Provided by: liblist-moreutils-perl_0.416-1build3_amd64 
NAME
List::MoreUtils - Provide the stuff missing in List::Util
SYNOPSIS
# import specific functions
use List::MoreUtils qw(any uniq);
if ( any { /foo/ } uniq @has_duplicates ) {
# do stuff
}
# import everything
use List::MoreUtils ':all';
# import by API
# has "original" any/all/none/notall behavior
use List::MoreUtils ':like_0.22';
# 0.22 + bsearch
use List::MoreUtils ':like_0.24';
# has "simplified" any/all/none/notall behavior + (n)sort_by
use List::MoreUtils ':like_0.33';
DESCRIPTION
List::MoreUtils provides some trivial but commonly needed functionality on lists which is
not going to go into List::Util.
All of the below functions are implementable in only a couple of lines of Perl code. Using
the functions from this module however should give slightly better performance as
everything is implemented in C. The pure-Perl implementation of these functions only
serves as a fallback in case the C portions of this module couldn't be compiled on this
machine.
EXPORTS
Default behavior
Nothing by default. To import all of this module's symbols use the ":all" tag. Otherwise
functions can be imported by name as usual:
use List::MoreUtils ':all';
use List::MoreUtils qw{ any firstidx };
Because historical changes to the API might make upgrading List::MoreUtils difficult for
some projects, the legacy API is available via special import tags.
Like version 0.22 (last release with original API)
This API was available from 2006 to 2009, returning undef for empty lists on
"all"/"any"/"none"/"notall":
use List::MoreUtils ':like_0.22';
This import tag will import all functions available as of version 0.22. However, it will
import "any_u" as "any", "all_u" as "all", "none_u" as "none", and "notall_u" as "notall".
Like version 0.24 (first incompatible change)
This API was available from 2010 to 2011. It changed the return value of "none" and added
the "bsearch" function.
use List::MoreUtils ':like_0.24';
This import tag will import all functions available as of version 0.24. However it will
import "any_u" as "any", "all_u" as "all", and "notall_u" as "notall". It will import
"none" as described in the documentation below (true for empty list).
Like version 0.33 (second incompatible change)
This API was available from 2011 to 2014. It is widely used in several CPAN modules and
thus it's closest to the current API. It changed the return values of "any", "all", and
"notall". It added the "sort_by" and "nsort_by" functions and the "distinct" alias for
"uniq". It omitted "bsearch".
use List::MoreUtils ':like_0.33';
This import tag will import all functions available as of version 0.33. Note: it will not
import "bsearch" for consistency with the 0.33 API.
FUNCTIONS
Junctions
Treatment of an empty list
There are two schools of thought for how to evaluate a junction on an empty list:
• Reduction to an identity (boolean)
• Result is undefined (three-valued)
In the first case, the result of the junction applied to the empty list is determined by a
mathematical reduction to an identity depending on whether the underlying comparison is
"or" or "and". Conceptually:
"any are true" "all are true"
-------------- --------------
2 elements: A || B || 0 A && B && 1
1 element: A || 0 A && 1
0 elements: 0 1
In the second case, three-value logic is desired, in which a junction applied to an empty
list returns "undef" rather than true or false
Junctions with a "_u" suffix implement three-valued logic. Those without are boolean.
all BLOCK LIST
all_u BLOCK LIST
Returns a true value if all items in LIST meet the criterion given through BLOCK. Sets $_
for each item in LIST in turn:
print "All values are non-negative"
if all { $_ >= 0 } ($x, $y, $z);
For an empty LIST, "all" returns true (i.e. no values failed the condition) and "all_u"
returns "undef".
Thus, "all_u(@list)" is equivalent to "@list ? all(@list) : undef".
Note: because Perl treats "undef" as false, you must check the return value of "all_u"
with "defined" or you will get the opposite result of what you expect.
any BLOCK LIST
any_u BLOCK LIST
Returns a true value if any item in LIST meets the criterion given through BLOCK. Sets $_
for each item in LIST in turn:
print "At least one non-negative value"
if any { $_ >= 0 } ($x, $y, $z);
For an empty LIST, "any" returns false and "any_u" returns "undef".
