Provided by: liblist-compare-perl_0.55-2_all 
NAME
List::Compare - Compare elements of two or more lists
VERSION
This document refers to version 0.55 of List::Compare. This version was released August
16 2020.
SYNOPSIS
The bare essentials:
@Llist = qw(abel abel baker camera delta edward fargo golfer);
@Rlist = qw(baker camera delta delta edward fargo golfer hilton);
$lc = List::Compare->new(\@Llist, \@Rlist);
@intersection = $lc->get_intersection;
@union = $lc->get_union;
... and so forth.
DISCUSSION: Modes and Methods
Regular Case: Compare Two Lists
• Constructor: "new()"
Create a List::Compare object. Put the two lists into arrays (named or anonymous) and
pass references to the arrays to the constructor.
@Llist = qw(abel abel baker camera delta edward fargo golfer);
@Rlist = qw(baker camera delta delta edward fargo golfer hilton);
$lc = List::Compare->new(\@Llist, \@Rlist);
By default, List::Compare's methods return lists which are sorted using Perl's default
"sort" mode: ASCII-betical sorting. Should you not need to have these lists sorted,
you may achieve a speed boost by constructing the List::Compare object with the
unsorted option:
$lc = List::Compare->new('-u', \@Llist, \@Rlist);
or
$lc = List::Compare->new('--unsorted', \@Llist, \@Rlist);
• Alternative Constructor
If you prefer a more explicit delineation of the types of arguments passed to a
function, you may use this 'single hashref' kind of constructor to build a
List::Compare object:
$lc = List::Compare->new( { lists => [\@Llist, \@Rlist] } );
or
$lc = List::Compare->new( {
lists => [\@Llist, \@Rlist],
unsorted => 1,
} );
• "get_intersection()"
Get those items which appear at least once in both lists (their intersection).
@intersection = $lc->get_intersection;
• "get_union()"
Get those items which appear at least once in either list (their union).
@union = $lc->get_union;
• "get_unique()"
Get those items which appear (at least once) only in the first list.
@Lonly = $lc->get_unique;
@Lonly = $lc->get_Lonly; # alias
• "get_complement()"
Get those items which appear (at least once) only in the second list.
@Ronly = $lc->get_complement;
@Ronly = $lc->get_Ronly; # alias
• "get_symmetric_difference()"
Get those items which appear at least once in either the first or the second list, but
not both.
@LorRonly = $lc->get_symmetric_difference;
@LorRonly = $lc->get_symdiff; # alias
@LorRonly = $lc->get_LorRonly; # alias
• "get_bag()"
Make a bag of all those items in both lists. The bag differs from the union of the
two lists in that it holds as many copies of individual elements as appear in the
original lists.
@bag = $lc->get_bag;
• Return references rather than lists
An alternative approach to the above methods: If you do not immediately require an
array as the return value of the method call, but simply need a reference to an
(anonymous) array, use one of the following parallel methods:
$intersection_ref = $lc->get_intersection_ref;
$union_ref = $lc->get_union_ref;
$Lonly_ref = $lc->get_unique_ref;
$Lonly_ref = $lc->get_Lonly_ref; # alias
$Ronly_ref = $lc->get_complement_ref;
$Ronly_ref = $lc->get_Ronly_ref; # alias
$LorRonly_ref = $lc->get_symmetric_difference_ref;
$LorRonly_ref = $lc->get_symdiff_ref; # alias
$LorRonly_ref = $lc->get_LorRonly_ref; # alias
$bag_ref = $lc->get_bag_ref;
• "is_LsubsetR()"
Return a true value if the first argument passed to the constructor ('L' for 'left')
is a subset of the second argument passed to the constructor ('R' for 'right').
$LR = $lc->is_LsubsetR;
Return a true value if R is a subset of L.
$RL = $lc->is_RsubsetL;
• "is_LequivalentR()"
Return a true value if the two lists passed to the constructor are equivalent, i.e. if
every element in the left-hand list ('L') appears at least once in the right-hand list
('R') and vice versa.
$eqv = $lc->is_LequivalentR;
$eqv = $lc->is_LeqvlntR; # alias
• "is_LdisjointR()"
Return a true value if the two lists passed to the constructor are disjoint, i.e. if
the two lists have zero elements in common (or, what is the same thing, if their
intersection is an empty set).
$disj = $lc->is_LdisjointR;
• "print_subset_chart()"
Pretty-print a chart showing whether one list is a subset of the other.
$lc->print_subset_chart;
• "print_equivalence_chart()"
Pretty-print a chart showing whether the two lists are equivalent (same elements found
at least once in both).
$lc->print_equivalence_chart;
• "is_member_which()"
Determine in which (if any) of the lists passed to the constructor a given string can
be found. In list context, return a list of those indices in the constructor's
argument list corresponding to lists holding the string being tested.
@memb_arr = $lc->is_member_which('abel');
In the example above, @memb_arr will be:
( 0 )
because 'abel' is found only in @Al which holds position 0 in the list of arguments
passed to "new()".
In scalar context, the return value is the number of lists passed to the constructor
in which a given string is found.
As with other List::Compare methods which return a list, you may wish the above method
returned a (scalar) reference to an array holding the list:
$memb_arr_ref = $lc->is_member_which_ref('baker');
In the example above, $memb_arr_ref will be:
[ 0, 1 ]
because 'baker' is found in @Llist and @Rlist, which hold positions 0 and 1,
respectively, in the list of arguments passed to "new()".
Note: methods "is_member_which()" and "is_member_which_ref" test only one string at a
time and hence take only one argument. To test more than one string at a time see the
next method, "are_members_which()".
• "are_members_which()"
Determine in which (if any) of the lists passed to the constructor one or more given
strings can be found. The strings to be tested are placed in an array (named or
anonymous); a reference to that array is passed to the method.
$memb_hash_ref =
$lc->are_members_which([ qw| abel baker fargo hilton zebra | ]);
Note: In versions of List::Compare prior to 0.25 (April 2004), the strings to be
tested could be passed as a flat list. This is no longer possible; the argument must
now be a reference to an array.
