{ name => "Image::Info", url => "http://search.cpan.org/~srezic/", debian => 'libimage-info-perl' },
{ name => "JSON", url => "http://search.cpan.org/~makamaka", debian => 'libjson-perl' },
{ name => "List::MoreUtils", version => '0.21', url => "http://search.cpan.org/~vparseval/", debian => 'liblist-moreutils-perl' },
+ { name => "List::UtilsBy", url => "http://search.cpan.org/~pevans/", debian => 'liblist-utilsby-perl' },
{ name => "Params::Validate", url => "http://search.cpan.org/~drolsky/", debian => 'libparams-validate-perl' },
{ name => "PDF::API2", version => '2.000', url => "http://search.cpan.org/~areibens/", debian => 'libpdf-api2-perl' },
{ name => "Rose::Object", url => "http://search.cpan.org/~jsiracusa/", debian => 'librose-object-perl' },
--- /dev/null
+This software is copyright (c) 2012 by Paul Evans <leonerd@leonerd.org.uk>.
+
+This is free software; you can redistribute it and/or modify it under
+the same terms as the Perl 5 programming language system itself.
+
+Terms of the Perl programming language system itself
+
+a) the GNU General Public License as published by the Free
+ Software Foundation; either version 1, or (at your option) any
+ later version, or
+b) the "Artistic License"
+
+--- The GNU General Public License, Version 1, February 1989 ---
+
+This software is Copyright (c) 2012 by Paul Evans <leonerd@leonerd.org.uk>.
+
+This is free software, licensed under:
+
+ The GNU General Public License, Version 1, February 1989
+
+ GNU GENERAL PUBLIC LICENSE
+ Version 1, February 1989
+
+ Copyright (C) 1989 Free Software Foundation, Inc.
+ 51 Franklin St, Suite 500, Boston, MA 02110-1335 USA
+
+ Everyone is permitted to copy and distribute verbatim copies
+ of this license document, but changing it is not allowed.
+
+ Preamble
+
+ The license agreements of most software companies try to keep users
+at the mercy of those companies. By contrast, our General Public
+License is intended to guarantee your freedom to share and change free
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+
+ When we speak of free software, we are referring to freedom, not
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+ The precise terms and conditions for copying, distribution and
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+
+ GNU GENERAL PUBLIC LICENSE
+ TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
+
+ 0. This License Agreement applies to any program or other work which
+contains a notice placed by the copyright holder saying it may be
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+ NO WARRANTY
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+
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+
+ END OF TERMS AND CONDITIONS
+
+ Appendix: How to Apply These Terms to Your New Programs
+
+ If you develop a new program, and you want it to be of the greatest
+possible use to humanity, the best way to achieve this is to make it
+free software which everyone can redistribute and change under these
+terms.
+
+ To do so, attach the following notices to the program. It is safest to
+attach them to the start of each source file to most effectively convey
+the exclusion of warranty; and each file should have at least the
+"copyright" line and a pointer to where the full notice is found.
+
+ <one line to give the program's name and a brief idea of what it does.>
+ Copyright (C) 19yy <name of author>
+
+ This program is free software; you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published by
+ the Free Software Foundation; either version 1, or (at your option)
+ any later version.
+
+ This program is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with this program; if not, write to the Free Software
+ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301 USA
+
+
+Also add information on how to contact you by electronic and paper mail.
+
+If the program is interactive, make it output a short notice like this
+when it starts in an interactive mode:
+
+ Gnomovision version 69, Copyright (C) 19xx name of author
+ Gnomovision comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
+ This is free software, and you are welcome to redistribute it
+ under certain conditions; type `show c' for details.
+
+The hypothetical commands `show w' and `show c' should show the
+appropriate parts of the General Public License. Of course, the
+commands you use may be called something other than `show w' and `show
+c'; they could even be mouse-clicks or menu items--whatever suits your
+program.
+
+You should also get your employer (if you work as a programmer) or your
+school, if any, to sign a "copyright disclaimer" for the program, if
+necessary. Here a sample; alter the names:
+
+ Yoyodyne, Inc., hereby disclaims all copyright interest in the
+ program `Gnomovision' (a program to direct compilers to make passes
+ at assemblers) written by James Hacker.