Thus, "any_u(@list)" is equivalent to "@list ? any(@list) : undef".
none BLOCK LIST
none_u BLOCK LIST
Logically the negation of "any". Returns a true value if no item in LIST meets the
criterion given through BLOCK. Sets $_ for each item in LIST in turn:
print "No non-negative values"
if none { $_ >= 0 } ($x, $y, $z);
For an empty LIST, "none" returns true (i.e. no values failed the condition) and "none_u"
returns "undef".
Thus, "none_u(@list)" is equivalent to "@list ? none(@list) : undef".
Note: because Perl treats "undef" as false, you must check the return value of "none_u"
with "defined" or you will get the opposite result of what you expect.
notall BLOCK LIST
notall_u BLOCK LIST
Logically the negation of "all". Returns a true value if not all items in LIST meet the
criterion given through BLOCK. Sets $_ for each item in LIST in turn:
print "Not all values are non-negative"
if notall { $_ >= 0 } ($x, $y, $z);
For an empty LIST, "notall" returns false and "notall_u" returns "undef".
Thus, "notall_u(@list)" is equivalent to "@list ? notall(@list) : undef".
one BLOCK LIST
one_u BLOCK LIST
Returns a true value if precisely one item in LIST meets the criterion given through
BLOCK. Sets $_ for each item in LIST in turn:
print "Precisely one value defined"
if one { defined($_) } @list;
Returns false otherwise.
For an empty LIST, "one" returns false and "one_u" returns "undef".
The expression "one BLOCK LIST" is almost equivalent to "1 == true BLOCK LIST", except for
short-cutting. Evaluation of BLOCK will immediately stop at the second true value.
Transformation
apply BLOCK LIST
Applies BLOCK to each item in LIST and returns a list of the values after BLOCK has been
applied. In scalar context, the last element is returned. This function is similar to
"map" but will not modify the elements of the input list:
my @list = (1 .. 4);
my @mult = apply { $_ *= 2 } @list;
print "\@list = @list\n";
print "\@mult = @mult\n";
__END__
@list = 1 2 3 4
@mult = 2 4 6 8
Think of it as syntactic sugar for
for (my @mult = @list) { $_ *= 2 }
insert_after BLOCK VALUE LIST
Inserts VALUE after the first item in LIST for which the criterion in BLOCK is true. Sets
$_ for each item in LIST in turn.
my @list = qw/This is a list/;
insert_after { $_ eq "a" } "longer" => @list;
print "@list";
__END__
This is a longer list
insert_after_string STRING VALUE LIST
Inserts VALUE after the first item in LIST which is equal to STRING.
my @list = qw/This is a list/;
insert_after_string "a", "longer" => @list;
print "@list";
__END__
This is a longer list
pairwise BLOCK ARRAY1 ARRAY2
Evaluates BLOCK for each pair of elements in ARRAY1 and ARRAY2 and returns a new list
consisting of BLOCK's return values. The two elements are set to $a and $b. Note that
those two are aliases to the original value so changing them will modify the input arrays.
@a = (1 .. 5);
@b = (11 .. 15);
@x = pairwise { $a + $b } @a, @b; # returns 12, 14, 16, 18, 20
# mesh with pairwise
@a = qw/a b c/;
@b = qw/1 2 3/;
@x = pairwise { ($a, $b) } @a, @b; # returns a, 1, b, 2, c, 3
mesh ARRAY1 ARRAY2 [ ARRAY3 ... ]
zip ARRAY1 ARRAY2 [ ARRAY3 ... ]
Returns a list consisting of the first elements of each array, then the second, then the
third, etc, until all arrays are exhausted.
