Notice: Undefined index (how do I fix this?)

Hello,

This script works but gives me a load of notices:
         Undefined index

I am running PHP Version 5.1.5.


Please help!
Thanks.

<?php
$pagecontents = null;
$keys = null;
$freqall = null;
$freqarray = null;
$freqarray2 = null;
$freqarray3 = null;

$commonwords = 'a an about';

$sitecontents = "This is a test and only a test.";

$parsearray[] = $sitecontents;
$parsestring = strtolower(join($parsearray," "));
$parsestring = str_replace (",", "", $parsestring);
$parsestring = str_replace ("\n", "", $parsestring);
$parsestring = str_replace (")", "", $parsestring);
$parsestring = str_replace ("(", "", $parsestring);
$parsestring = str_replace (".", "", $parsestring);
$parsestring = str_replace ("'", "", $parsestring);
$parsestring = str_replace ('"', "", $parsestring);

$commonarray = split(" ",$commonwords);

for ($i=0; $i<count($commonarray); $i++) {
   $parsestring = str_replace (" ".$commonarray[$i]." ", " ", $parsestring);
}

$parsestring = str_replace ("  ", " ", $parsestring);
$parsestring = str_replace ("  ", " ", $parsestring);
$parsestring = str_replace ("  ", " ", $parsestring);

$wordsarray = split(" ",$parsestring);

for ($i=0; $i<count($wordsarray); $i++) {
   $word = $wordsarray[$i];
   if ($freqarray[$word]) {
       $freqarray[$word] += 1;
   } else {
       $freqarray[$word]=1;
   }
}

arsort($freqarray);

$i=0;
while (list($key, $val) = each($freqarray)) {    
   $i++;
   $freqall[$key] = $val;
   if ($i==15) {
      break;
   }
}

for ($i=0; $i<count($wordsarray)-1; $i++) {
   $j = $i+1;
   $word2 = $wordsarray[$i]." ".$wordsarray[$j];
   if ($freqarray2[$word2]) {
       $freqarray2[$word2] += 1;
   } else {
       $freqarray2[$word2]=1;
   }
}

arsort($freqarray2);

$i=0;
while (list($key, $val) = each($freqarray2)) {    
   $i++;
   $freqall[$key] = $val;
   if ($i==4) {
      break;
   }
}

for ($i=0; $i<count($wordsarray)-2; $i++) {
   $j = $i+1;
   $word3 = $wordsarray[$i]." ".$wordsarray[$j]." ".$wordsarray[$j+1];
   if ($freqarray3[$word3]) {
       $freqarray3[$word3] += 1;
   } else {
       $freqarray3[$word3]=1;
   }
}

arsort($freqarray3);

$i=0;
while (list($key, $val) = each($freqarray3)) {    
   $i++;
   $freqall[$key] = $val;
   if ($i==1) {
      break;
   }
}

arsort($freqall);

while (list($key, $val) = each($freqall)) {    
   $pagecontents .= "$key => $val<br>";
   $keys .= $key.", ";
}

chop($keys);

$pagecontents .= $keys;

echo $pagecontents;

?>