+
+ <signature of Ty Coon>, 1 April 1989
+ Ty Coon, President of Vice
+
+That's all there is to it!
+
+
+--- The Artistic License 1.0 ---
+
+This software is Copyright (c) 2012 by Paul Evans <leonerd@leonerd.org.uk>.
+
+This is free software, licensed under:
+
+ The Artistic License 1.0
+
+The Artistic License
+
+Preamble
+
+The intent of this document is to state the conditions under which a Package
+may be copied, such that the Copyright Holder maintains some semblance of
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+
+1. You may make and give away verbatim copies of the source form of the
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+
+ d) make other distribution arrangements with the Copyright Holder.
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+5. You may charge a reasonable copying fee for any distribution of this
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+from the programs of this Package do not automatically fall under the copyright
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+
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+be considered part of this Package.
+
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+products derived from this software without specific prior written permission.
+
+9. THIS PACKAGE IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS OR IMPLIED
+WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
+MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
+
+The End
--- /dev/null
+NAME
+ `List::UtilsBy' - higher-order list utility functions
+
+SYNOPSIS
+ use List::UtilsBy qw( nsort_by min_by );
+
+ use File::stat qw( stat );
+ my @files_by_age = nsort_by { stat($_)->mtime } @files;
+
+ my $shortest_name = min_by { length } @names;
+
+DESCRIPTION
+ This module provides a number of list utility functions, all of which
+ take an initial code block to control their behaviour. They are
+ variations on similar core perl or `List::Util' functions of similar
+ names, but which use the block to control their behaviour. For example,
+ the core Perl function `sort' takes a list of values and returns them,
+ sorted into order by their string value. The `sort_by' function sorts
+ them according to the string value returned by the extra function, when
+ given each value.
+
+ my @names_sorted = sort @names;
+
+ my @people_sorted = sort_by { $_->name } @people;
+
+FUNCTIONS
+ @vals = sort_by { KEYFUNC } @vals
+ 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.
+
+ @vals = nsort_by { KEYFUNC } @vals
+ Similar to `sort_by' but compares its key values numerically.
+
+ @vals = rev_sort_by { KEYFUNC } @vals
+ @vals = rev_nsort_by { KEYFUNC } @vals
+ Similar to `sort_by' and `nsort_by' but returns the list in the reverse
+ order. Equivalent to
+
+ @vals = reverse sort_by { KEYFUNC } @vals
+
+ except that these functions are slightly more efficient because they
+ avoid the final `reverse' operation.
+
+ $optimal = max_by { KEYFUNC } @vals
+ @optimal = max_by { KEYFUNC } @vals
+ Returns the (first) value from `@vals' that gives the numerically
+ largest result from the key function.
+
+ my $tallest = max_by { $_->height } @people
+
+ use File::stat qw( stat );
+ my $newest = max_by { stat($_)->mtime } @files;
+
+ In scalar context, the first maximal value is returned. In list context,
+ a list of all the maximal values is returned. This may be used to obtain
+ positions other than the first, if order is significant.
+
+ If called on an empty list, an empty list is returned.
+
+ For symmetry with the `nsort_by' function, this is also provided under
+ the name `nmax_by' since it behaves numerically.
+
+ $optimal = min_by { KEYFUNC } @vals
+ @optimal = min_by { KEYFUNC } @vals
+ Similar to `max_by' but returns values which give the numerically
+ smallest result from the key function. Also provided as `nmin_by'
+
+ @vals = uniq_by { KEYFUNC } @vals
+ Returns a list of the subset of values for which the key function block
+ returns unique values. The first value yielding a particular key is
+ chosen, subsequent values are rejected.
+
+ my @some_fruit = uniq_by { $_->colour } @fruit;
+
+ To select instead the last value per key, reverse the input list. If the
+ order of the results is significant, don't forget to reverse the result
+ as well:
+
+ my @some_fruit = reverse uniq_by { $_->colour } reverse @fruit;
+
+ %parts = partition_by { KEYFUNC } @vals
+ Returns a key/value list of ARRAY refs containing all the original
+ values distributed according to the result of the key function block.
