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. Sets $_ for each item in LIST in turn:

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

       Returns false otherwise, or if LIST is empty.

   none 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 value defined"
               if none { defined($_) } @list;

       Returns false otherwise, or if LIST is empty.

   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 BLOCK 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
   Tassilo von Parseval <[email protected]>

COPYRIGHT AND LICENSE
   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.

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