Dynamic nested columns?

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HTML

PHP

CodeIgniter

I am trying to build a dynamic table wherein the columns can be split upon a click. For example, if you click on Split on column 1 in layer 1, column 1 will have two child columns = 2nd layer. When you click on split again in layer 1, one column will be added in layer 2, so on and so forth. However, now I am stuck with how to determine the right colspan depending on the maximum value set by the column with the highest number of child columns.

In the block of code here, I am simply loading data from the database. Data is passed from a model to the view where the table is created.

What I have tried:

So far this is what I have:

<table border=1>
      <tr>
      <?php
        $parentcols = array();
        $maxcolspan = 0;

        //loop through parent columns in layer 1
        foreach($parentcoldata as $parentkey)
        {
          $children = array();

          foreach($childcoldata as $childcol)
          {
          //check if the current child col is a child of the current parent col
            if ($childcol->parentcol_id == $parentkey->id)
            {
                $curchild = array("childname" => $childcol->name, "layer_id" => $childcol->layer_id);
                $children[$childcol->id] = $curchild;
            }
           
          }
          
          //know number of children of current parent column
          $childnum = count($children);
          if ($childnum == 0) {unset($children); echo "Unset";}

          //set colspan based on column with the highest number of children
          if ($childnum > $maxcolspan)
          {
            $maxcolspan = $childnum;
          }
          
          //save the details about the parent column
          $parent = array("name" => $parentkey->name,
                          "child" => $childnum,
                          "children" => $children,
                          "id" => $parentkey->id
                        );
        }

        //print row for parent columns - 1st layer
        for ($i=1; $i<=count($parentcols); $i++) {
            echo '<th id="parentcol'.$parentcols[$i]['id'].'" colspan='.$parentcols[$i]['child'].' style="padding: 5px">'.$parentcols[$i]['name'].'<br />'.
            '<a href="">Edit</a> <br />'.
            '<a href="">Delete</a> <br />'.
            '<a href="">Split</a>'.
            '</th>';
        }
        ?>
      </tr>

      <?php
      //this is where i attempt to print the child columns
      for ($index = 1; $index <= $maxcolspan-1; $index++)
      {
        echo "<tr>";

          foreach($parentcols as $parentcolid => $value) //$parentcolid = key/id
          {
            //loop through children columns
            foreach($value['children'] as $children => $child)
            {
              if ($child['layer_id'] == $index){
                  echo '<td id="'.$children.'" style="padding:5px">'.$child['childname'].
                  '<a href="">Edit</a> <br />'.
                  '<a href="">Delete</a> <br />'.
                  '<a href="" parent-id="someparentid">Split</a>'
                  .'</td>';
              }

            }
          }
          echo "</tr>";
        }
         ?>
    </table>

But with this code, the child columns (3rd layer) of the child columns in the 2nd layer no longer get included.

I am stuck and not sure what I am missing.

Table structure:
columns[^]