Examples:
@x = qw/a b c d/;
@y = qw/1 2 3 4/;
@z = mesh @x, @y; # returns a, 1, b, 2, c, 3, d, 4
@a = ('x');
@b = ('1', '2');
@c = qw/zip zap zot/;
@d = mesh @a, @b, @c; # x, 1, zip, undef, 2, zap, undef, undef, zot
"zip" is an alias for "mesh".
uniq LIST
distinct LIST
Returns a new list by stripping duplicate values in LIST by comparing the values as hash
keys, except that undef is considered separate from ''. The order of elements in the
returned list is the same as in LIST. In scalar context, returns the number of unique
elements in LIST.
my @x = uniq 1, 1, 2, 2, 3, 5, 3, 4; # returns 1 2 3 5 4
my $x = uniq 1, 1, 2, 2, 3, 5, 3, 4; # returns 5
# returns "Mike", "Michael", "Richard", "Rick"
my @n = distinct "Mike", "Michael", "Richard", "Rick", "Michael", "Rick"
# returns '', 'S1', A5' and complains about "Use of uninitialized value"
my @s = distinct '', undef, 'S1', 'A5'
# returns undef, 'S1', A5' and complains about "Use of uninitialized value"
my @w = uniq undef, '', 'S1', 'A5'
"distinct" is an alias for "uniq".
RT#49800 can be used to give feedback about this behavior.
singleton
Returns a new list by stripping values in LIST occurring more than once by comparing the
values as hash keys, except that undef is considered separate from ''. The order of
elements in the returned list is the same as in LIST. In scalar context, returns the
number of elements occurring only once in LIST.
my @x = singleton 1,1,2,2,3,4,5 # returns 3 4 5
Partitioning
after BLOCK LIST
Returns a list of the values of LIST after (and not including) the point where BLOCK
returns a true value. Sets $_ for each element in LIST in turn.
@x = after { $_ % 5 == 0 } (1..9); # returns 6, 7, 8, 9
after_incl BLOCK LIST
Same as "after" but also includes the element for which BLOCK is true.
before BLOCK LIST
Returns a list of values of LIST up to (and not including) the point where BLOCK returns a
true value. Sets $_ for each element in LIST in turn.
before_incl BLOCK LIST
Same as "before" but also includes the element for which BLOCK is true.
part BLOCK LIST
Partitions LIST based on the return value of BLOCK which denotes into which partition the
current value is put.
Returns a list of the partitions thusly created. Each partition created is a reference to
an array.
my $i = 0;
my @part = part { $i++ % 2 } 1 .. 8; # returns [1, 3, 5, 7], [2, 4, 6, 8]
You can have a sparse list of partitions as well where non-set partitions will be undef:
my @part = part { 2 } 1 .. 10; # returns undef, undef, [ 1 .. 10 ]
Be careful with negative values, though:
my @part = part { -1 } 1 .. 10;
__END__
Modification of non-creatable array value attempted, subscript -1 ...
Negative values are only ok when they refer to a partition previously created:
my @idx = ( 0, 1, -1 );
my $i = 0;
my @part = part { $idx[$++ % 3] } 1 .. 8; # [1, 4, 7], [2, 3, 5, 6, 8]
Iteration
each_array ARRAY1 ARRAY2 ...
Creates an array iterator to return the elements of the list of arrays ARRAY1, ARRAY2
throughout ARRAYn in turn. That is, the first time it is called, it returns the first
element of each array. The next time, it returns the second elements. And so on, until
all elements are exhausted.
This is useful for looping over more than one array at once:
my $ea = each_array(@a, @b, @c);
while ( my ($a, $b, $c) = $ea->() ) { .... }
The iterator returns the empty list when it reached the end of all arrays.
If the iterator is passed an argument of '"index"', then it returns the index of the last
fetched set of values, as a scalar.
each_arrayref LIST
Like each_array, but the arguments are references to arrays, not the plain arrays.
natatime EXPR, LIST
Creates an array iterator, for looping over an array in chunks of $n items at a time. (n
at a time, get it?). An example is probably a better explanation than I could give in
words.
Example:
my @x = ('a' .. 'g');
my $it = natatime 3, @x;
while (my @vals = $it->())
{
print "@vals\n";
}
This prints
a b c
d e f
g
Searching
bsearch BLOCK LIST
Performs a binary search on LIST which must be a sorted list of values. BLOCK must return
a negative value if the current element (stored in $_) is smaller, a positive value if it
is bigger and zero if it matches.