The return value is a reference to a hash of arrays. The key for each element in this
hash is the string being tested. Each element's value is a reference to an anonymous
array whose elements are those indices in the constructor's argument list
corresponding to lists holding the strings being tested. In the examples above,
$memb_hash_ref will be:
{
abel => [ 0 ],
baker => [ 0, 1 ],
fargo => [ 0, 1 ],
hilton => [ 1 ],
zebra => [ ],
};
Note: "are_members_which()" can take more than one argument; "is_member_which()" and
"is_member_which_ref()" each take only one argument. Unlike those two methods,
"are_members_which()" returns a hash reference.
• "is_member_any()"
Determine whether a given string can be found in any of the lists passed as arguments
to the constructor. Return 1 if a specified string can be found in any of the lists
and 0 if not.
$found = $lc->is_member_any('abel');
In the example above, $found will be 1 because 'abel' is found in one or more of the
lists passed as arguments to "new()".
• "are_members_any()"
Determine whether a specified string or strings can be found in any of the lists
passed as arguments to the constructor. The strings to be tested are placed in an
array (named or anonymous); a reference to that array is passed to "are_members_any".
$memb_hash_ref = $lc->are_members_any([ qw| abel baker fargo hilton zebra | ]);
Note: In versions of List::Compare prior to 0.25 (April 2004), the strings to be
tested could be passed as a flat list. This is no longer possible; the argument must
now be a reference to an array.
The return value is a reference to a hash where an element's key is the string being
tested and the element's value is 1 if the string can be found in any of the lists and
0 if not. In the examples above, $memb_hash_ref will be:
{
abel => 1,
baker => 1,
fargo => 1,
hilton => 1,
zebra => 0,
};
"zebra"'s value is 0 because "zebra" is not found in either of the lists passed as
arguments to "new()".
• "get_version()"
Return current List::Compare version number.
$vers = $lc->get_version;
Accelerated Case: When User Only Wants a Single Comparison
• Constructor "new()"
If you are certain that you will only want the results of a single comparison,
computation may be accelerated by passing '-a' or "'--accelerated" as the first
argument to the constructor.
@Llist = qw(abel abel baker camera delta edward fargo golfer);
@Rlist = qw(baker camera delta delta edward fargo golfer hilton);
$lca = List::Compare->new('-a', \@Llist, \@Rlist);
or
$lca = List::Compare->new('--accelerated', \@Llist, \@Rlist);
As with List::Compare's Regular case, should you not need to have a sorted list
returned by an accelerated List::Compare method, you may achieve a speed boost by
constructing the accelerated List::Compare object with the unsorted option:
$lca = List::Compare->new('-u', '-a', \@Llist, \@Rlist);
or
$lca = List::Compare->new('--unsorted', '--accelerated', \@Llist, \@Rlist);
• Alternative Constructor
You may use the 'single hashref' constructor format to build a List::Compare object
calling for the Accelerated mode:
$lca = List::Compare->new( {
lists => [\@Llist, \@Rlist],
accelerated => 1,
} );
or
$lca = List::Compare->new( {
lists => [\@Llist, \@Rlist],
accelerated => 1,
unsorted => 1,
} );
• Methods
All the comparison methods available in the Regular case are available to you in the
Accelerated case as well.
@intersection = $lca->get_intersection;
@union = $lca->get_union;
@Lonly = $lca->get_unique;
@Ronly = $lca->get_complement;
@LorRonly = $lca->get_symmetric_difference;
@bag = $lca->get_bag;
$intersection_ref = $lca->get_intersection_ref;
$union_ref = $lca->get_union_ref;
$Lonly_ref = $lca->get_unique_ref;
$Ronly_ref = $lca->get_complement_ref;
$LorRonly_ref = $lca->get_symmetric_difference_ref;
$bag_ref = $lca->get_bag_ref;
$LR = $lca->is_LsubsetR;
$RL = $lca->is_RsubsetL;
$eqv = $lca->is_LequivalentR;
$disj = $lca->is_LdisjointR;
$lca->print_subset_chart;
$lca->print_equivalence_chart;
@memb_arr = $lca->is_member_which('abel');
$memb_arr_ref = $lca->is_member_which_ref('baker');
$memb_hash_ref = $lca->are_members_which(
[ qw| abel baker fargo hilton zebra | ]);
$found = $lca->is_member_any('abel');
$memb_hash_ref = $lca->are_members_any(
[ qw| abel baker fargo hilton zebra | ]);
$vers = $lca->get_version;
All the aliases for methods available in the Regular case are available to you in the
Accelerated case as well.
Multiple Case: Compare Three or More Lists
• Constructor "new()"
Create a List::Compare object. Put each list into an array and pass references to the
arrays to the constructor.
@Al = qw(abel abel baker camera delta edward fargo golfer);
@Bob = qw(baker camera delta delta edward fargo golfer hilton);
@Carmen = qw(fargo golfer hilton icon icon jerky kappa);
@Don = qw(fargo icon jerky);
@Ed = qw(fargo icon icon jerky);
$lcm = List::Compare->new(\@Al, \@Bob, \@Carmen, \@Don, \@Ed);
As with List::Compare's Regular case, should you not need to have a sorted list
returned by a List::Compare method, you may achieve a speed boost by constructing the
object with the unsorted option:
$lcm = List::Compare->new('-u', \@Al, \@Bob, \@Carmen, \@Don, \@Ed);
or
$lcm = List::Compare->new('--unsorted', \@Al, \@Bob, \@Carmen, \@Don, \@Ed);
• Alternative Constructor
You may use the 'single hashref' constructor format to build a List::Compare object to
process three or more lists at once:
$lcm = List::Compare->new( {
lists => [\@Al, \@Bob, \@Carmen, \@Don, \@Ed],
} );
or
$lcm = List::Compare->new( {
lists => [\@Al, \@Bob, \@Carmen, \@Don, \@Ed],
unsorted => 1,
} );
• Multiple Mode Methods Analogous to Regular and Accelerated Mode Methods
Each List::Compare method available in the Regular and Accelerated cases has an
analogue in the Multiple case. However, the results produced usually require more
careful specification.
