Dominique Dumont

NAME

Array::IntSpan - Handles arrays of scalars or objects using IntSpan techniques

SYNOPSIS

  use Array::IntSpan;

  my $foo = Array::IntSpan->new([0, 59, 'F'], [60, 69, 'D'], [80, 89, 'B']);

  print "A score of 84% results in a ".$foo->lookup(84).".\n";
  unless (defined($foo->lookup(70))) {
    print "The grade for the score 70% is currently undefined.\n";
  }

  $foo->set_range(70, 79, 'C');
  print "A score of 75% now results in a ".$foo->lookup(75).".\n";

  $foo->set_range(0, 59, undef);
  unless (defined($foo->lookup(40))) {
    print "The grade for the score 40% is now undefined.\n";
  }

  $foo->set_range(87, 89, 'B+');
  $foo->set_range(85, 100, 'A');
  $foo->set_range(100, 1_000_000, 'A+');

DESCRIPTION

Array::IntSpan brings the speed advantages of Set::IntSpan (written by Steven McDougall) to arrays. Uses include manipulating grades, routing tables, or any other situation where you have mutually exclusive ranges of integers that map to given values.

The new version of Array::IntSpan is also able to consolidate the ranges by comparing the adjacent values of the range. If 2 adjacent values are identical, the 2 adjacent ranges are merged.

Ranges of objects

Array::IntSpan can also handle objects instead of scalar values.

But for the consolidation to work, the payload class must overload the "", eq and == operators to perform the consolidation comparisons.

When a get_range method is called to a range of objects, it will return a new range of object referencess. These object references points to the objects stored in the original range. In other words the objects contained in the returned range are not copied.

Thus if the user calls a methods on the objects contained in the returned range, the method is actually invoked on the objects stored in the original range.

When a get_range method is called on a range of objects, several things may happen:

  • The get_range spans empty slots. By default the returned range will skip the empty slots. But the user may provide a callback to create new objects (for instance). See details below.

  • The get_range splits existing ranges. By default, the split range will contains the same object reference. The user may provide callback to perform the object copy so that the split range will contains different objects. See details below.

Ranges specified with integer fields

  • Array::IntSpan::IP is also provided with the distribution. It lets you use IP addresses in any of three forms (dotted decimal, network string, and integer) for the indices into the array. See the POD for that module for more information. See Array::IntSpan::IP for details.

  • Array::IntSpan::Fields is also provided with the distribution. It let you specify an arbitrary specification to handle ranges with strings made of several integer separared by dots (like IP addresses of ANSI SS7 point codes). See Array::IntSpan::Fields for details.

METHODS

new (...)

The new method takes an optional list of array elements. The elements should be in the form [start_index, end_index, value]. They should be in sorted order and there should be no overlaps. The internal method _check_structure will be called to verify the data is correct. If you wish to avoid the performance penalties of checking the structure, you can use Data::Dumper to dump an object and use that code to reconstitute it.

clear

Clear the range.

set_range (start, end, value [, code ref] )

This method takes three parameters - the start_index, the end_index, and the value. If you wish to erase a range, specify undef for the value. It properly deals with overlapping ranges and will replace existing data as appropriate. If the new range lies after the last existing range, the method will execute in O(1) time. If the new range lies within the existing ranges, the method executes in O(n) time, where n is the number of ranges. It does not consolidate contiguous ranges that have the same value.

If you have a large number of inserts to do, it would be beneficial to sort them first. Sorting is O(n lg(n)), and since appending is O(1), that will be considerably faster than the O(n^2) time for inserting n unsorted elements.

The method returns 0 if there were no overlapping ranges and 1 if there were.

The optional code ref is called back when an existing range is split. For instance if the original range is [0,10,$foo_obj] and set_range is called with [5,7,$bar_obj'], the callback will be called twice:

 $callback->(0, 4,$foo_obj)
 $callback->(8,10,$foo_obj)

It will be the callback responsability to make sure that the range 0-4 and 7-10 holds 2 different objects.

get_range (start, end [, filler | undef , copy_cb [, set_cb]])

This method returns a range (actually an Array::IntSpan object) from start to end.

