stirling_number

EXPORTED FUNCTIONS

combine()

Usage   : my @combinations = combine($k,@n);
Function: implements nCk (n choose k), or n!/(k!*(n-k!)).
          returns all unique unorderd combinations of k items from set n.
          items in n are assumed to be character data, and are
          copied into the return data structure (see "Returns" below).
Example : my @n = qw(a b c);
          my @c = combine(2,@n);
          print join "\n", map { join " ", @$_ } @c;
          # prints:
          # b c
          # a c
          # a b
Returns : a list of arrays, where each array contains a unique combination
          of k items from n
Args    : a list of items to be combined
Notes   : data is internally assumed to be alphanumeric.  this is necessary
          to efficiently generate combinations of large sets.  if you need
          combinations of non-alphanumeric data, or on data
          C<sort {$a cmp $b}> would not be appropriate, use the
          object-oriented API.  See L</new()> and the B<compare> option.

          Identical items are assumed to be non-unique.  That is, calling
          C<combine(1,'a','a') yields two sets: {a}, and {a}.  See
          L</next_multiset() if this is not the desired behavior.

derange()

Usage   : my @deranges = derange(@n);
Function: implements !n, a derangement of n items in which none of the
          items appear in their originally ordered place.
Example : my @n = qw(a b c);
          my @d = derange(@n);
          print join "\n", map { join " ", @$_ } @d;
          # prints:
          # a c b
          # b a c
          # b c a
          # c a b
          # c b a
Returns : a list of arrays, where each array contains a derangement of
          k items from n (where k == n).
Args    : a list of items to be deranged.
Note    : k should really be parameterizable.  this will happen
          in a later version of the module.  send me a patch to
          make that version come out sooner.
Notes   : data is internally assumed to be alphanumeric.  this is necessary
          to efficiently generate combinations of large sets.  if you need
          combinations of non-alphanumeric data, or on data
          C<sort {$a cmp $b}> would not be appropriate, use the
          object-oriented API.  See L</new()>, and the B<compare> option.

next_derangement()

Usage   : my @derangement = $c->next_derangement();
Function: get derangements for @data.
Returns : returns a permutation of items from @data (see L</new()>),
          where none of the items appear in their natural order.  repeated calls
          retrieve all unique derangements of @data elements.  a returned empty
          list signifies all derangements have been iterated.
Args    : none.

factorial()

Usage   : my $f = factorial(4); #returns 24, or 4*3*2*1
Function: calculates n! (n factorial).
Returns : undef if n is non-integer or n < 0
Args    : a positive, non-zero integer
Note    : this function is used internally by combine() and permute()

permute()

Usage   : my @permutations = permute(@n);
Function: implements nPk (n permute k) (where k == n), or n!/(n-k)!
           returns all unique permutations of k items from set n
          (where n == k, see "Note" below).  items in n are assumed to
          be character data, and are copied into the return data
          structure.
Example : my @n = qw(a b c);
          my @p = permute(@n);
          print join "\n", map { join " ", @$_ } @p;
          # prints:
          # b a c
          # b c a
          # c b a
          # c a b
          # a c b
          # a b c
Returns : a list of arrays, where each array contains a permutation of
          k items from n (where k == n).
Args    : a list of items to be permuted.
Note    : k should really be parameterizable.  this will happen
          in a later version of the module.  send me a patch to
          make that version come out sooner.
Notes   : data is internally assumed to be alphanumeric.  this is necessary
          to efficiently generate combinations of large sets.  if you need
          combinations of non-alphanumeric data, or on data
          C<sort {$a cmp $b}> would not be appropriate, use the
          object-oriented API.  See L</new()>, and the B<compare> option.

          Identical items are assumed to be non-unique.  That is, calling
          C<permute('a','a') yields two sets: {a,a}, and {a,a}.  See
          L</next_string() if this is not the desired behavior.

CONSTRUCTOR

new()

Usage   : my $c = Math::Combinatorics->new( count => 2,       #treated as int
                                            data => [1,2,3,4] #arrayref or anonymous array
                                          );
Function: build a new Math::Combinatorics object.
Returns : a Math::Combinatorics object
Args    : count     - required for combinatoric functions/methods.  number of elements to be
                      present in returned set(s).
          data      - required for combinatoric B<AND> permutagenic functions/methods.  this is the
                      set elements are chosen from.  B<NOTE>: this array is modified in place; make
                      a copy of your array if the order matters in the caller's space.
          frequency - optional vector of data frequencies.  must be the same length as the B<data>
                      constructor argument.  These two constructor calls here are equivalent:

                        $a = 'a';
                        $b = 'b';