Note: Certain of the following methods available in List::Compare's Multiple mode
take optional numerical arguments where those numbers represent the index position of
a particular list in the list of arguments passed to the constructor. To specify this
index position correctly,
• start the count at 0 (as is customary with Perl array indices); and
• do not count any unsorted option ('-u' or '--unsorted') preceding the array
references in the constructor's own argument list.
Example:
$lcmex = List::Compare->new('--unsorted', \@alpha, \@beta, \@gamma);
For the purpose of supplying a numerical argument to a method which optionally takes
such an argument, '--unsorted' is skipped, @alpha is 0, @beta is 1, and so forth.
• "get_intersection()"
Get those items found in each of the lists passed to the constructor (their
intersection):
@intersection = $lcm->get_intersection;
• "get_union()"
Get those items found in any of the lists passed to the constructor (their union):
@union = $lcm->get_union;
• "get_unique()"
To get those items which appear only in one particular list, provide
"get_unique()" with that list's index position in the list of arguments passed to
the constructor (not counting any '-u' or '--unsorted' option).
Example: @Carmen has index position 2 in the constructor's @_. To get elements
unique to @Carmen:
@Lonly = $lcm->get_unique(2);
If no index position is passed to "get_unique()" it will default to 0 and report
items unique to the first list passed to the constructor.
• "get_complement()"
To get those items which appear in any list other than one particular list,
provide "get_complement()" with that list's index position in the list of
arguments passed to the constructor (not counting any '-u' or '--unsorted'
option).
Example: @Don has index position 3 in the constructor's @_. To get elements not
found in @Don:
@Ronly = $lcm->get_complement(3);
If no index position is passed to "get_complement()" it will default to 0 and
report items found in any list other than the first list passed to the
constructor.
• "get_symmetric_difference()"
Get those items each of which appears in only one of the lists passed to the
constructor (their symmetric_difference);
@LorRonly = $lcm->get_symmetric_difference;
• "get_bag()"
Make a bag of all items found in any list. The bag differs from the lists' union
in that it holds as many copies of individual elements as appear in the original
lists.
@bag = $lcm->get_bag;
• Return reference instead of list
An alternative approach to the above methods: If you do not immediately require
an array as the return value of the method call, but simply need a reference to an
array, use one of the following parallel methods:
$intersection_ref = $lcm->get_intersection_ref;
$union_ref = $lcm->get_union_ref;
$Lonly_ref = $lcm->get_unique_ref(2);
$Ronly_ref = $lcm->get_complement_ref(3);
$LorRonly_ref = $lcm->get_symmetric_difference_ref;
$bag_ref = $lcm->get_bag_ref;
• "is_LsubsetR()"
To determine whether one particular list is a subset of another list passed to the
constructor, provide "is_LsubsetR()" with the index position of the presumed
subset (ignoring any unsorted option), followed by the index position of the
presumed superset.
Example: To determine whether @Ed is a subset of @Carmen, call:
$LR = $lcm->is_LsubsetR(4,2);
A true value (1) is returned if the left-hand list is a subset of the right-hand
list; a false value (0) is returned otherwise.
If no arguments are passed, "is_LsubsetR()" defaults to "(0,1)" and compares the
first two lists passed to the constructor.
• "is_LequivalentR()"
To determine whether any two particular lists are equivalent to each other,
provide "is_LequivalentR" with their index positions in the list of arguments
passed to the constructor (ignoring any unsorted option).
Example: To determine whether @Don and @Ed are equivalent, call:
$eqv = $lcm->is_LequivalentR(3,4);
A true value (1) is returned if the lists are equivalent; a false value (0)
otherwise.
If no arguments are passed, "is_LequivalentR" defaults to "(0,1)" and compares the
first two lists passed to the constructor.
• "is_LdisjointR()"
To determine whether any two particular lists are disjoint from each other (i.e.,
have no members in common), provide "is_LdisjointR" with their index positions in
the list of arguments passed to the constructor (ignoring any unsorted option).
Example: To determine whether @Don and @Ed are disjoint, call:
$disj = $lcm->is_LdisjointR(3,4);
A true value (1) is returned if the lists are equivalent; a false value (0)
otherwise.
If no arguments are passed, "is_LdisjointR" defaults to "(0,1)" and compares the
first two lists passed to the constructor.
• "print_subset_chart()"
Pretty-print a chart showing the subset relationships among the various source
lists:
$lcm->print_subset_chart;
• "print_equivalence_chart()"
Pretty-print a chart showing the equivalence relationships among the various
source lists:
$lcm->print_equivalence_chart;
• "is_member_which()"
Determine in which (if any) of the lists passed to the constructor a given string
can be found. In list context, return a list of those indices in the
constructor's argument list (ignoring any unsorted option) corresponding to i
lists holding the string being tested.
@memb_arr = $lcm->is_member_which('abel');
In the example above, @memb_arr will be:
( 0 )
because 'abel' is found only in @Al which holds position 0 in the list of
arguments passed to "new()".
• "is_member_which_ref()"
As with other List::Compare methods which return a list, you may wish the above
method returned a (scalar) reference to an array holding the list:
$memb_arr_ref = $lcm->is_member_which_ref('jerky');
In the example above, $memb_arr_ref will be:
[ 3, 4 ]
because 'jerky' is found in @Don and @Ed, which hold positions 3 and 4,
respectively, in the list of arguments passed to "new()".
Note: methods "is_member_which()" and "is_member_which_ref" test only one string
at a time and hence take only one argument. To test more than one string at a
time see the next method, "are_members_which()".
• "are_members_which()"
Determine in "which" (if any) of the lists passed to the constructor one or more
given strings can be found. The strings to be tested are placed in an anonymous
array, a reference to which is passed to the method.
$memb_hash_ref =
$lcm->are_members_which([ qw| abel baker fargo hilton zebra | ]);
Note: In versions of List::Compare prior to 0.25 (April 2004), the strings to be
tested could be passed as a flat list. This is no longer possible; the argument
must now be a reference to an anonymous array.
