Michael Anton Dines Zedeler

NAME

Data::Dmap - just like map, but on deep data structures

VERSION

Version 0.08.

SYNOPSIS

This module provides the single function dmap which carries out a map-like operation on deep data structures.

    use Data::Dmap;

    my $foo = {
        cars => [ 'ford', 'opel', 'BMW' ],
        birds => [ 'cuckatoo', 'ostrich', 'frigate' ],
        handler => sub { print "barf\n" }
    };

    # This removes all keys named 'cars'    
    my($bar) = dmap { delete $_->{cars} if ref eq 'HASH'; $_ } $foo;

    # This replaces arrays with the number of elements they contains
    my($other) = dmap { $_ = scalar @$_ if ref eq 'ARRAY'; $_ } $foo;

    use Data::Dumper;
    print Dumper $other;
    #
    # Prints
    # {
    #    birds => 3,
    #    handler => sub { "DUMMY" }
    # }
    # (Data::Dumper doesn't dump subs)

    $other->{handler}->();
    # Prints
    # barf

EXPORTS

dmap (always exported) - the dmap function that does deep in-place mapping
cut (optional) - a function for stopping recursion.

SUBROUTINES

dmap

This function works like map - it takes an expression followed by a list, evaluates the expression on each member of the list and returns the result.

The only difference is that any references returned by the expression will also be traversed and passed to the expression once again, thus making it possible to make deep traversal of any data structure.

Objects (references blessed to something) are just traversed as if they weren't blessed.

Examples

Delete all hash references

    use Data::Dmap;
    use Data::Dump 'pp';
    
    pp dmap { return $_ unless ref eq 'HASH'; return; } 1, 'foo', [ { a => 1 }, 2];
    
    # Prints:
    # (1, "foo", [2])
    

Delete every odd number

    use Data::Dmap;
    use Data::Dump 'pp';
    
    pp dmap { return if $_ % 2; $_ } [ 1 .. 10 ];

    # Prints:
    # [2, 4, 6, 8, 10]

Replace all hash refs with some $object of class thingy.

    use Data::Dmap;
    use Data::Dump 'pp';
    
    pp dmap { return bless $_, 'thingy' if ref eq 'HASH'; $_ } [ 1, "hello", { a => 1 } ];
    
    # Prints:
    # [1, "hello", bless({ a => 1 }, "thingy")]

dmap understands what you want, if you return nothing (as opposed to undef) when evaluating the expression for a hash key:

    use Data::Dmap;
    use Data::Dump 'pp;

    my $characters = { main => 'pooh', secondary => 'piglet' };
    pp dmap { return if $_ eq "piglet"; $_ } $characters;
    
    # Prints:
    # { main => "pooh" }
    

Because the output from the expression is being traversed, you can use dmap to generate data structures:

    use Data::Dmap;
    use Data::Dump 'pp';
    
    my $height = 3;
    pp dmap { if(ref eq 'HASH' and $height--) { $_->{a} = {height => $height} } $_ } {};
    
    # Prints:
    # {
    #     a => {
    #         a => {
    #             a => { 
    #                 height => 0
    #             },
    #             height => 1
    #         },
    #         height => 2
    #     }
    # }
    # (My own formatting above.)

cut

The cut routine stops recursion at any point and returns any data as it is in place of the current node.

Examples

    use Data::Dmap 'cut';
    use Data::Dump 'pp';
    
    my $deep = {
        level => 1,
        data  => {
            level => 2,
            data => {
                level => 3
            }
        }
    };
    
    pp dmap { cut('stop') if ref eq 'HASH' and $_->{level} == 2} $deep;

    # Prints:
    #
    # { data => { data => "stop", level => 2 }, level => 1 }
                       
                

AUTHOR

Michael Zedeler, <michael@zedeler.dk>

BUGS

If you find a bug, please consider helping to fix the bug by doing this:

  • Fork Data::Dmap from http://github.com/mzedeler/Data-Dmap

  • Write a test case in the t directory, commit and push it.

  • Fix the bug or (if you don't know how to fix it), report the bug

Bugs and feature requests can be reported through the web interface at http://github.com/mzedeler/Data-Dmap/issues. I may not be notified, so send me a mail too.

SUPPORT

You can find documentation for this module with the perldoc command.

    perldoc Data::Dmap

You can also look for information at:

SEE ALSO

Data::Rmap, Data::Visitor, Data::Transformer, Data::Visitor, Data::Walk.

TODO

Some kind of option making it possible to traverse objects with Class::MOP metaclasses, so we can avoid breaking encapsulation.
Options to provide more information about the current node to the callback handler, such as path, depth and data types. Should not affect performance if not used.

LICENSE AND COPYRIGHT

Copyright 2010 Michael Zedeler.

This program is free software; you can redistribute it and/or modify it under the terms of either: the GNU General Public License as published by the Free Software Foundation; or the Artistic License.

See http://dev.perl.org/licenses/ for more information.