# NAME List::Breakdown - Build sublist structures matching conditions # VERSION Version 0.17 # SYNOPSIS use List::Breakdown 'breakdown'; ... my @words = qw(foo bar baz quux wibble florb); my $cats = { all => sub { 1 }, has_b => sub { m/ b /msx }, has_w => sub { m/ w /msx }, length => { 3 => sub { length == 3 }, 4 => sub { length == 4 }, long => sub { length > 4 }, }, has_ba => qr/ba/msx, }; my %filtered = breakdown $cats, @words; This puts the following structure in `%filtered`: ( all => ['foo', 'bar', 'baz', 'quux', 'wibble', 'florb'], has_b => ['bar', 'baz', 'wibble', 'florb'], has_w => ['wibble'], length => { 3 => ['foo', 'bar', 'baz'], 4 => ['quux'], long => ['wibble', 'florb'], }, has_ba => ['bar', 'baz'], ) # DESCRIPTION This module assists you in making a _breakdown_ of a list, copying and filtering its items into a structured bucket layout according to your specifications. Think of it as a syntax for [`grep`](https://metacpan.org/pod/perlfunc#grep-BLOCK-LIST) that returns named and structured results from one list. It differs from the excellent [List::Categorize](https://metacpan.org/pod/List::Categorize) in the use of references to define each category, and in not requiring only one final category for any given item; an item can end up in the result set for more than one filter. If you want to divide or _partition_ your list so that each item can only appear in one category, you may want either [List::MoreUtils](https://metacpan.org/pod/List::MoreUtils#Partitioning) or possibly [Set::Partition](https://metacpan.org/pod/Set::Partition) instead. # SUBROUTINES/METHODS ## `breakdown(\%spec, @items)` This is the only exportable subroutine. Given a hash reference structure and a list of items, it applies each of the referenced values as tests, returning a new hash in the same structure with the references replaced with the matching items, in the same way as [`grep`](https://metacpan.org/pod/perlfunc#grep-BLOCK-LIST). There are two shortcut syntaxes for a value in the `\%spec` structure: - `ARRAY` If the referenced array has exactly two items, it will be interpreted as defining numeric bounds `[lower,upper)` for its values. `undef` can be used to denote negative or positive infinity. Any other number of items is a fatal error. - `Regexp` This will be interpreted as a pattern for the list items to match. Additionally, if the value is a `HASH` reference, it can be used to make a sub-part of the structure, as demonstrated in the `length` key of the example `\%spec` given in [SYNOPSIS](#synopsis). # EXAMPLES ## Collecting troublesome records Suppose you have a list of strings from a very legacy system that you need to regularly check for problematic characters, alerting you to problems with an imperfect Perl parser: my @records = ( "NEW CUSTOMER John O''Connor\r 2017-01-01", "RETURNING CUSTOMER\tXah Zhang 2016-01-01", "CHECK ACCOUNT Pierre d'Alun 2016-12-01", "RETURNING CUSTOMER Aaron Carter 2016-05-01" ); You could have a bucket structure like this, using the **pattern syntax**, which catches certain error types you've seen before for review: my %buckets = ( bad_whitespace => qr/ [\r\t] /msx, apostrophes => qr/ ' /msx, double_apostrophes => qr/ '' /msx, not_ascii => qr/ [^[:ascii:]] /msx }; Applying the bucket structure like so: my %results = breakdown \%buckets, @records; The result set would look like this: my %expected = ( bad_whitespace => [ "NEW CUSTOMER John O''Connor\r 2017-01-01", "RETURNING CUSTOMER\tXah Lee 2016-01-01" ], apostrophes => [ "NEW CUSTOMER John O''Connor\r 2017-01-01", 'CHECK ACCOUNT Pierre d\'Alun 2016-12-01' ], double_apostrophes => [ "NEW CUSTOMER John O''Connor\r 2017-01-01" ], not_ascii => [ ] ); Notice that some of the lines appear in more than one list, and that the `not_ascii` bucket is empty, because none of the items matched it. ## Monitoring system check results Suppose you ran a list of checks with