+ Each value will be an ARRAY ref containing all the values which returned
+ the string from the key function, in their original order.
+
+ my %balls_by_colour = partition_by { $_->colour } @balls;
+
+ Because the values returned by the key function are used as hash keys,
+ they ought to either be strings, or at least well-behaved as strings
+ (such as numbers, or object references which overload stringification in
+ a suitable manner).
+
+ %counts = count_by { KEYFUNC } @vals
+ Returns a key/value list of integers, giving the number of times the key
+ function block returned the key, for each value in the list.
+
+ my %count_of_balls = count_by { $_->colour } @balls;
+
+ Because the values returned by the key function are used as hash keys,
+ they ought to either be strings, or at least well-behaved as strings
+ (such as numbers, or object references which overload stringification in
+ a suitable manner).
+
+ @vals = zip_by { ITEMFUNC } \@arr0, \@arr1, \@arr2,...
+ Returns a list of each of the values returned by the function block,
+ when invoked with values from across each each of the given ARRAY
+ references. Each value in the returned list will be the result of the
+ function having been invoked with arguments at that position, from
+ across each of the arrays given.
+
+ my @transposition = zip_by { [ @_ ] } @matrix;
+
+ my @names = zip_by { "$_[1], $_[0]" } \@firstnames, \@surnames;
+
+ print zip_by { "$_[0] => $_[1]\n" } [ keys %hash ], [ values %hash ];
+
+ If some of the arrays are shorter than others, the function will behave
+ as if they had `undef' in the trailing positions. The following two
+ lines are equivalent:
+
+ zip_by { f(@_) } [ 1, 2, 3 ], [ "a", "b" ]
+ f( 1, "a" ), f( 2, "b" ), f( 3, undef )
+
+ The item function is called by `map', so if it returns a list, the
+ entire list is included in the result. This can be useful for example,
+ for generating a hash from two separate lists of keys and values
+
+ my %nums = zip_by { @_ } [qw( one two three )], [ 1, 2, 3 ];
+ # %nums = ( one => 1, two => 2, three => 3 )
+
+ (A function having this behaviour is sometimes called `zipWith', e.g. in
+ Haskell, but that name would not fit the naming scheme used by this
+ module).
+
+ $arr0, $arr1, $arr2, ... = unzip_by { ITEMFUNC } @vals
+ Returns a list of ARRAY references containing the values returned by the
+ function block, when invoked for each of the values given in the input
+ list. Each of the returned ARRAY references will contain the values
+ returned at that corresponding position by the function block. That is,
+ the first returned ARRAY reference will contain all the values returned
+ in the first position by the function block, the second will contain all
+ the values from the second position, and so on.
+
+ my ( $firstnames, $lastnames ) = unzip_by { m/^(.*?) (.*)$/ } @names;
+
+ If the function returns lists of differing lengths, the result will be
+ padded with `undef' in the missing elements.
+
+ This function is an inverse of `zip_by', if given a corresponding
+ inverse function.
+
+ @vals = extract_by { SELECTFUNC } @arr
+ Removes elements from the referenced array on which the selection
+ function returns true, and returns a list containing those elements.
+ This function is similar to `grep', except that it modifies the
+ referenced array to remove the selected values from it, leaving only the
+ unselected ones.
+
+ my @red_balls = extract_by { $_->color eq "red" } @balls;
+
+ # Now there are no red balls in the @balls array
+
+ This function modifies a real array, unlike most of the other functions
+ in this module. Because of this, it requires a real array, not just a
+ list.
+
+ This function is implemented by invoking `splice()' on the array, not by
+ constructing a new list and assigning it. One result of this is that
+ weak references will not be disturbed.
+
+ extract_by { !defined $_ } @refs;
+
+ will leave weak references weakened in the `@refs' array, whereas
+
+ @refs = grep { defined $_ } @refs;
+
+ will strengthen them all again.
