NAME

Tie::RangeHash - Allows hashes to associate values with a range of keys

REQUIREMENTS

Algorithm::SkipList is required. Otherwise it uses standard modules.

SYNOPSIS

use Tie::RangeHash;

tie %hash, 'Tie::RangeHash';

$hash{'A,C'} = 1;
$hash{'D,F'} = 2;
$hash{'G,K'} = 3;

$hash{'E'};           # returns '2'
$hash{'BB'};          # returns '1'

$hash{'KL'};          # returns nothing ('undef')

There is also an object-oriented interface:

$hash = new Tie::RangeHash;

$hash->add('A,C', 1);
$hash->add('G,I', 2);

$hash->fetch('H');    # returns '2'

DESCRIPTION

This module allows hashes to associate a value with a range of keys rather than a single key.

For example, you could pass date ranges to the hash and then query it with a specific date, like so:

$cost{'1999-12-15,2000-01-14'} = 150;
$cost{'2000-01-15,2000-02-14'} = 103;
$cost{'2000-02-15,2000-03-14'} =  97;

and then query the cost on a specific date:

$this_cost = $cost{'2000-02-08'};

Numeric key ranges can also be used:

tie %hash, 'Tie::RangeHash', {
  Type => Tie::RangeHash::TYPE_NUMBER
};

$hash{'1.4,1.8'}      = 'Jim';
$hash{'1.0,1.399999'} = 'Ned';
$hash{'1.800001,2.0'} = 'Boo';

Custom comparison routines to support alternate datatypes can be implemented by specifying a new node type for Algorithm::SkipList.

Object-Oriented Interface

Tie::RangeHash has an object-oriented interface as an alternative to using a tied hash.

new

Creates a new object.

$obj = Tie::RangeHash->new( %attr );

%attr is a hash containing the attributes described above.

add

Adds a new key/value pair to the object.

$obj->add( $key, $value );

$key may be a string value in the form of low,high (for example, "Samantha,Selma").

fetch

$value = $obj->fetch( $key );

Returns the value associated with $key. ($key may be in the form of low,high or any key between low and high.)

If they key range overlaps multiple keys, it will return a fatal error. In such cases, use "fetch_overlap".

fetch_overlap

@values = $obj->fetch_overlap("$low,$high");

Retrieves multiple values associated with a range of keys between $low and $high. Capable of fetching values from overlapping keys.

See "KNOWN ISSUES" for more information about overlapping keys.

fetch_key

$real_key = $obj->fetch_key( $key );

($real_key, $value) = $obj->fetch( $key );

Like "fetch", but it returns the key range that was matched rather than the value. If it is called in an array context, it will return the key and value.

key_exists

if ($obj->key_exists( $key )) { .. }

Returns c<true> if $key has been defined (even if the value is undef). ($key is in the same form as is used by the "fetch" method.)

clear

$obj->clear();

Deletes all keys and values defined in the object.

remove

$value = $obj->remove( $key );

Deletes the $key from the object and returnes the associated value. ($key is in the same form as is used by the fetch method.) If $key is not the exact low,high range, a warning will be emitted.

first_key

$key = $obj->first_key();

Returns the first.

next_key

$key = $obj->next_key($last_key);

Returns the next key in the iteration.

Implementation Notes

Internally, the hash uses skip lists. Skip lists are an alternative to binary trees. For more information, see Algorithm::SkipList.

Future versions may be changed to use something else that is more efficient.

KNOWN ISSUES

The is a new version of the module and has behaves differently compared to older versions. This is due to using the Algorithm::SkipList module for maintaining the underlying data rather than re-implementing it. While this improves the maintainability with the code, it increases incompatability with previous versions.

Some of the changes include:

Overlapping keys cause fatal errors instead of warnings

Because the key comparison is now performed in the skip list node, there is no obvious way for it to give a warning and return a meaningful result. So instead the code dies. If you code relies on the possibility of using overlapping keys, then it may be more appropriate to have it test the code:

eval {
  $hash{'111,999'} = $value;
};

This error can also occur by merely testing a hash, so it is important to run some checks if you are testing hash ranges:

eval {
  if ($hash{'111,999'} == $value) { ... }
}

Another option is to use "fetch_overlap" instead.

Keys can be redefined

Nodes can now be redefined. For example:

$hash{'1,3'} = $value;
...
$hash{'1,3'} = $new_value;
...
$hash{'2'}   = $new_value;

Note that a range is no longer required.

Non-range keys can be added.

When inserting a key, $hash{'x'} will be treated like $hash{'x,x'}.

Open-ended ranges are allowed.

Open ended ranges are now supported. So the following can be added:

$hash{',10'} = $upper_bound;
$hash{'11,'} = $lower_bound;

Note that once open-ended ranges are defined, they are permenently open-ended unless the final range is deleted. Thus,

$hash{'12,13'}

refers to the key "11,".

Array references can no longer be keys.

The following is not supported anymore:

$hash{ \@array ) = $value;

warnings no longer registered.

Warning registration is no longer used. This may change in the future.

Custom separators and comparisons are not supported.

Only commas can be used as separators.

To customize separators and comparisons, you will have to specify a custom Algorithm::SkipList::Node method.

See the Changes file for a more complete list of changes and incompatabilities.

If your code does not rely on these quirks, then you should be able to substitute with no problems.

SEE ALSO

A module with similar functionality for numerical values is Array::IntSpan.

Algorithm::SkipList for more information on skip lists.

AUTHOR

Robert Rothenberg <rrwo at cpan.org>

Acknowledgements

Charles Huff <charleshuff atdecisionresearch.com> for suggestions and bug reports.

Sam Tregar <sam at tregar.com> for optimization suggestions.

Various Perl Monks http://www.perlmonks.org for advice and code snippets.

Suggestions and Bug Reporting

Feedback is always welcome. Please use the CPAN Request Tracker at http://rt.cpan.org to submit bug reports.

LICENSE

Copyright (C) 2000-2008 Robert Rothenberg. All rights reserved. This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.