If start and end span empty slot in the original range, get_range will skip the empty slots. If a filler value is provided, get_range will fill the slots with it.

 original range    : [2-4,X],[7-9,Y],[12-14,Z]
 get_range(3,8)    : [3-4,X],[7-8,Y]
 get_range(2,10,f) : [3-4,X],[5-6,f],[7-8,Y]

If the filler parameter is a CODE reference, the filler value will be the one returned by the sub ref. The sub ref is invoked with (start,end), i.e. the range of the empty span to fill (get_range(5,6) in the example above). When handling object, the sub ref can invoke an object constructor.

If start or end split an original range in 2, the default behavior is to copy the value or object ref contained in the original range:

 original range     : [1-4,X]
 split range        : [1-1,X],[2-2,X],[3-4,X]
 get_range(2)       : [2-2,X]

If the original range contains object, this may lead to disapointing results. In the example below the 2 ranges contains references (obj_a) that points to the same object:

 original range     : [1-4,obj_a]
 split range        : [1-1,obj_a],[2-2,obj_a],[3-4,obj_a]
 get_range(2)       : [2-2,obj_a]

Which means that invoking a method on the object returned by get_range(2) will also be invoked on the range 1-4 of the original range which may not be what you want.

If get_range is invoked with a copy parameter (actually a code reference), the result of this routine will be stored in the split range outside of the get_range:

 original range     : [1-4,X]
 get_range(2)       : [2-2,X]
 split range        : [1-1,copy_of_X],[2-2,X],[3-4,copy_of_X]

When dealing with object, the sub ref should provide a copy of the object:

 original range     : [1-4,obj_a]
 get_range(2)       : [2-2,obj_a]
 split range        : [1-1,obj_a1],[2-2,obj_a],[3-4,obj_a2]

Note that the obj_a contained in the split range and the obj_a contained in the returned range point to the same object.

The sub ref is invoked with (start,end,obj_a) and is expected to return a copy of obj_a that will be stored in the split ranges. In the example above, 2 different copies are made: obj_a1 and obj_a2.

Last, a 3rd callback may be defined by the user: the set_cb. This callback will be used when the range start or end that holds an object changes. In the example above, the set_cb will be called this way:

 $obj_a->&$set_cb(2,2) ;

As a matter of fact, the 3 callback can be used in the same call. In the example below, get_range is invoked with 3 subs refs: \&f,\&cp,\&set:

 original range     : [1-4,obj_a],[7-9,obj_b]
 get_range(3-8,...) : [3-4,obj_a],[5-6,obj_fill],[7-8,obj_b]
 split range        : [1-2,obj_a1], [3-4,obj_a],[5-6,obj_fill],
                      [7-8,obj_b],[9-9,obj_b1]

To obtain this, get_range will perform the following calls:

 $obj_fill = &f ;
 $obj_a1 = &cp(5,6,obj_a);
 &set(3,4,$obj_a) ;
 $obj_b = &cp(9,9,obj_b) ;
 &set(7-8,obj_b) ; 

lookup( index )

This method takes as a single parameter the index to look up. If there is an appropriate range, the method will return the associated value. Otherwise, it returns undef.

get_element( element_number )

Returns an array containing the Nth range element:

 ( start, end, value )

consolidate( bottom, top , [ set_cb ] )

This function scan the range from the range index bottom to top and compare the values held by the adjacent ranges. If the values are identical, the adjacent ranges are merged.

The comparision is made with the == operator. Objects stored in the range must overload the == operator. If not, the comparison will be made with the standard stringification of an object and the merge will never happen.

If provided, the set_cb will be invoked on the contained object after 2 ranges are merged.

For instance, if the "$obj_a" eq "$obj_b":

 original range         : [1-4,obj_a],[5-9,obj_b]
 consolidate(0,1,\&set) : [1-9,obj_a]

And consolidate will perform this call:

 &$set(1,9,obj_a) ;

AUTHOR

  • Toby Everett, teverett@alascom.att.com

  • Dominique Dumont, dominique.dumont@hp.com

Copyright (c) 2000 Toby Everett. Copyright (c) 2003-2004 Dominique Dumont. All rights reserved. This program is free software.

This module is distributed under the Artistic License. See http://www.ActiveState.com/corporate/artistic_license.htm or the license that comes with your perl distribution.




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