+
+ @vals = weighted_shuffle_by { WEIGHTFUNC } @vals
+ Returns the list of values shuffled into a random order. The
+ randomisation is not uniform, but weighted by the value returned by the
+ `WEIGHTFUNC'. The probabilty of each item being returned first will be
+ distributed with the distribution of the weights, and so on recursively
+ for the remaining items.
+
+ @vals = bundle_by { BLOCKFUNC } $number, @vals
+ Similar to a regular `map' functional, returns a list of the values
+ returned by `BLOCKFUNC'. Values from the input list are given to the
+ block function in bundles of `$number'.
+
+ If given a list of values whose length does not evenly divide by
+ `$number', the final call will be passed fewer elements than the others.
+
+TODO
+ * XS implementations
+ These functions are currently all written in pure perl. Some at
+ least, may benefit from having XS implementations to speed up their
+ logic.
+
+ * Merge into List::Util or List::MoreUtils
+ This module shouldn't really exist. The functions should instead be
+ part of one of the existing modules that already contain many list
+ utility functions. Having Yet Another List Utilty Module just
+ worsens the problem.
+
+ I have attempted to contact the authors of both of the above
+ modules, to no avail; therefore I decided it best to write and
+ release this code here anyway so that it is at least on CPAN. Once
+ there, we can then see how best to merge it into an existing module.
+
+AUTHOR
+ Paul Evans <leonerd@leonerd.org.uk>
--- /dev/null
+# You may distribute under the terms of either the GNU General Public License
+# or the Artistic License (the same terms as Perl itself)
+#
+# (C) Paul Evans, 2009-2012 -- leonerd@leonerd.org.uk
+
+package List::UtilsBy;
+
+use strict;
+use warnings;
+
+our $VERSION = '0.09';
+
+use Exporter 'import';
+
+our @EXPORT_OK = qw(
+ sort_by
+ nsort_by
+ rev_sort_by
+ rev_nsort_by
+
+ max_by nmax_by
+ min_by nmin_by
+
+ uniq_by
+
+ partition_by
+ count_by
+
+ zip_by
+ unzip_by
+
+ extract_by
+
+ weighted_shuffle_by
+
+ bundle_by
+);
+
+=head1 NAME
+
+C<List::UtilsBy> - higher-order list utility functions
+
+=head1 SYNOPSIS
+
+ use List::UtilsBy qw( nsort_by min_by );
+
+ use File::stat qw( stat );
+ my @files_by_age = nsort_by { stat($_)->mtime } @files;
+
+ my $shortest_name = min_by { length } @names;
+
+=head1 DESCRIPTION
+
+This module provides a number of list utility functions, all of which take an
+initial code block to control their behaviour. They are variations on similar
+core perl or C<List::Util> functions of similar names, but which use the block
+to control their behaviour. For example, the core Perl function C<sort> takes
+a list of values and returns them, sorted into order by their string value.
+The C<sort_by> function sorts them according to the string value returned by
+the extra function, when given each value.
+
+ my @names_sorted = sort @names;
+
+ my @people_sorted = sort_by { $_->name } @people;
+
+=cut
+
+=head1 FUNCTIONS
+
+=cut
+
+=head2 @vals = sort_by { KEYFUNC } @vals
+
+Returns the list of values sorted according to the string values returned by
+the C<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 { $_->name } @people
+
+The key function is called in scalar context, being passed each value in turn
+as both C<$_> and the only argument in the parameters, C<@_>. 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 C<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.
+
+=cut
+
+sub sort_by(&@)
+{
+ my $keygen = shift;
+
+ my @keys = map { local $_ = $_; scalar $keygen->( $_ ) } @_;
+ return @_[ sort { $keys[$a] cmp $keys[$b] } 0 .. $#_ ];
+}
+
+=head2 @vals = nsort_by { KEYFUNC } @vals
+
+Similar to C<sort_by> but compares its key values numerically.
