I use this script I wrote to process the Abyss log to get the number of unique hits on my site:

<?php

// *** Start Remote Authority Check ***

$myip = "127.0.0.1";

$ra = $_SERVER["REMOTE_ADDR"];
if ($ra <> $myip) { 
	return;
	 }

// *** End Remote Authority Check ***

// Start Display

echo "<center><h3>Stats</h3></center>";

$log_path='..\log\access.log'; // Alter if different
$ct = date("d/M/Y H:i:s");

// Fetch start date and time

$text = fopen($log_path,'r') ;
	$txt = fgets($text);
	$first = strpos($txt,'[')+1;
	$last = strpos($txt,'+')-$first;
	$st = substr($txt,$first,$last);
	$da = substr($st,0,11);
	$ti = substr($st,12,8);
	$dt = "$da $ti";
fclose($text);

// Define Variables (not strictly needed but prevents warnings)

$c = 0;
$f = 0;
$chk = 0;
$txt = 0; // Reset from first use

// Process log file

$txt = fopen($log_path,'r') ;

if ($txt) {
   while (!feof($txt)) {
       $buffer = fgets($txt);
       $string = substr($buffer,0,15);
       if ($f <> 0) { $chk = $f; }
       $f = rtrim($string," -");
       if ($f != $chk and $chk <> 0) {$c++; }

}
   fclose($txt);
}
if ($dt == 0) {$dt = $ct; }
	echo "<center><b>Current Time $ct</b></center><br>";
	echo "<center><b>Hits from $dt = $c</b></center><br>";

?>

It is designed to only display locally (hence the $_SERVER check) and it works pretty well. It performs a simple line by line read of the log and increments a counter each time it reads a new ip address. This is good but it falls down when there is more than one user online at the same time. It doesn't stop working but it does increment the counter for the same user twice (or more) because of the fact that it reads the log sequentially.
I want to be able to perform another check to see if the current IP is the same as one previously used elsewhere (non sequentially) in the log. I imagine I would need to use some kind of array to achieve this but am having great difficulty getting my head around "array" variables. Last time I used arrays was in BASIC many years ago.
Sorry about this being a bit long winded but I needed to explain the problem properly. Anyone have any ideas how to improve it and how to solve the problem I am faced with? The stats I get from it are only for my own info and not displayed to users online.