title: PHPExcel rows grouping
body: <p>I have a one-to-many like array.</p>
  
  <p>Structure example:</p>
  
  <pre><code> [
     [
      InvoiceID,
      [
        InvoiceEntry1_label,
        InvoiceEntry2_label
      ],
      [
        InvoiceEntry1_value,
        InvoiceEntry2_value
      ],
      Total
     ],
     [
      InvoiceID,
      [
        InvoiceEntry1_label,
        InvoiceEntry2_label
      ],
      [
        InvoiceEntry1_value,
        InvoiceEntry2_value
      ],
      Total
     ],
     and so on
   ]
  </code></pre>
  
  <p>How can I group rows using PHPExcel, such that after sorting in Excel, rows which belong to an Invoice will stick together?</p>
  
  <p>Do not confuse with Excel outlining and grouping functionality, for which rows won't stick together after sort.</p>
  
  <p>I already know how to use PHPExcel. A simple example or a documentation reference will do as an answer. I couldn't find one myself.</p>