your monitoring system, and now you have a list of `HASH` references with keys describing each check and its outcome: my @checks = ( { hostname => 'webserver1', status => 'OK', }, { hostname => 'webserver2', status => 'CRITICAL', }, { hostname => 'webserver3', status => 'WARNING', }, { hostname => 'webserver4', status => 'OK', } ); You would like to break the list down by status. You would lay out your buckets like so, using the **subroutine syntax**: my %buckets = ( ok => sub { $_->{status} eq 'OK' }, problem => { warning => sub { $_->{status} eq 'WARNING' }, critical => sub { $_->{status} eq 'CRITICAL' }, unknown => sub { $_->{status} eq 'UNKNOWN' }, }, ); And apply them like so: my %results = breakdown \%buckets, @checks; For our sample data above, this would yield the following structure in `%results`: ( ok => [ { hostname => 'webserver1', status => 'OK' }, { hostname => 'webserver4', status => 'OK' } ], problem => { warning => [ { hostname => 'webserver3', status => 'WARNING' } ], critical => [ { hostname => 'webserver2', status => 'CRITICAL' } ], unknown => [] } ) Note the extra level of `HASH` references beneath the `problem` key. ## Grouping numbers by size Suppose you have a list of numbers from your volcanic activity reporting system, some of which might be merely worrisome, and some others an emergency, and they need to be filtered to know where to send them: my @numbers = ( 1, 32, 3718.4, 0x56, 0777, 3.14, -5, 1.2e5 ); You could filter them into buckets like this, using the **interval syntax**: an `ARRAY` reference with exactly two elements: lower bound (inclusive) first, upper bound (exclusive) second: my $filters = { negative => [ undef, 0 ], positive => { small => [ 0, 10 ], medium => [ 10, 100 ], large => [ 100, undef ], }, }; Applying the bucket structure like so: my %filtered = breakdown $filters, @numbers; The result set would look like this: my %expected = ( negative => [ -5 ] positive => { small => [ 1, 3.14 ], medium => [ 32, 86 ], large => [ 3_718.4, 511, 120_000 ] }, ); Notice that you can express infinity or negative infinity as `undef`. Note also this is a numeric comparison only. # AUTHOR Tom Ryder `` # DIAGNOSTICS - `HASH reference expected for first argument` The first argument that `breakdown()` saw wasn't the hash reference it expects. That's the only format a spec is allowed to have. - `Reference expected for '%s'` The value for the named key in the spec was not a reference, and one was expected. - `Unhandled ref type %s for '%s'` The value for the named key in the spec is of a type that makes no sense to this module. Legal reference types are `ARRAY`, `CODE`, `HASH`, and `Regexp`. # DEPENDENCIES - Perl 5.6.0 or newer - [base](https://metacpan.org/pod/base) - [Carp](https://metacpan.org/pod/Carp) - [Exporter](https://metacpan.org/pod/Exporter) # CONFIGURATION AND ENVIRONMENT None required. # INCOMPATIBILITIES None known. # BUGS AND LIMITATIONS Definitely. This is a very early release. Please report any bugs or feature requests to `tom@sanctum.geek.nz`. # SUPPORT You can find documentation for this module with the **perldoc** command. perldoc List::Breakdown You can also look for information at: - RT: CPAN's request tracker (report bugs here) [http://rt.cpan.org/NoAuth/Bugs.html?Dist=List-Breakdown](http://rt.cpan.org/NoAuth/Bugs.html?Dist=List-Breakdown) - AnnoCPAN: Annotated CPAN documentation [http://annocpan.org/dist/List-Breakdown](http://annocpan.org/dist/List-Breakdown) - CPAN Ratings [http://cpanratings.perl.org/d/List-Breakdown](http://cpanratings.perl.org/d/List-Breakdown) - Search CPAN [http://search.cpan.org/dist/List-Breakdown/](http://search.cpan.org/dist/List-Breakdown/) # LICENSE AND COPYRIGHT Copyright (C) 2017 Tom Ryder This program is free software; you can redistribute it and/or modify it under the terms of the Artistic License (2.0). 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