                        Math::Combinatorics->new( count=>2, data=>[\$a,\$a,\$a,\$a,\$a,\$b,\$b] );
                        Math::Combinatorics->new( count=>2, data=>[\$a,\$b], frequency=>[5,2] );

                      so why use this?  sometimes it's useful to have multiple identical entities in
                      a set (in set theory jargon, this is called a "bag", See L<Set::Bag>).
          compare   - optional subroutine reference used in sorting elements of the set.  examples:

                      #appropriate for character elements
                      compare => sub { $_[0] cmp $_[1] }
                      #appropriate for numeric elements
                      compare => sub { $_[0] <=> $_[1] }
                      #appropriate for object elements, perhaps
                      compare => sub { $_[0]->value <=> $_[1]->value }

                    The default sort mechanism is based on references, and cannot be predicted.
                    Improvements for a more flexible compare() mechanism are most welcome.

OBJECT METHODS

next_combination()

Usage   : my @combo = $c->next_combination();
Function: get combinations of size $count from @data.
Returns : returns a combination of $count items from @data (see L</new()>).
          repeated calls retrieve all unique combinations of $count elements.
          a returned empty list signifies all combinations have been iterated.
Note    : this method may only be used if a B<frequency> argument is B<NOT>
          given to L</new()>, otherwise use L</next_multiset()>.
Args    : none.

next_multiset()

Usage   : my @multiset = $c->next_multiset();
Function: get multisets for @data.
Returns : returns a multiset of items from @data (see L</new()>).
          a multiset is a special type of combination where the set from which
          combinations are drawn contains items that are indistinguishable.  use
          L</next_multiset()> when a B<frequency> argument is passed to L</new()>.
          repeated calls retrieve all unique multisets of @data elements.  a
          returned empty list signifies all multisets have been iterated.
Note    : this method may only be used if a B<frequency> argument is given to
          L</new()>, otherwise use L</next_combination()>.
Args    : none.

next_permutation()

Usage   : my @permu = $c->next_permutation();
Function: get permutations of elements in @data.
Returns : returns a permutation of items from @data (see L</new()>).
          repeated calls retrieve all unique permutations of @data elements.
          a returned empty list signifies all permutations have been iterated.
Note    : this method may only be used if a B<frequency> argument is B<NOT>
          given to L</new()>, otherwise use L</next_string()>.
Args    : none.

next_string()

Usage   : my @string = $c->next_string();
Function: get strings for @data.
Returns : returns a multiset of items from @data (see L</new()>).
          a multiset is a special type of permutation where the set from which
          combinations are drawn contains items that are indistinguishable.  use
          L</next_permutation()> when a B<frequency> argument is passed to L</new()>.
          repeated calls retrieve all unique multisets of @data elements.  a
          returned empty list signifies all strings have been iterated.
Note    : this method may only be used if a B<frequency> argument is given to
          L</new()>, otherwise use L</next_permutation()>.
Args    : none.

INTERNAL FUNCTIONS AND METHODS

sum()

Usage   : my $sum = sum(1,2,3); # returns 6
Function: sums a list of integers.  non-integer list elements are ignored
Returns : sum of integer items in arguments passed in
Args    : a list of integers
Note    : this function is used internally by combine()

compare()

Usage   : $obj->compare()
Function: internal, undocumented.  holds a comparison coderef.
Returns : value of compare (a coderef)

count()

Usage   : $obj->count()
Function: internal, undocumented.  holds the "k" in nCk or nPk.
Returns : value of count (an int)

data()

Usage   : $obj->data()
Function: internal, undocumented.  holds the set "n" in nCk or nPk.
Returns : value of data (an arrayref)

swap()

internal, undocumented.

reverse()

internal, undocumented.

rotate()

internal, undocumented.

upper_bound()

internal, undocumented.

lower_bound()

internal, undocumented.

_permutation_cursor()

Usage   : $obj->_permutation_cursor()
Function: internal method.  cursor on permutation iterator order.
Returns : value of _permutation_cursor (an arrayref)
Args    : none

To install Math::Combinatorics, copy and paste the appropriate command in to your terminal.

cpanm

cpanm Math::Combinatorics

CPAN shell

perl -MCPAN -e shell
install Math::Combinatorics

For more information on module installation, please visit the detailed CPAN module installation guide.

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NAME

SYNOPSIS

DESCRIPTION

EXPORT

AUTHOR

ACKNOWLEDGEMENTS

BUGS / TODO

SEE ALSO

EXPORTED FUNCTIONS

combine()

derange()

next_derangement()

factorial()

permute()

CONSTRUCTOR

new()

OBJECT METHODS

next_combination()

next_multiset()

next_permutation()

next_string()

INTERNAL FUNCTIONS AND METHODS

sum()

compare()

count()

data()

swap()

reverse()

rotate()

upper_bound()

lower_bound()

_permutation_cursor()

Module Install Instructions