I couldn't find an example of what I wanted to do, which was dynamically create and handle enumerated variables from a form, so here it is in simplified form:

<?php
echo("<table>");
$counter=0;
for ($a=0;$a<count($timeslots);$a++) {
  echo("<tr>");
  for ($i=0;$i<3;$i++) {
                    $counter++;
                    $fieldwithcounter="fieldname$counter";
                    $var1=$_POST[$fieldwithcounter];
                    $nextfield="second$counter";
                    $var2=$_POST[$nextfield];
                    $thirdfield="lastfield$counter";
                    $var3=$_POST[$thirdfield];
eval("\$grouprow$a.=\"$var1^^$var2^^$var3^^$var4\";");
// creates $grouprow0, $grouprow1, $grouprow2, ...

echo("<td>
    First field
        <input type='text' name='fieldname$counter' value='$var1'><br>

    Second field
      <input type='text' name='second$counter' value='$var2'><br>

    Last field
      <input type='text' name='lastfield$counter' value='$var3'>
      </td>");
  }
echo("</tr>");
}
echo("</table>");
?>