+
+=cut
+
+sub nsort_by(&@)
+{
+ my $keygen = shift;
+
+ my @keys = map { local $_ = $_; scalar $keygen->( $_ ) } @_;
+ return @_[ sort { $keys[$a] <=> $keys[$b] } 0 .. $#_ ];
+}
+
+=head2 @vals = rev_sort_by { KEYFUNC } @vals
+
+=head2 @vals = rev_nsort_by { KEYFUNC } @vals
+
+Similar to C<sort_by> and C<nsort_by> but returns the list in the reverse
+order. Equivalent to
+
+ @vals = reverse sort_by { KEYFUNC } @vals
+
+except that these functions are slightly more efficient because they avoid
+the final C<reverse> operation.
+
+=cut
+
+sub rev_sort_by(&@)
+{
+ my $keygen = shift;
+
+ my @keys = map { local $_ = $_; scalar $keygen->( $_ ) } @_;
+ return @_[ sort { $keys[$b] cmp $keys[$a] } 0 .. $#_ ];
+}
+
+sub rev_nsort_by(&@)
+{
+ my $keygen = shift;
+
+ my @keys = map { local $_ = $_; scalar $keygen->( $_ ) } @_;
+ return @_[ sort { $keys[$b] <=> $keys[$a] } 0 .. $#_ ];
+}
+
+=head2 $optimal = max_by { KEYFUNC } @vals
+
+=head2 @optimal = max_by { KEYFUNC } @vals
+
+Returns the (first) value from C<@vals> that gives the numerically largest
+result from the key function.
+
+ my $tallest = max_by { $_->height } @people
+
+ use File::stat qw( stat );
+ my $newest = max_by { stat($_)->mtime } @files;
+
+In scalar context, the first maximal value is returned. In list context, a
+list of all the maximal values is returned. This may be used to obtain
+positions other than the first, if order is significant.
+
+If called on an empty list, an empty list is returned.
+
+For symmetry with the C<nsort_by> function, this is also provided under the
+name C<nmax_by> since it behaves numerically.
+
+=cut
+
+sub max_by(&@)
+{
+ my $code = shift;
+
+ return unless @_;
+
+ local $_;
+
+ my @maximal = $_ = shift @_;
+ my $max = $code->( $_ );
+
+ foreach ( @_ ) {
+ my $this = $code->( $_ );
+ if( $this > $max ) {
+ @maximal = $_;
+ $max = $this;
+ }
+ elsif( wantarray and $this == $max ) {
+ push @maximal, $_;
+ }
+ }
+
+ return wantarray ? @maximal : $maximal[0];
+}
+
+*nmax_by = \&max_by;
+
+=head2 $optimal = min_by { KEYFUNC } @vals
+
+=head2 @optimal = min_by { KEYFUNC } @vals
+
+Similar to C<max_by> but returns values which give the numerically smallest
+result from the key function. Also provided as C<nmin_by>
+
+=cut
+
+sub min_by(&@)
+{
+ my $code = shift;
+
+ return unless @_;
+
+ local $_;
+
+ my @minimal = $_ = shift @_;
+ my $min = $code->( $_ );
+
+ foreach ( @_ ) {
+ my $this = $code->( $_ );
+ if( $this < $min ) {
+ @minimal = $_;
+ $min = $this;
+ }
+ elsif( wantarray and $this == $min ) {
+ push @minimal, $_;
+ }
+ }
+
+ return wantarray ? @minimal : $minimal[0];
+}
+
+*nmin_by = \&min_by;
+
+=head2 @vals = uniq_by { KEYFUNC } @vals
+
+Returns a list of the subset of values for which the key function block
+returns unique values. The first value yielding a particular key is chosen,
+subsequent values are rejected.
+
+ my @some_fruit = uniq_by { $_->colour } @fruit;
+
+To select instead the last value per key, reverse the input list. If the order
+of the results is significant, don't forget to reverse the result as well:
+
+ my @some_fruit = reverse uniq_by { $_->colour } reverse @fruit;
+
+=cut
+
+sub uniq_by(&@)
+{
+ my $code = shift;
+
+ my %present;
+ return grep {
+ my $key = $code->( local $_ = $_ );
+ !$present{$key}++
+ } @_;
+}
+
+=head2 %parts = partition_by { KEYFUNC } @vals
+
+Returns a key/value list of ARRAY refs containing all the original values
+distributed according to the result of the key function block. Each value will
+be an ARRAY ref containing all the values which returned the string from the
+key function, in their original order.
