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# $Id: MultipleFields.pm,v 1.11 2008/07/28 21:53:23 drhyde Exp $ |
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package Sort::MultipleFields; |
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use strict; |
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use warnings; |
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use vars qw($VERSION @EXPORT_OK @ISA); |
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use Scalar::Util qw(reftype); |
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use Exporter; # 5.6's Exporter doesn't export its import function, so |
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# need to do the inheritance dance. Joy. |
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@ISA = qw(Exporter); |
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@EXPORT_OK = qw(mfsort mfsortmaker); |
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$VERSION = '1.01'; |
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=head1 NAME |
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Sort::MultipleFields - Conveniently sort on multiple fields |
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=head1 SYNOPSIS |
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use Sort::MultipleFields qw(mfsort); |
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my $library = mfsort { |
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author => 'ascending', |
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title => 'ascending' |
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} ( |
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{ |
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author => 'Hoyle, Fred', |
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title => 'Black Cloud, The' |
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}, |
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{ |
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author => 'Clarke, Arthur C', |
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title => 'Rendezvous with Rama' |
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}, |
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{ |
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author => 'Clarke, Arthur C', |
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title => 'Islands In The Sky' |
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} |
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); |
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after which C<$library> would be a reference to a list of three hashrefs, |
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which would be (in order) the data for "Islands In The Sky", "Rendezvous |
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with Rama", and "The Black Cloud". |
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=head1 DESCRIPTION |
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This provides a simple way of sorting structured data with multiple fields. |
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For instance, you might want to sort a list of books first by author and |
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within each author sort by title. |
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=head1 EXPORTS |
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The subroutines may be exported if you wish, but are not exported by |
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default. |
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Default-export is bad and wrong and people who do it should be spanked. |
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=head1 SUBROUTINES |
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=head2 mfsort |
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@sorted = mfsort { SORT SPEC } @unsorted; |
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Takes a sort specification and a list (or list-ref) of references to hashes. |
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It returns either a list or a list-ref, depending on context. |
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The sort specification is a block structured thus: |
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{ |
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field1 => 'ascending', |
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field2 => 'descending', |
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field3 => sub { |
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lc($_[0]) cmp lc($_[1]) # case-insensitive ascending |
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}, |
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... |
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} |
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Yes, it looks like a hash. But it's not, it's a block that returns a |
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list, and order matters. |
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The spec is a list of pairs, each consisting of a field to sort on, and |
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how to sort it. How to sort is simply a function that, when given a |
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pair of pieces of data, will return -1, 0 or 1 depending on whether the first |
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argument is "less than", equal to, or "greater than" the second argument. |
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Sounds familiar, doesn't it. As short-cuts for the most common sorts, |
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the following case-insensitive strings will work: |
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=over |
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=item ascending, or asc |
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Sort ASCIIbetically, ascending (ie C<$a cmp $b>) |
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=item descending, or desc |
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Sort ASCIIbetically, descending (ie C<$b cmp $a>) |
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=item numascending, or numasc |
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Sort numerically, ascending (ie C<< $a <=> $b >>) |
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=item numdescending, or numdesc |
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Sort numerically, descending (ie C<< $b <=> $a >>) |
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=back |
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Really old versions |
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of perl might require that you instead pass the sort spec as an |
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anonymous subroutine. |
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mfsort sub { ... }, @list |
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=cut |
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sub mfsort(&@) { |
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my $spec = shift; |
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my @records = @_; |
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@records = @{$records[0]} if(reftype($records[0]) eq 'ARRAY'); |
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(grep { reftype($_) ne 'HASH' } @records) && |
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die(__PACKAGE__."::mfsort: Can only sort hash-refs\n"); |
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my $sortsub = mfsortmaker($spec); |
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@records = sort { $sortsub->($a, $b) } @records; |
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return wantarray() ? @records : \@records; |
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} |
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=head2 mfsortmaker |
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This takes a sort spec subroutine reference like C but returns |
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a reference to a subroutine that you can use with the built-in C |
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function. |
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my $sorter = mfsortmaker(sub { |
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author => 'asc', |
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title => 'asc' |
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}); |
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@sorted = sort $sorter @unsorted; |
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Note that you need to store the generated subroutine in a variable before |
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using it, otherwise the parser gets confused. |
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Using this function to generate functions for C to use should be |
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considered to be experimental, as it can make some versions of perl |
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segfault. It appears to be reliable if you do this: |
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my $sorter = mfsortmaker(...); |
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@sorted = sort { $sorter->($a, $b) } @unsorted; |
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and that's what the C function does internally. |
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=cut |
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sub mfsortmaker { |
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my $spec = shift; |
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my @spec = $spec->(); |
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my $sortsub = sub($$) { 0 }; # default is to not sort at all |
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while(@spec) { # eat this from the end towards the beginning |
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my($spec, $field) = (pop(@spec), pop(@spec)); |
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die(__PACKAGE__."::mfsortmaker: malformed spec after $field\n") |
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unless(defined($spec)); |
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if(!ref($spec)) { # got a string |
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$spec = ($spec =~ /^asc(ending)?$/i) ? sub { $_[0] cmp $_[1] } : |
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($spec =~ /^desc(ending)?$/i) ? sub { $_[1] cmp $_[0] } : |
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($spec =~ /^numasc(ending)?$/i) ? sub { $_[0] <=> $_[1] } : |
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($spec =~ /^numdesc(ending)?$/i) ? sub { $_[1] <=> $_[0] } : |
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die(__PACKAGE__."::mfsortmaker: Unknown shortcut '$spec'\n"); |
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} |
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my $oldsortsub = $sortsub; |
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$sortsub = sub($$) { |
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$spec->($_[0]->{$field}, $_[1]->{$field}) || |
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$oldsortsub->($_[0], $_[1]) |
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} |
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} |
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# extra layer of wrapping seems to prevent segfaults in 5.8.8. WTF? |
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# return $sortsub |
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return sub($$) { |
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# use Data::Dumper;print(map { Dumper($_) } @_);print "\n\n"; |
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$sortsub->(@_) |
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}; |
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} |
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=head1 BUGS, LIMITATIONS and FEEDBACK |
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If you find undocumented bugs please report them either using |
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L or by email. Ideally, I would like to receive |
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sample data and a test file, which fails with the latest version of |
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the module but will pass when I fix the bug. |
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For some unknown reason, passing C a particularly complex subroutine |
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generated using mfsortmaker can sometimes make perl 5.8.8 (and possibly |
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earlier versions) segfault. I *think* I've worked around it, and at least |
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it doesn't happen for me any more, but YMMV. It was something of a |
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Heisenbug so the current fix doesn't fill me with confidence. |
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=cut |
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=head1 SEE ALSO |
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L for sorting data consisting of strings with fixed-length |
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fields in them. |
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=head1 AUTHOR, COPYRIGHT and LICENCE |
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Copyright 2008 David Cantrell Edavid@cantrell.org.ukE |
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This software is free-as-in-speech software, and may be used, |
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distributed, and modified under the terms of either the GNU |
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General Public Licence version 2 or the Artistic Licence. It's |
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up to you which one you use. The full text of the licences can |
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be found in the files GPL2.txt and ARTISTIC.txt, respectively. |
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=head1 CONSPIRACY |
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This module is also free-as-in-mason software. |
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=cut |
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1; |