Returns a boolean value in scalar context. In list context, it returns the element if it
was found, otherwise the empty list.
bsearchidx BLOCK LIST
bsearch_index BLOCK LIST
Performs a binary search on LIST which must be a sorted list of values. BLOCK must return
a negative value if the current element (stored in $_) is smaller, a positive value if it
is bigger and zero if it matches.
Returns the index of found element, otherwise "-1".
"bsearch_index" is an alias for "bsearchidx".
firstval BLOCK LIST
first_value BLOCK LIST
Returns the first element in LIST for which BLOCK evaluates to true. Each element of LIST
is set to $_ in turn. Returns "undef" if no such element has been found.
"first_value" is an alias for "firstval".
onlyval BLOCK LIST
only_value BLOCK LIST
Returns the only element in LIST for which BLOCK evaluates to true. Sets $_ for each item
in LIST in turn. Returns "undef" if no such element has been found.
"only_value" is an alias for "onlyval".
lastval BLOCK LIST
last_value BLOCK LIST
Returns the last value in LIST for which BLOCK evaluates to true. Each element of LIST is
set to $_ in turn. Returns "undef" if no such element has been found.
"last_value" is an alias for "lastval".
firstres BLOCK LIST
first_result BLOCK LIST
Returns the result of BLOCK for the first element in LIST for which BLOCK evaluates to
true. Each element of LIST is set to $_ in turn. Returns "undef" if no such element has
been found.
"first_result" is an alias for "firstres".
onlyres BLOCK LIST
only_result BLOCK LIST
Returns the result of BLOCK for the first element in LIST for which BLOCK evaluates to
true. Sets $_ for each item in LIST in turn. Returns "undef" if no such element has been
found.
"only_result" is an alias for "onlyres".
lastres BLOCK LIST
last_result BLOCK LIST
Returns the result of BLOCK for the last element in LIST for which BLOCK evaluates to
true. Each element of LIST is set to $_ in turn. Returns "undef" if no such element has
been found.
"last_result" is an alias for "lastres".
indexes BLOCK LIST
Evaluates BLOCK for each element in LIST (assigned to $_) and returns a list of the
indices of those elements for which BLOCK returned a true value. This is just like "grep"
only that it returns indices instead of values:
@x = indexes { $_ % 2 == 0 } (1..10); # returns 1, 3, 5, 7, 9
firstidx BLOCK LIST
first_index BLOCK LIST
Returns the index of the first element in LIST for which the criterion in BLOCK is true.
Sets $_ for each item in LIST in turn:
my @list = (1, 4, 3, 2, 4, 6);
printf "item with index %i in list is 4", firstidx { $_ == 4 } @list;
__END__
item with index 1 in list is 4
Returns "-1" if no such item could be found.
"first_index" is an alias for "firstidx".
onlyidx BLOCK LIST
only_index BLOCK LIST
Returns the index of the only element in LIST for which the criterion in BLOCK is true.
Sets $_ for each item in LIST in turn:
my @list = (1, 3, 4, 3, 2, 4);
printf "uniqe index of item 2 in list is %i", onlyidx { $_ == 2 } @list;
__END__
unique index of item 2 in list is 4
Returns "-1" if either no such item or more than one of these has been found.
"only_index" is an alias for "onlyidx".
lastidx BLOCK LIST
last_index BLOCK LIST
Returns the index of the last element in LIST for which the criterion in BLOCK is true.
Sets $_ for each item in LIST in turn:
my @list = (1, 4, 3, 2, 4, 6);
printf "item with index %i in list is 4", lastidx { $_ == 4 } @list;
__END__
item with index 4 in list is 4
Returns "-1" if no such item could be found.
"last_index" is an alias for "lastidx".
Sorting
sort_by BLOCK LIST
Returns the list of values sorted according to the string values returned by the KEYFUNC
block or function. A typical use of this may be to sort objects according to the string
value of some accessor, such as
sort_by { $_->name } @people
The key function is called in scalar context, being passed each value in turn as both $_
and the only argument in the parameters, @_. The values are then sorted according to
string comparisons on the values returned. This is equivalent to
sort { $a->name cmp $b->name } @people
except that it guarantees the name accessor will be executed only once per value. One
interesting use-case is to sort strings which may have numbers embedded in them
"naturally", rather than lexically.
sort_by { s/(\d+)/sprintf "%09d", $1/eg; $_ } @strings
This sorts strings by generating sort keys which zero-pad the embedded numbers to some
level (9 digits in this case), helping to ensure the lexical sort puts them in the correct
order.
nsort_by BLOCK LIST
Similar to sort_by but compares its key values numerically.
