Ken Dozier wrote:
> Does in_array() use a search algorithm (i.e., binary search), or does it
> check sequentially each element in the array?
>
> I am using in_array() within a while{} loop to check query results against
> an access-list array to produce a third array containing items that
> successfully passed the comparison test. Because the two starting arrays in
> the worst-case scenario can have 8,000 items each, the loop is timing out.
> Advice or alternative methods are appreciated.
>
> Code Sample:
> <?php
> function check_results($results, $access_list)
> { # Check for $results in array $access_list and
> # add matches to array $match.
>
> $result = false;
> $match = array();
>
> while ($r = mysql_fetch_row($results))
> { if ( in_array($r[0], $access_list) )
> { $match[] = $r; }
> }
>
> if ( count($match) > 0 ) { $result = $match; }
>
> return $result;
> }
> ?>
Hi Ken,
Since arrays are hash tables in PHP, it would be far faster to use an
associative array. How?
$access_list = array_flip($access_list);
then
if (isset($access_list[$r[0]]))
However, this sounds more like a design issue with the SQL that creates
$results. You can do the in_array natively in SQL with "WHERE
otherthing IN ("thing1", "thing2",...)" which would automatically filter
out the non-matches in a far more efficient manner, perhaps increasing
requests per second by an exponential factor. Of course, if
$access_list is from external input (user input), you will need to
escape the output, make sure you have the proper encoding, etc. so you
can avoid SQL injection attacks and other nastiness, but that is another
topic.
If you are getting $access_list from another query, you could also try
using a sub-query as in "WHERE otherthing IN (SELECT ...)" but this of
course assumes you are are using MySQL >= version 4.1.
In any case, you are definitely going to want to revisit the design of
your queries before even starting with reworking your PHP.
Good luck,
Greg
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