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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 after after_incl before before_incl indexes
                                  firstval first_value lastval last_value each_array
                                  each_arrayref pairwise natatime mesh zip uniq minmax);

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 "undef" 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 "undef" 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 "undef" 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 "undef" 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 }

       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.

       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.

       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
           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 qw/: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.

VERSION
       This is version 0.22.

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/;

       Perl5.5.x and perl5.8.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).

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:

       o   uniq_by(&@)

           Use code-reference to extract a key based on which the uniqueness
           is determined. Suggested by Aaron Crane.

       o   delete_index

       o   random_item

       o   random_item_delete_index

       o   list_diff_hash

       o   list_diff_inboth

       o   list_diff_infirst

       o   list_diff_insecond

           These were all suggested by Dan Muey.

       o   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, <tassilo.von.parsevalATrwth-aachen.de>

COPYRIGHT AND LICENSE
       Copyright (C) 2004-2006 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 v5.10.0                      2006-07-02              List::MoreUtils(3pm)