Counting and calculation
true BLOCK LIST
Counts the number of elements in LIST for which the criterion in BLOCK is true. Sets $_
for each item in LIST in turn:
printf "%i item(s) are defined", true { defined($_) } @list;
false BLOCK LIST
Counts the number of elements in LIST for which the criterion in BLOCK is false. Sets $_
for each item in LIST in turn:
printf "%i item(s) are not defined", false { defined($_) } @list;
minmax LIST
Calculates the minimum and maximum of LIST and returns a two element list with the first
element being the minimum and the second the maximum. Returns the empty list if LIST was
empty.
The "minmax" algorithm differs from a naive iteration over the list where each element is
compared to two values being the so far calculated min and max value in that it only
requires 3n/2 - 2 comparisons. Thus it is the most efficient possible algorithm.
However, the Perl implementation of it has some overhead simply due to the fact that there
are more lines of Perl code involved. Therefore, LIST needs to be fairly big in order for
"minmax" to win over a naive implementation. This limitation does not apply to the XS
version.
ENVIRONMENT
When "LIST_MOREUTILS_PP" is set, the module will always use the pure-Perl implementation
and not the XS one. This environment variable is really just there for the test-suite to
force testing the Perl implementation, and possibly for reporting of bugs. I don't see any
reason to use it in a production environment.
MAINTENANCE
The maintenance goal is to preserve the documented semantics of the API; bug fixes that
bring actual behavior in line with semantics are allowed. New API functions may be added
over time. If a backwards incompatible change is unavoidable, we will attempt to provide
support for the legacy API using the same export tag mechanism currently in place.
This module attempts to use few non-core dependencies. Non-core configuration and testing
modules will be bundled when reasonable; run-time dependencies will be added only if they
deliver substantial benefit.
CONTRIBUTING
While contributions are appreciated, a contribution should not cause more effort for the
maintainer than the contribution itself saves (see Open Source Contribution Etiquette
<http://tirania.org/blog/archive/2010/Dec-31.html>).
To get more familiar where help could be needed - see List::MoreUtils::Contributing.
BUGS
There is a problem with a bug in 5.6.x perls. It is a syntax error to write things like:
my @x = apply { s/foo/bar/ } qw{ foo bar baz };
It has to be written as either
my @x = apply { s/foo/bar/ } 'foo', 'bar', 'baz';
or
my @x = apply { s/foo/bar/ } my @dummy = qw/foo bar baz/;
Perl 5.5.x and Perl 5.8.x don't suffer from this limitation.
If you have a functionality that you could imagine being in this module, please drop me a
line. This module's policy will be less strict than List::Util's when it comes to
additions as it isn't a core module.
When you report bugs, it would be nice if you could additionally give me the output of
your program with the environment variable "LIST_MOREUTILS_PP" set to a true value. That
way I know where to look for the problem (in XS, pure-Perl or possibly both).
SUPPORT
Bugs should always be submitted via the CPAN bug tracker.
You can find documentation for this module with the perldoc command.
perldoc List::MoreUtils
You can also look for information at:
• RT: CPAN's request tracker
<https://rt.cpan.org/Dist/Display.html?Name=List-MoreUtils>
• AnnoCPAN: Annotated CPAN documentation
<http://annocpan.org/dist/List-MoreUtils>
• CPAN Ratings
<http://cpanratings.perl.org/dist/List-MoreUtils>
• MetaCPAN
<https://metacpan.org/release/List-MoreUtils>
• CPAN Search
<http://search.cpan.org/dist/List-MoreUtils/>
• Git Repository
<https://github.com/perl5-utils/List-MoreUtils>
Where can I go for help?