+
+ my %balls_by_colour = partition_by { $_->colour } @balls;
+
+Because the values returned by the key function are used as hash keys, they
+ought to either be strings, or at least well-behaved as strings (such as
+numbers, or object references which overload stringification in a suitable
+manner).
+
+=cut
+
+sub partition_by(&@)
+{
+ my $code = shift;
+
+ my %parts;
+ push @{ $parts{ $code->( local $_ = $_ ) } }, $_ for @_;
+
+ return %parts;
+}
+
+=head2 %counts = count_by { KEYFUNC } @vals
+
+Returns a key/value list of integers, giving the number of times the key
+function block returned the key, for each value in the list.
+
+ my %count_of_balls = count_by { $_->colour } @balls;
+
+Because the values returned by the key function are used as hash keys, they
+ought to either be strings, or at least well-behaved as strings (such as
+numbers, or object references which overload stringification in a suitable
+manner).
+
+=cut
+
+sub count_by(&@)
+{
+ my $code = shift;
+
+ my %counts;
+ $counts{ $code->( local $_ = $_ ) }++ for @_;
+
+ return %counts;
+}
+
+=head2 @vals = zip_by { ITEMFUNC } \@arr0, \@arr1, \@arr2,...
+
+Returns a list of each of the values returned by the function block, when
+invoked with values from across each each of the given ARRAY references. Each
+value in the returned list will be the result of the function having been
+invoked with arguments at that position, from across each of the arrays given.
+
+ my @transposition = zip_by { [ @_ ] } @matrix;
+
+ my @names = zip_by { "$_[1], $_[0]" } \@firstnames, \@surnames;
+
+ print zip_by { "$_[0] => $_[1]\n" } [ keys %hash ], [ values %hash ];
+
+If some of the arrays are shorter than others, the function will behave as if
+they had C<undef> in the trailing positions. The following two lines are
+equivalent:
+
+ zip_by { f(@_) } [ 1, 2, 3 ], [ "a", "b" ]
+ f( 1, "a" ), f( 2, "b" ), f( 3, undef )
+
+The item function is called by C<map>, so if it returns a list, the entire
+list is included in the result. This can be useful for example, for generating
+a hash from two separate lists of keys and values
+
+ my %nums = zip_by { @_ } [qw( one two three )], [ 1, 2, 3 ];
+ # %nums = ( one => 1, two => 2, three => 3 )
+
+(A function having this behaviour is sometimes called C<zipWith>, e.g. in
+Haskell, but that name would not fit the naming scheme used by this module).
+
+=cut
+
+sub zip_by(&@)
+{
+ my $code = shift;
+
+ @_ or return;
+
+ my $len = 0;
+ scalar @$_ > $len and $len = scalar @$_ for @_;
+
+ return map {
+ my $idx = $_;
+ $code->( map { $_[$_][$idx] } 0 .. $#_ )
+ } 0 .. $len-1;
+}
+
+=head2 $arr0, $arr1, $arr2, ... = unzip_by { ITEMFUNC } @vals
+
+Returns a list of ARRAY references containing the values returned by the
+function block, when invoked for each of the values given in the input list.
+Each of the returned ARRAY references will contain the values returned at that
+corresponding position by the function block. That is, the first returned
+ARRAY reference will contain all the values returned in the first position by
+the function block, the second will contain all the values from the second
+position, and so on.
+
+ my ( $firstnames, $lastnames ) = unzip_by { m/^(.*?) (.*)$/ } @names;
+
+If the function returns lists of differing lengths, the result will be padded
+with C<undef> in the missing elements.
+
+This function is an inverse of C<zip_by>, if given a corresponding inverse
+function.