The return value is a reference to a hash of arrays. The key for each element in
this hash is the string being tested. Each element's value is a reference to an
anonymous array whose elements are those indices in the constructor's argument
list corresponding to lists holding the strings being tested.
In the two examples above, $memb_hash_ref will be:
{
abel => [ 0 ],
baker => [ 0, 1 ],
fargo => [ 0, 1, 2, 3, 4 ],
hilton => [ 1, 2 ],
zebra => [ ],
};
Note: "are_members_which()" can take more than one argument; "is_member_which()"
and "is_member_which_ref()" each take only one argument. "are_members_which()"
returns a hash reference; the other methods return either a list or a reference to
an array holding that list, depending on context.
• "is_member_any()"
Determine whether a given string can be found in any of the lists passed as
arguments to the constructor.
$found = $lcm->is_member_any('abel');
Return 1 if a specified string can be found in any of the lists and 0 if not.
In the example above, $found will be 1 because 'abel' is found in one or more of
the lists passed as arguments to "new()".
• "are_members_any()"
Determine whether a specified string or strings can be found in any of the lists
passed as arguments to the constructor. The strings to be tested are placed in an
array (anonymous or named), a reference to which is passed to the method.
$memb_hash_ref = $lcm->are_members_any([ qw| abel baker fargo hilton zebra | ]);
Note: In versions of List::Compare prior to 0.25 (April 2004), the strings to be
tested could be passed as a flat list. This is no longer possible; the argument
must now be a reference to an anonymous array.
The return value is a reference to a hash where an element's key is the string
being tested and the element's value is 1 if the string can be found in "any" of
the lists and 0 if not. In the two examples above, $memb_hash_ref will be:
{
abel => 1,
baker => 1,
fargo => 1,
hilton => 1,
zebra => 0,
};
"zebra"'s value will be 0 because "zebra" is not found in any of the lists passed
as arguments to "new()".
• "get_version()"
Return current List::Compare version number:
$vers = $lcm->get_version;
• Multiple Mode Methods Not Analogous to Regular and Accelerated Mode Methods
• "get_nonintersection()"
Get those items found in any of the lists passed to the constructor which do not
appear in all of the lists (i.e., all items except those found in the intersection
of the lists):
@nonintersection = $lcm->get_nonintersection;
• "get_shared()"
Get those items which appear in more than one of the lists passed to the
constructor (i.e., all items except those found in their symmetric difference);
@shared = $lcm->get_shared;
• "get_nonintersection_ref()"
If you only need a reference to an array as a return value rather than a full
array, use the following alternative methods:
$nonintersection_ref = $lcm->get_nonintersection_ref;
$shared_ref = $lcm->get_shared_ref;
• "get_unique_all()"
Get a reference to an array of array references where each of the interior arrays
holds the list of those items unique to the list passed to the constructor with
the same index position.
$unique_all_ref = $lcm->get_unique_all();
In the example above, $unique_all_ref will hold:
[
[ qw| abel | ],
[ ],
[ qw| jerky | ],
[ ],
[ ],
]
• "get_complement_all()"
Get a reference to an array of array references where each of the interior arrays
holds the list of those items in the complement to the list passed to the
constructor with the same index position.
$complement_all_ref = $lcm->get_complement_all();
In the example above, $complement_all_ref will hold:
[
[ qw| hilton icon jerky | ],
[ qw| abel icon jerky | ],
[ qw| abel baker camera delta edward | ],
[ qw| abel baker camera delta edward jerky | ],
[ qw| abel baker camera delta edward jerky | ],
]
Multiple Accelerated Case: Compare Three or More Lists but Request Only a Single Comparison
among the Lists
• Constructor "new()"
If you are certain that you will only want the results of a single comparison among
three or more lists, computation may be accelerated by passing '-a' or
"'--accelerated" as the first argument to the constructor.
@Al = qw(abel abel baker camera delta edward fargo golfer);
@Bob = qw(baker camera delta delta edward fargo golfer hilton);
@Carmen = qw(fargo golfer hilton icon icon jerky kappa);
@Don = qw(fargo icon jerky);
@Ed = qw(fargo icon icon jerky);
$lcma = List::Compare->new('-a',
\@Al, \@Bob, \@Carmen, \@Don, \@Ed);
As with List::Compare's other cases, should you not need to have a sorted list
returned by a List::Compare method, you may achieve a speed boost by constructing the
object with the unsorted option:
$lcma = List::Compare->new('-u', '-a',
\@Al, \@Bob, \@Carmen, \@Don, \@Ed);
or
$lcma = List::Compare->new('--unsorted', '--accelerated',
\@Al, \@Bob, \@Carmen, \@Don, \@Ed);
As was the case with List::Compare's Multiple mode, do not count the unsorted option
('-u' or '--unsorted') or the accelerated option ('-a' or '--accelerated') when
determining the index position of a particular list in the list of array references
passed to the constructor.
Example:
$lcmaex = List::Compare->new('--unsorted', '--accelerated',
\@alpha, \@beta, \@gamma);
• Alternative Constructor
The 'single hashref' format may be used to construct a List::Compare object which
calls for accelerated processing of three or more lists at once:
$lcmaex = List::Compare->new( {
accelerated => 1,
lists => [\@alpha, \@beta, \@gamma],
} );
or
$lcmaex = List::Compare->new( {
unsorted => 1,
accelerated => 1,
lists => [\@alpha, \@beta, \@gamma],
} );
• Methods
For the purpose of supplying a numerical argument to a method which optionally takes
such an argument, '--unsorted' and "'--accelerated" are skipped, @alpha is 0, @beta is
1, and so forth. To get a list of those items unique to @gamma, you would call:
@gamma_only = $lcmaex->get_unique(2);
Passing Seen-hashes to the Constructor Instead of Arrays
• When Seen-Hashes Are Already Available to You
Suppose that in a particular Perl program, you had to do extensive munging of data
from an external source and that, once you had correctly parsed a line of data, it was
easier to assign that datum to a hash than to an array. More specifically, suppose
that you used each datum as the key to an element of a lookup table in the form of a
seen-hash:
my %Llist = (
abel => 2,
baker => 1,
camera => 1,
delta => 1,
edward => 1,
fargo => 1,
golfer => 1,
);
my %Rlist = (
baker => 1,
camera => 1,
delta => 2,
edward => 1,
fargo => 1,
golfer => 1,
hilton => 1,
);
In other words, suppose it was more convenient to compute a lookup table implying a
list than to compute that list explicitly.
