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List::MoreUtils(3pm)  User Contributed Perl Documentation List::MoreUtils(3pm)

NAME
       List::MoreUtils - Provide the stuff missing in List::Util

SYNOPSIS
	   use List::MoreUtils qw{
	       any all none notall true false
	       firstidx first_index lastidx last_index
	       insert_after insert_after_string
	       apply indexes
	       after after_incl before before_incl
	       firstval first_value lastval last_value
	       each_array each_arrayref
	       pairwise natatime
	       mesh zip uniq distinct minmax part
	   };

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.

       any 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 value undefined"
		   if any { ! defined($_) } @list;

	   Returns false otherwise, or if LIST is empty.

       all BLOCK LIST
	   Returns a true value if all items in LIST meet the criterion given
	   through BLOCK, or if LIST is empty. Sets $_ for each item in LIST
	   in turn:

	       print "All items defined"
		   if all { defined($_) } @list;

	   Returns false otherwise.

       none BLOCK LIST
	   Logically the negation of "any". Returns a true value if no item in
	   LIST meets the criterion given through BLOCK, or if LIST is empty.
	   Sets $_ for each item in LIST in turn:

	       print "No value defined"
		   if none { defined($_) } @list;

	   Returns false otherwise.

       notall 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 defined"
		   if notall { defined($_) } @list;

	   Returns false otherwise, or if LIST is empty.

       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;

       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".

       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".

       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

       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 }

       before BLOCK LIST
	   Returns a list of values of LIST upto (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.

       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 inclues the element for which BLOCK is
	   true.

       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

       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_val" is an alias for "firstval".

       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_val" is an alias for "lastval".

       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

       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 retuns
	   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

       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. 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

       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.

       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]

EXPORTS
       Nothing by default. To import all of this module's symbols, do the
       conventional

	   use List::MoreUtils ':all';

       It may make more sense though to only import the stuff your program
       actually needs:

	   use List::MoreUtils qw{ any firstidx };

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.

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.

       <http://rt.cpan.org/NoAuth/ReportBug.html?Queue=List-MoreUtils>

THANKS
       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.

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

AUTHOR
       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

       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.

perl v5.18.1			  2011-08-04		  List::MoreUtils(3pm)
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