/ 
Array-Heap-3.22
River stage one • 2 direct dependents • 3 total dependents
/ Array::Heap

NAME

Array::Heap - treat perl arrays as binary 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 binary 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_idx @heap (\@)

Just like make_heap, but updates the index (see INDEXED OPERATIONS).

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

Just like push_heap, but updates the index (see INDEXED OPERATIONS).

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_idx @heap (\@)

Just like pop_heap, but updates the index (see INDEXED OPERATIONS).

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_idx @heap, $index (\@$)

Just like splice_heap, but updates the index (see INDEXED OPERATIONS).

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_idx @heap, $index (\@$)

Just like adjust_heap, but updates the index (see INDEXED OPERATIONS).

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 can 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.

INDEXED OPERATIONS

The functions whose names end in _idx also "update the index". That means that all elements must be array refs, with the first element being the heap value, and the second value being the array index:

[$value, $index, ...]

This allows you to quickly locate an element in the array when all you have is the array reference.

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.

SEE ALSO

This module has a rather low-level interface. If it seems daunting, you should have a look at Array::Heap::ModifiablePriorityQueue, which is based on this module but provides more and higher-level operations with an object-oriented API which makes it harder to make mistakes.

A slightly less flexible (only numeric weights), but also slightly faster variant of that module can be found as Array::Heap::PriorityQueue::Numeric on CPAN.

AUTHOR AND CONTACT INFORMATION

Marc Lehmann <schmorp@schmorp.de>
http://software.schmorp.de/pkg/Array-Heap