Since in almost all cases List::Compare takes the elements in the arrays passed to its
constructor and internally assigns them to elements in a seen-hash, why shouldn't you
be able to pass (references to) seen-hashes directly to the constructor and avoid
unnecessary array assignments before the constructor is called?
• Constructor "new()"
You can now do so:
$lcsh = List::Compare->new(\%Llist, \%Rlist);
• Methods
All of List::Compare's output methods are supported without further modification when
references to seen-hashes are passed to the constructor.
@intersection = $lcsh->get_intersection;
@union = $lcsh->get_union;
@Lonly = $lcsh->get_unique;
@Ronly = $lcsh->get_complement;
@LorRonly = $lcsh->get_symmetric_difference;
@bag = $lcsh->get_bag;
$intersection_ref = $lcsh->get_intersection_ref;
$union_ref = $lcsh->get_union_ref;
$Lonly_ref = $lcsh->get_unique_ref;
$Ronly_ref = $lcsh->get_complement_ref;
$LorRonly_ref = $lcsh->get_symmetric_difference_ref;
$bag_ref = $lcsh->get_bag_ref;
$LR = $lcsh->is_LsubsetR;
$RL = $lcsh->is_RsubsetL;
$eqv = $lcsh->is_LequivalentR;
$disj = $lcsh->is_LdisjointR;
$lcsh->print_subset_chart;
$lcsh->print_equivalence_chart;
@memb_arr = $lsch->is_member_which('abel');
$memb_arr_ref = $lsch->is_member_which_ref('baker');
$memb_hash_ref = $lsch->are_members_which(
[ qw| abel baker fargo hilton zebra | ]);
$found = $lsch->is_member_any('abel');
$memb_hash_ref = $lsch->are_members_any(
[ qw| abel baker fargo hilton zebra | ]);
$vers = $lcsh->get_version;
$unique_all_ref = $lcsh->get_unique_all();
$complement_all_ref = $lcsh->get_complement_all();
• Accelerated Mode and Seen-Hashes
To accelerate processing when you want only a single comparison among two or more
lists, you can pass '-a' or "'--accelerated" to the constructor before passing
references to seen-hashes.
$lcsha = List::Compare->new('-a', \%Llist, \%Rlist);
To compare three or more lists simultaneously, pass three or more references to seen-
hashes. Thus,
$lcshm = List::Compare->new(\%Alpha, \%Beta, \%Gamma);
will generate meaningful comparisons of three or more lists simultaneously.
• Unsorted Results and Seen-Hashes
If you do not need sorted lists returned, pass '-u' or "--unsorted" to the constructor
before passing references to seen-hashes.
$lcshu = List::Compare->new('-u', \%Llist, \%Rlist);
$lcshau = List::Compare->new('-u', '-a', \%Llist, \%Rlist);
$lcshmu = List::Compare->new('--unsorted', \%Alpha, \%Beta, \%Gamma);
As was true when we were using List::Compare's Multiple and Multiple Accelerated
modes, do not count any unsorted or accelerated option when determining the array
index of a particular seen-hash reference passed to the constructor.
• Alternative Constructor
The 'single hashref' form of constructor is also available to build List::Compare
objects where seen-hashes are used as arguments:
$lcshu = List::Compare->new( {
unsorted => 1,
lists => [\%Llist, \%Rlist],
} );
$lcshau = List::Compare->new( {
unsorted => 1,
accelerated => 1,
lists => [\%Llist, \%Rlist],
} );
$lcshmu = List::Compare->new( {
unsorted => 1,
lists => [\%Alpha, \%Beta, \%Gamma],
} );
DISCUSSION: Principles
General Comments
List::Compare is an object-oriented implementation of very common Perl code (see "History,
References and Development" below) used to determine interesting relationships between two
or more lists at a time. A List::Compare object is created and automatically computes the
values needed to supply List::Compare methods with appropriate results. In the current
implementation List::Compare methods will return new lists containing the items found in
any designated list alone (unique), any list other than a designated list (complement),
the intersection and union of all lists and so forth. List::Compare also has (a) methods
to return Boolean values indicating whether one list is a subset of another and whether
any two lists are equivalent to each other (b) methods to pretty-print very simple charts
displaying the subset and equivalence relationships among lists.
Except for List::Compare's "get_bag()" method, multiple instances of an element in a given
list count only once with respect to computing the intersection, union, etc. of the two
lists. In particular, List::Compare considers two lists as equivalent if each element of
the first list can be found in the second list and vice versa. 'Equivalence' in this
usage takes no note of the frequency with which elements occur in either list or their
order within the lists. List::Compare asks the question: Did I see this item in this
list at all? Only when you use "List::Compare::get_bag()" to compute a bag holding the
two lists do you ask the question: How many times did this item occur in this list?
List::Compare Modes
In its current implementation List::Compare has four modes of operation.
• Regular Mode
List::Compare's Regular mode is based on List::Compare v0.11 -- the first version of
List::Compare released to CPAN (June 2002). It compares only two lists at a time.
Internally, its initializer does all computations needed to report any desired
comparison and its constructor stores the results of these computations. Its public
methods merely report these results.
This approach has the advantage that if you need to examine more than one form of
comparison between two lists (e.g., the union, intersection and symmetric difference
of two lists), the comparisons are pre-calculated. This approach is efficient because
certain types of comparison presuppose that other types have already been calculated.
For example, to calculate the symmetric difference of two lists, one must first
determine the items unique to each of the two lists.
