NAME

Array::Heap - treat perl arrays as heaps (priority queues)

SYNOPSIS

use Array::Heap;

DESCRIPTION

There are a multitude of heap and heap-like modules on CPAN, you might want to search for /Heap/ and /Priority/ to find many. They implement more or less fancy datastructures that might well be what you are looking for.

This module takes a different approach: It exports functions (i.e. no object orientation) that are loosely modeled after the C++ STL's heap functions. They all take an array as argument, just like perl's built-in functions "push", "pop" etc.

The implementation itself is in C for maximum speed.

FUNCTIONS

All of the following functions are being exported by default.

make_heap @heap (\@)

        Reorders the elements in the array so they form a heap, with the
        lowest value "on top" of the heap (corresponding to the first array
        element).

make_heap_lex @heap (\@)

        Just like "make_heap", but in string comparison order instead of
        numerical comparison order.

make_heap_cmp { compare } @heap (&\@)

Just like "make_heap", but takes a custom comparison function.

push_heap @heap, $element, ... (\@@)

Adds the given element(s) to the heap.

push_heap_lex @heap, $element, ... (\@@)

        Just like "push_heap", but in string comparison order instead of
        numerical comparison order.

push_heap_cmp { compare } @heap, $element, ... (&\@@)

Just like "push_heap", but takes a custom comparison function.

pop_heap @heap (\@)

Removes the topmost (lowest) heap element and repairs the heap.

pop_heap_lex @heap (\@)

        Just like "pop_heap", but in string comparison order instead of
        numerical comparison order.

pop_heap_cmp { compare } @heap (&\@)

Just like "pop_heap", but takes a custom comparison function.

splice_heap @heap, $index (\@$)

        Similar to "pop_heap", but removes and returns the element at index
        $index.

splice_heap_lex @heap, $index (\@$)

        Just like "splice_heap", but in string comparison order instead of
        numerical comparison order.

splice_heap_cmp { compare } @heap, $index (&\@$)

Just like "splice_heap", but takes a custom comparison function.

adjust_heap @heap, $index (\@$)

        Assuming you have only changed the element at index $index, repair
        the heap again. Can be used to remove elements, replace elements,
        adjust the priority of elements and more.

adjust_heap_lex @heap, $index (\@$)

        Just like "adjust_heap", but in string comparison order instead of
        numerical comparison order.

adjust_heap_cmp { compare } @heap, $index (&\@$)

Just like "adjust_heap", but takes a custom comparison function.

COMPARISON FUNCTIONS
All the functions come in two flavours: one that uses the built-in comparison function and one that uses a custom comparison function.

The built-in comparison function can either compare scalar numerical values (string values for *_lex functions), or array refs. If the elements to compare are array refs, the first element of the array is used for comparison, i.e.

1, 4, 6

will be sorted according to their numerical value,

[1 => $obj1], [2 => $obj2], [3 => $obj3]

will sort according to the first element of the arrays, i.e. "1,2,3".

The custom comparison functions work similar to how "sort" works: $a and $b are set to the elements to be compared, and the result should be greater than zero then $a is greater than $b, 0 otherwise. This means that you cna use the same function as for sorting the array, but you could also use a simpler function that just does "$a > $b".

The first example above corresponds to this comparison "function":

{ $a <=> $b }

And the second example corresponds to this:

{ $a->[0] <=> $b->[0] }

Unlike "sort", the default sort is numerical and it is not possible to use normal subroutines.

BUGS

• Numerical comparison is always done using floatingpoint, which usually has less precision than a 64 bit integer that perl might use for integers internally, resulting in precision loss on the built-in comparison.
• This module does not work with tied or magical arrays or array elements, and, in fact, will even crash when you use those.
• This module can leak memory (or worse) when your comparison function exits unexpectedly (e.g. "last") or throws an exception, so do not do that.

AUTHOR

     Marc Lehmann <schmorp@schmorp.de>
     http://home.schmorp.de/