NYCPHP Meetup

[Kenneth Downs]

Johathan,

Have you considered putting the nodes into one array, and the arcs into a
second?

$nodes = array('a'=>array(..info..),'b'=>array(..info..));

$arcs = array(array('a','b'),array('b','a'))

This allows each node's info to be stored only once, and allows you to
then treat the arcs cleanly, allowing or disallowing any combo you may
choose.

You may have to write a little of your code to walk through things, but
you'll have complete integrity and control.

> I'm trying to formulate a question out of this. If there isn't one here,
> I hope the read is interesting.
> My goal is to create the simplest efficient graph data structures - that
> allow for cycles.
>
> The reason one would want cycles in a graph is the following:
> a->b
> and
> b->a
> (or b->a again with another arc (also known as a hypergraph))
> or
> a->a
>
>  where '->' is an arc
> Even if the arcs are labled, the data in 'a' is something I don't want
> to duplicate.
>
> I am using php version 4.3.11
>
> If I try to do this with a simple php array:
>
>     $a = array();
>     $b = array();
>
>     $a['b'] = & $b;
>     $b['a'] = & $a;
>
>     print_r($a);
>
> Array
> (
>     [a] => Array
>         (
>             [b] => Array
>                 (
>                     [a] => Array
>  *RECURSION*
>                 )
>
>         )
>
> )
>
>
> I get this recursion error. Or, perhaps this is not an error at all. But
> I can't seem to use this function:
>
>     function recursive_print($array)
>     {
>         foreach($array as $key => $value)
>         {
>             if (is_array($value))
>             {
>                 echo $key .' <hr /> ' .recursive_print($value);
>             }
>             else
>             {
>                 echo 'end'.$value;
>             }
>         }
>     }
>
> So I went to the PEAR site - http://pear.php.net/package/Structures_Graph
> This pear package doesn't throw any errors but it also seems to balk  -
> although I am not sure the *RECURSION* will affect functionality
>
>
>     include 'Structures/Graph.php';
>     $directedGraph =& new Structures_Graph(true);
>     $nodeOne =& new Structures_Graph_Node();
>     $nodeTwo =& new Structures_Graph_Node();
>
>
>     $directedGraph->addNode(&$nodeOne);
>     $directedGraph->addNode(&$nodeTwo);
>
>
>     $nodeOne->connectTo($nodeTwo);
>     $nodeTwo->connectTo($nodeOne);
>
>
> Inside the code I found a comment about the Zend engine before the data
> structure procedes to iteratively loop through the the nodes to see if
> there are duplicates.
>             /*
>              ZE1 equality operators choke on the recursive cycle
> introduced by the _graph field in the Node object.
>              So, we'll check references the hard way
>             */
>
> Even so, print_r produces many recursion warnings.
>
> Maybe I am just trying to use a hammer for a screwdriver. But can anyone
> offer any insight here?
>
> Thanks,
>
> - Jonathan Hendler
>
>
>
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-- 
Kenneth Downs
Secure Data Software
631-379-0010
ken at secdat.com
PO Box 708
East Setauket, NY 11733