• Accelerated Mode
The current implementation of List::Compare offers you the option of getting even
faster results provided that you only need the result from a single form of comparison
between two lists. (e.g., only the union -- nothing else). In the Accelerated mode,
List::Compare's initializer does no computation and its constructor stores only
references to the two source lists. All computation needed to report results is
deferred to the method calls.
The user selects this approach by passing the option flag '-a' to the constructor
before passing references to the two source lists. List::Compare notes the option
flag and silently switches into Accelerated mode. From the perspective of the user,
there is no further difference in the code or in the results.
Benchmarking suggests that List::Compare's Accelerated mode (a) is faster than its
Regular mode when only one comparison is requested; (b) is about as fast as Regular
mode when two comparisons are requested; and (c) becomes considerably slower than
Regular mode as each additional comparison above two is requested.
• Multiple Mode
List::Compare now offers the possibility of comparing three or more lists at a time.
Simply store the extra lists in arrays and pass references to those arrays to the
constructor. List::Compare detects that more than two lists have been passed to the
constructor and silently switches into Multiple mode.
As described in the Synopsis above, comparing more than two lists at a time offers you
a wider, more complex palette of comparison methods. Individual items may appear in
just one source list, in all the source lists, or in some number of lists between one
and all. The meaning of 'union', 'intersection' and 'symmetric difference' is
conceptually unchanged when you move to multiple lists because these are properties of
all the lists considered together. In contrast, the meaning of 'unique',
'complement', 'subset' and 'equivalent' changes because these are properties of one
list compared with another or with all the other lists combined.
List::Compare takes this complexity into account by allowing you to pass arguments to
the public methods requesting results with respect to a specific list (for
"get_unique()" and "get_complement()") or a specific pair of lists (for
"is_LsubsetR()" and "is_LequivalentR()").
List::Compare further takes this complexity into account by offering the new methods
"get_shared()" and "get_nonintersection()" described in the Synopsis above.
• Multiple Accelerated Mode
Beginning with version 0.25, introduced in April 2004, List::Compare offers the
possibility of accelerated computation of a single comparison among three or more
lists at a time. Simply store the extra lists in arrays and pass references to those
arrays to the constructor preceded by the '-a' argument as was done with the simple
(two lists only) accelerated mode. List::Compare detects that more than two lists
have been passed to the constructor and silently switches into Multiple Accelerated
mode.
• Unsorted Option
When List::Compare is used to return lists representing various comparisons of two or
more lists (e.g., the lists' union or intersection), the lists returned are, by
default, sorted using Perl's default "sort" mode: ASCII-betical sorting. Sorting
produces results which are more easily human-readable but may entail a performance
cost.
Should you not need sorted results, you can avoid the potential performance cost by
calling List::Compare's constructor using the unsorted option. This is done by
calling '-u' or '--unsorted' as the first argument passed to the constructor, i.e., as
an argument called before any references to lists are passed to the constructor.
Note that if are calling List::Compare in the Accelerated or Multiple Accelerated mode
and wish to have the lists returned in unsorted order, you first pass the argument for
the unsorted option ('-u' or '--unsorted') and then pass the argument for the
Accelerated mode ('-a' or '--accelerated').
Miscellaneous Methods
It would not really be appropriate to call "get_shared()" and "get_nonintersection()" in
Regular or Accelerated mode since they are conceptually based on the notion of comparing
more than two lists at a time. However, there is always the possibility that a user may
be comparing only two lists (accelerated or not) and may accidentally call one of those
two methods. To prevent fatal run-time errors and to caution you to use a more
appropriate method, these two methods are defined for Regular and Accelerated modes so as
to return suitable results but also generate a carp message that advise you to re-code.
Similarly, the method "is_RsubsetL()" is appropriate for the Regular and Accelerated modes
but is not really appropriate for Multiple mode. As a defensive maneuver, it has been
defined for Multiple mode so as to return suitable results but also to generate a carp
message that advises you to re-code.
In List::Compare v0.11 and earlier, the author provided aliases for various methods based
on the supposition that the source lists would be referred to as 'A' and 'B'. Now that
you can compare more than two lists at a time, the author feels that it would be more
appropriate to refer to the elements of two-argument lists as the left-hand and right-hand
elements. Hence, we are discouraging the use of methods such as "get_Aonly()",
"get_Bonly()" and "get_AorBonly()" as aliases for "get_unique()", "get_complement()" and
"get_symmetric_difference()". However, to guarantee backwards compatibility for the vast
audience of Perl programmers using earlier versions of List::Compare (all 10e1 of you)
these and similar methods for subset relationships are still defined.
List::Compare::SeenHash Discontinued Beginning with Version 0.26
Prior to v0.26, introduced April 11, 2004, if a user wished to pass references to seen-
hashes to List::Compare's constructor rather than references to arrays, he or she had to
call a different, parallel module: List::Compare::SeenHash. The code for that looked like
this:
use List::Compare::SeenHash;
my %Llist = (
abel => 2,
baker => 1,
camera => 1,
delta => 1,
edward => 1,
fargo => 1,
golfer => 1,
);
my %Rlist = (
baker => 1,
camera => 1,
delta => 2,
edward => 1,
fargo => 1,
golfer => 1,
hilton => 1,
);
my $lcsh = List::Compare::SeenHash->new(\%Llist, \%Rlist);
List::Compare::SeenHash is deprecated beginning with version 0.26. All its functionality
(and more) has been implemented in List::Compare itself, since a user can now pass either
a series of array references or a series of seen-hash references to List::Compare's
constructor.
To simplify future maintenance of List::Compare, List::Compare::SeenHash.pm will no longer
be distributed with List::Compare, nor will the files in the test suite which tested
List::Compare::SeenHash upon installation be distributed.