If you have a bug report, a patch or a suggestion, please open a new report ticket at CPAN
(but please check previous reports first in case your issue has already been addressed) or
open an issue on GitHub.
Report tickets should contain a detailed description of the bug or enhancement request and
at least an easily verifiable way of reproducing the issue or fix. Patches are always
welcome, too - and it's cheap to send pull-requests on GitHub. Please keep in mind that
code changes are more likely accepted when they're bundled with an approving test.
If you think you've found a bug then please read "How to Report Bugs Effectively" by Simon
Tatham: <http://www.chiark.greenend.org.uk/~sgtatham/bugs.html>.
Where can I go for help with a concrete version?
Bugs and feature requests are accepted against the latest version only. To get patches for
earlier versions, you need to get an agreement with a developer of your choice - who may
or not report the issue and a suggested fix upstream (depends on the license you have
chosen).
Business support and maintenance
Generally, in volunteered projects, there is no right for support. While every maintainer
is happy to improve the provided software, spare time is limited.
For those who have a use case which requires guaranteed support, one of the maintainers
should be hired or contracted. For business support you can contact Jens via his CPAN
email address rehsackATcpan.org. Please keep in mind that business support is neither
available for free nor are you eligible to receive any support based on the license
distributed with this package.
THANKS
Tassilo von Parseval
Credits go to a number of people: Steve Purkis for giving me namespace advice and James
Keenan and Terrence Branno for their effort of keeping the CPAN tidier by making
List::Utils obsolete.
Brian McCauley suggested the inclusion of apply() and provided the pure-Perl
implementation for it.
Eric J. Roode asked me to add all functions from his module "List::MoreUtil" into this
one. With minor modifications, the pure-Perl implementations of those are by him.
The bunch of people who almost immediately pointed out the many problems with the glitchy
0.07 release (Slaven Rezic, Ron Savage, CPAN testers).
A particularly nasty memory leak was spotted by Thomas A. Lowery.
Lars Thegler made me aware of problems with older Perl versions.
Anno Siegel de-orphaned each_arrayref().
David Filmer made me aware of a problem in each_arrayref that could ultimately lead to a
segfault.
Ricardo Signes suggested the inclusion of part() and provided the Perl-implementation.
Robin Huston kindly fixed a bug in perl's MULTICALL API to make the XS-implementation of
part() work.
Jens Rehsack
Credits goes to all people contributing feedback during the v0.400 development releases.
Special thanks goes to David Golden who spent a lot of effort to develop a design to
support current state of CPAN as well as ancient software somewhere in the dark. He also
contributed a lot of patches to refactor the API frontend to welcome any user of
List::MoreUtils - from ancient past to recently last used.
Toby Inkster provided a lot of useful feedback for sane importer code and was a nice
sounding board for API discussions.
Peter Rabbitson provided a sane git repository setup containing entire package history.
TODO
A pile of requests from other people is still pending further processing in my mailbox.
This includes:
• List::Util export pass-through
Allow List::MoreUtils to pass-through the regular List::Util functions to end users
only need to "use" the one module.
• uniq_by(&@)
Use code-reference to extract a key based on which the uniqueness is determined.
Suggested by Aaron Crane.
• delete_index
• random_item
• random_item_delete_index
• list_diff_hash
• list_diff_inboth
• list_diff_infirst
• list_diff_insecond
These were all suggested by Dan Muey.
• listify
Always return a flat list when either a simple scalar value was passed or an array-
reference. Suggested by Mark Summersault.
SEE ALSO
List::Util, List::AllUtils, List::UtilsBy
AUTHOR
Jens Rehsack <rehsack AT cpan.org>
Adam Kennedy <adamk@cpan.org>
Tassilo von Parseval <tassilo.von.parseval@rwth-aachen.de>
COPYRIGHT AND LICENSE
Some parts copyright 2011 Aaron Crane.
Copyright 2004 - 2010 by Tassilo von Parseval
Copyright 2013 - 2016 by Jens Rehsack
This library is free software; you can redistribute it and/or modify it under the same
terms as Perl itself, either Perl version 5.8.4 or, at your option, any later version of
Perl 5 you may have available.