+
+=cut
+
+sub unzip_by(&@)
+{
+ my $code = shift;
+
+ my @ret;
+ foreach my $idx ( 0 .. $#_ ) {
+ my @slice = $code->( local $_ = $_[$idx] );
+ $#slice = $#ret if @slice < @ret;
+ $ret[$_][$idx] = $slice[$_] for 0 .. $#slice;
+ }
+
+ return @ret;
+}
+
+=head2 @vals = extract_by { SELECTFUNC } @arr
+
+Removes elements from the referenced array on which the selection function
+returns true, and returns a list containing those elements. This function is
+similar to C<grep>, except that it modifies the referenced array to remove the
+selected values from it, leaving only the unselected ones.
+
+ my @red_balls = extract_by { $_->color eq "red" } @balls;
+
+ # Now there are no red balls in the @balls array
+
+This function modifies a real array, unlike most of the other functions in this
+module. Because of this, it requires a real array, not just a list.
+
+This function is implemented by invoking C<splice()> on the array, not by
+constructing a new list and assigning it. One result of this is that weak
+references will not be disturbed.
+
+ extract_by { !defined $_ } @refs;
+
+will leave weak references weakened in the C<@refs> array, whereas
+
+ @refs = grep { defined $_ } @refs;
+
+will strengthen them all again.
+
+=cut
+
+sub extract_by(&\@)
+{
+ my $code = shift;
+ my ( $arrref ) = @_;
+
+ my @ret;
+ for( my $idx = 0; $idx < scalar @$arrref; ) {
+ if( $code->( local $_ = $arrref->[$idx] ) ) {
+ push @ret, splice @$arrref, $idx, 1, ();
+ }
+ else {
+ $idx++;
+ }
+ }
+
+ return @ret;
+}
+
+=head2 @vals = weighted_shuffle_by { WEIGHTFUNC } @vals
+
+Returns the list of values shuffled into a random order. The randomisation is
+not uniform, but weighted by the value returned by the C<WEIGHTFUNC>. The
+probabilty of each item being returned first will be distributed with the
+distribution of the weights, and so on recursively for the remaining items.
+
+=cut
+
+sub weighted_shuffle_by(&@)
+{
+ my $code = shift;
+ my @vals = @_;
+
+ my @weights = map { $code->( local $_ = $_ ) } @vals;
+
+ my @ret;
+ while( @vals > 1 ) {
+ my $total = 0; $total += $_ for @weights;
+ my $select = int rand $total;
+ my $idx = 0;
+ while( $select >= $weights[$idx] ) {
+ $select -= $weights[$idx++];
+ }
+
+ push @ret, splice @vals, $idx, 1, ();
+ splice @weights, $idx, 1, ();
+ }
+
+ push @ret, @vals if @vals;
+
+ return @ret;
+}
+
+=head2 @vals = bundle_by { BLOCKFUNC } $number, @vals
+
+Similar to a regular C<map> functional, returns a list of the values returned
+by C<BLOCKFUNC>. Values from the input list are given to the block function in
+bundles of C<$number>.
+
+If given a list of values whose length does not evenly divide by C<$number>,
+the final call will be passed fewer elements than the others.
+
+=cut
+
+sub bundle_by(&@)
+{
+ my $code = shift;
+ my $n = shift;
+
+ my @ret;
+ for( my ( $pos, $next ) = ( 0, $n ); $pos < @_; $pos = $next, $next += $n ) {
+ $next = @_ if $next > @_;
+ push @ret, $code->( @_[$pos .. $next-1] );
+ }
+ return @ret;
+}
+
+=head1 TODO
+
+=over 4
+
+=item * XS implementations
+
+These functions are currently all written in pure perl. Some at least, may
+benefit from having XS implementations to speed up their logic.
+
+=item * Merge into L<List::Util> or L<List::MoreUtils>
+
+This module shouldn't really exist. The functions should instead be part of
+one of the existing modules that already contain many list utility functions.
+Having Yet Another List Utilty Module just worsens the problem.
+
+I have attempted to contact the authors of both of the above modules, to no
+avail; therefore I decided it best to write and release this code here anyway
+so that it is at least on CPAN. Once there, we can then see how best to merge
+it into an existing module.
+
+=back
+
+=head1 AUTHOR
+
+Paul Evans <leonerd@leonerd.org.uk>
+
+=cut
+
+0x55AA;
projects / kivitendo-erp.git / commitdiff