Should you still need List::Compare::SeenHash, use version 0.25 from CPAN, or simply edit
your Perl programs which used List::Compare::SeenHash. Those scripts may be edited
quickly with, for example, this editing command in Unix text editor vi:
:1,$s/List::Compare::SeenHash/List::Compare/gc
A Non-Object-Oriented Interface: List::Compare::Functional
Version 0.21 of List::Compare introduced List::Compare::Functional, a functional (i.e.,
non-object-oriented) interface to list comparison functions. List::Compare::Functional
supports the same functions currently supported by List::Compare. It works similar to
List::Compare's Accelerated and Multiple Accelerated modes (described above), bit it does
not require use of the '-a' flag in the function call. List::Compare::Functional will
return unsorted comparisons of two lists by passing '-u' or '--unsorted' as the first
argument to the function. Please see the documentation for List::Compare::Functional to
learn how to import its functions into your main package.
ASSUMPTIONS AND QUALIFICATIONS
The program was created with Perl 5.6. The use of h2xs to prepare the module's template
installed "require 5.005_62;" at the top of the module. This has been commented out in
the actual module as the code appears to be compatible with earlier versions of Perl; how
earlier the author cannot say. In particular, the author would like the module to be
installable on older versions of MacPerl. As is, the author has successfully installed
the module on Linux, Windows 9x and Windows 2000. See
<http://testers.cpan.org/show/List-Compare.html> for a list of other systems on which this
version of List::Compare has been tested and installed.
HISTORY, REFERENCES AND DEVELOPMENT
The Code Itself
List::Compare is based on code presented by Tom Christiansen & Nathan Torkington in Perl
Cookbook <http://www.oreilly.com/catalog/cookbook/> (a.k.a. the 'Ram' book), O'Reilly &
Associates, 1998, Recipes 4.7 and 4.8. Similar code is presented in the Camel book:
Programming Perl, by Larry Wall, Tom Christiansen, Jon Orwant.
<http://www.oreilly.com/catalog/pperl3/>, 3rd ed, O'Reilly & Associates, 2000. The list
comparison code is so basic and Perlish that I suspect it may have been written by Larry
himself at the dawn of Perl time. The "get_bag()" method was inspired by Jarkko
Hietaniemi's Set::Bag module and Daniel Berger's Set::Array module, both available on
CPAN.
List::Compare's original objective was simply to put this code in a modular, object-
oriented framework. That framework, not surprisingly, is taken mostly from Damian
Conway's Object Oriented Perl <http://www.manning.com/Conway/index.html>, Manning
Publications, 2000.
With the addition of the Accelerated, Multiple and Multiple Accelerated modes,
List::Compare expands considerably in both size and capabilities. Nonetheless, Tom and
Nat's Cookbook code still lies at its core: the use of hashes as look-up tables to record
elements seen in lists. Please note: List::Compare is not concerned with any concept of
'equality' among lists which hinges upon the frequency with which, or the order in which,
elements appear in the lists to be compared. If this does not meet your needs, you should
look elsewhere or write your own module.
The Inspiration
I realized the usefulness of putting the list comparison code into a module while
preparing an introductory level Perl course given at the New School University's Computer
Instruction Center in April-May 2002. I was comparing lists left and right. When I found
myself writing very similar functions in different scripts, I knew a module was lurking
somewhere. I learned the truth of the mantra ''Repeated Code is a Mistake'' from a 2001
talk by Mark-Jason Dominus <http://perl.plover.com/> to the New York Perlmongers
<http://ny.pm.org/>. See <http://www.perl.com/pub/a/2000/11/repair3.html>.
The first public presentation of this module took place at Perl Seminar New York
<http://groups.yahoo.com/group/perlsemny> on May 21, 2002. Comments and suggestions were
provided there and since by Glenn Maciag, Gary Benson, Josh Rabinowitz, Terrence Brannon
and Dave Cross.
The placement in the installation tree of Test::ListCompareSpecial came as a result of a
question answered by Michael Graham in his talk ''Test::More to Test::Extreme'' given at
Yet Another Perl Conference::Canada in Ottawa, Ontario, on May 16, 2003.
In May-June 2003, Glenn Maciag made valuable suggestions which led to changes in method
names and documentation in v0.20.
Another presentation at Perl Seminar New York in October 2003 prompted me to begin
planning List::Compare::Functional.
In a November 2003 Perl Seminar New York presentation, Ben Holtzman discussed the
performance costs entailed in Perl's "sort" function. This led me to ask, ''Why should a
user of List::Compare pay this performance cost if he or she doesn't need a human-readable
list as a result (as would be the case if the list returned were used as the input into
some other function)?'' This led to the development of List::Compare's unsorted option.
An April 2004 offer by Kevin Carlson to write an article for The Perl Journal
(<http://tpj.com>) led me to re-think whether a separate module (the former
List::Compare::SeenHash) was truly needed when a user wanted to provide the constructor
with references to seen-hashes rather than references to arrays. Since I had already
adapted List::Compare::Functional to accept both kinds of arguments, I adapted
List::Compare in the same manner. This meant that List::Compare::SeenHash and its related
installation tests could be deprecated and deleted from the CPAN distribution.
A remark by David H. Adler at a New York Perlmongers meeting in April 2004 led me to
develop the 'single hashref' alternative constructor format, introduced in version 0.29
the following month.
Presentations at two different editions of Yet Another Perl Conference (YAPC) inspired the
development of List::Compare versions 0.30 and 0.31. I was selected to give a talk on
List::Compare at YAPC::NA::2004 in Buffalo. This spurred me to improve certain aspects of
the documentation. Version 0.31 owes its inspiration to one talk at the Buffalo YAPC and
one earlier talk at YAPC::EU::2003 in Paris. In Paris I heard Paul Johnson speak on his
CPAN module Devel::Cover and on coverage analysis more generally. That material was over
my head at that time, but in Buffalo I heard Andy Lester discuss Devel::Cover as part of
his discussion of testing and of the Phalanx project (<http://qa.perl.org/phalanx>). This
time I got it, and when I returned from Buffalo I applied Devel::Cover to List::Compare
and wrote additional tests to improve its subroutine and statement coverage. In addition,
I added two new methods, "get_unique_all" and "get_complement_all". In writing these two
methods, I followed a model of test-driven development much more so than in earlier
versions of List::Compare and my other CPAN modules. The result? List::Compare's test
suite grew by over 3300 tests to nearly 23,000 tests.
