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/

CPAN RT