At the Second New York Perl Hackathon (May 02 2015), a project was created to request
performance improvements in certain List::Compare functions
(<https://github.com/nyperlmongers/nyperlhackathon2015/wiki/List-Compare-Performance-Improvements>).
Hackathon participant Michael Rawson submitted a pull request with changes to
List::Compare::Base::_Auxiliary. After these revisions were benchmarked, a patch
embodying the pull request was accepted, leading to CPAN version 0.53.
If You Like List::Compare, You'll Love ...
While preparing this module for distribution via CPAN, I had occasion to study a number of
other modules already available on CPAN. Each of these modules is more sophisticated than
List::Compare -- which is not surprising since all that List::Compare originally aspired
to do was to avoid typing Cookbook code repeatedly. Here is a brief description of the
features of these modules. (Warning: The following discussion is only valid as of June
2002. Some of these modules may have changed since then.)
• Algorithm::Diff - Compute 'intelligent' differences between two files/lists
(<http://search.cpan.org/dist/Algorithm-Diff/>)
Algorithm::Diff is a sophisticated module originally written by Mark-Jason Dominus,
later maintained by Ned Konz, now maintained by Tye McQueen. Think of the Unix "diff"
utility and you're on the right track. Algorithm::Diff exports methods such as
"diff", which ''computes the smallest set of additions and deletions necessary to turn
the first sequence into the second, and returns a description of these changes.''
Algorithm::Diff is mainly concerned with the sequence of elements within two lists.
It does not export functions for intersection, union, subset status, etc.
• Array::Compare - Perl extension for comparing arrays
(<http://search.cpan.org/dist/Array-Compare/>)
Array::Compare, by Dave Cross, asks whether two arrays are the same or different by
doing a "join" on each string with a separator character and comparing the resulting
strings. Like List::Compare, it is an object-oriented module. A sophisticated
feature of Array::Compare is that it allows you to specify how 'whitespace' in an
array (an element which is undefined, the empty string, or whitespace within an
element) should be evaluated for purpose of determining equality or difference. It
does not directly provide methods for intersection and union.
• Data::Compare - compare perl data structures
(<http://search.cpan.org/dist/Data-Compare/>)
This library compares Perl data structures recursively. Comes recommended by Slaven
Rezić!
• List::Util - A selection of general-utility list subroutines
(<http://search.cpan.org/dist/Scalar-List-Utils/>)
List::Util, by Graham Barr, exports a variety of simple, useful functions for
operating on one list at a time. The "min" function returns the lowest numerical
value in a list; the "max" function returns the highest value; and so forth.
List::Compare differs from List::Util in that it is object-oriented and that it works
on two strings at a time rather than just one -- but it aims to be as simple and
useful as List::Util. List::Util will be included in the standard Perl distribution
as of Perl 5.8.0.
Lists::Util (<http://search.cpan.org/dist/List-MoreUtils/>), by Tassilo von Parseval,
building on code by Terrence Brannon, provides methods which extend List::Util's
functionality.
• Quantum::Superpositions (<http://search.cpan.org/dist/Quantum-Superpositions/>),
originally by Damian Conway, now maintained by Steven Lembark is useful if, in
addition to comparing lists, you need to emulate quantum supercomputing as well. Not
for the eigen-challenged.
• Set::Scalar - basic set operations (<http://search.cpan.org/dist/Set-Scalar/>)
Set::Bag - bag (multiset) class (<http://search.cpan.org/dist/Set-Bag/>)
Both of these modules are by Jarkko Hietaniemi. Set::Scalar has methods to return the
intersection, union, difference and symmetric difference of two sets, as well as
methods to return items unique to a first set and complementary to it in a second set.
It has methods for reporting considerably more variants on subset status than does
List::Compare. However, benchmarking suggests that List::Compare, at least in Regular
mode, is considerably faster than Set::Scalar for those comparison methods which
List::Compare makes available.
Set::Bag enables one to deal more flexibly with the situation in which one has more
than one instance of an element in a list.
• Set::Array - Arrays as objects with lots of handy methods (including set comparisons)
and support for method chaining. (<http://search.cpan.org/dist/Set-Array/>)
Set::Array, by Daniel Berger, now maintained by Ron Savage, ''aims to provide built-in
methods for operations that people are always asking how to do,and which already exist
in languages like Ruby.'' Among the many methods in this module are some for
intersection, union, etc. To install Set::Array, you must first install the Want
module, also available on CPAN.
ADDITIONAL CONTRIBUTORS
• Syohei YOSHIDA
Pull request accepted May 22 2015.
• Paulo Custodio
Pull request accepted June 07 2015, correcting errors in "_subset_subengine()".
BUGS
There are no bug reports outstanding on List::Compare as of the most recent CPAN upload
date of this distribution.
SUPPORT
Please report any bugs by mail to "bug-List-Compare@rt.cpan.org" or through the web
interface at <http://rt.cpan.org>.
AUTHOR
James E. Keenan (jkeenan@cpan.org). When sending correspondence, please include
'List::Compare' or 'List-Compare' in your subject line.
Creation date: May 20, 2002. Last modification date: August 16 2020.
Development repository: <https://github.com/jkeenan/list-compare>
COPYRIGHT
Copyright (c) 2002-20 James E. Keenan. United States. All rights reserved. This is free
software and may be distributed under the same terms as Perl itself.
DISCLAIMER OF WARRANTY
BECAUSE THIS SOFTWARE IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY FOR THE SOFTWARE,
TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE
COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE SOFTWARE ''AS IS'' WITHOUT WARRANTY OF
ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS TO
THE QUALITY AND PERFORMANCE OF THE SOFTWARE IS WITH YOU. SHOULD THE SOFTWARE PROVE
DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR, OR CORRECTION.
IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING WILL ANY COPYRIGHT
HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR REDISTRIBUTE THE SOFTWARE AS PERMITTED BY
THE ABOVE LICENCE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL,
INCIDENTAL, OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE THE
SOFTWARE (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR
LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A FAILURE OF THE SOFTWARE TO OPERATE WITH ANY
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