title: How to fix a problem with substract position by grouping on some position
body: <p>In my xslt converter I have to substract some of position from one invoice and show it on group. I don't know how can I do this. Now I have xslt which give me a result in separate position. </p>
  
  <pre><code>&lt;Invoice&gt;
      &lt;P_1&gt;2019.04.30&lt;/P_1&gt;
      &lt;P_2&gt;FV_0660/E/2019&lt;/P_2&gt;
      &lt;P_3&gt;Client&lt;/P_3&gt;
      &lt;P_4&gt;Client Adress&lt;/P_4&gt;
      &lt;P_5&gt;3570.9200&lt;/P_5&gt;
      &lt;P_6&gt;821.3100&lt;/P_6&gt;
      &lt;P_7&gt;4392.23&lt;/P_7&gt;
  &lt;/Invoice&gt;
  &lt;InvoiceRecord typ="G"&gt;
      &lt;P_8&gt;FV_0660/E/2019&lt;/P_8&gt;
      &lt;P_9&gt;Position1&lt;/P_9&gt;
      &lt;P_10&gt;1707.10&lt;/P_10&gt;
      &lt;P_11&gt;2099.73&lt;/P_11&gt;
  &lt;/InvoiceRecord&gt;
  &lt;InvoiceRecord typ="G"&gt;
      &lt;P_8&gt;FV_0660/E/2019&lt;/P_8&gt;
      &lt;P_9&gt;Position2 variable&lt;/P_9&gt;
      &lt;P_10&gt;143.61&lt;/P_10&gt;
      &lt;P_11&gt;176.64&lt;/P_11&gt;
  &lt;/InvoiceRecord&gt;
  &lt;InvoiceRecord typ="G"&gt;
      &lt;P_8&gt;FV_0660/E/2019&lt;/P_8&gt;
      &lt;P_9&gt;Position3&lt;/P_9&gt;
      &lt;P_10&gt;0.00&lt;/P_10&gt;
      &lt;P_11&gt;0.00&lt;/P_11&gt;
  &lt;/InvoiceRecord&gt;
  &lt;InvoiceRecord typ="G"&gt;
      &lt;P_8&gt;FV_0660/E/2019&lt;/P_8&gt;
      &lt;P_9&gt;Position4&lt;/P_9&gt;
      &lt;P_10&gt;1086.47&lt;/P_10&gt;
      &lt;P_11&gt;1336.36&lt;/P_11&gt;
  &lt;/InvoiceRecord&gt;
  &lt;InvoiceRecord typ="G"&gt;
      &lt;P_8&gt;FV_0660/E/2019&lt;/P_8&gt;
      &lt;P_9&gt;Position5 variable&lt;/P_9&gt;
      &lt;P_10&gt;103.46&lt;/P_10&gt;
      &lt;P_11&gt;127.26&lt;/P_11&gt;
  &lt;/InvoiceRecord&gt;
  &lt;InvoiceRecord typ="G"&gt;
      &lt;P_8&gt;FV_0660/E/2019&lt;/P_8&gt;
      &lt;P_9&gt;Position6&lt;/P_9&gt;
      &lt;P_10&gt;384.38&lt;/P_10&gt;
      &lt;P_11&gt;472.79&lt;/P_11&gt;
  &lt;/InvoiceRecord&gt;
  &lt;InvoiceRecord typ="G"&gt;
      &lt;P_8&gt;FV_0660/E/2019&lt;/P_8&gt;
      &lt;P_9&gt;Position7 variable&lt;/P_9&gt;
      &lt;P_10&gt;32.34&lt;/P_10&gt;
      &lt;P_11&gt;39.78&lt;/P_11&gt;
  &lt;/InvoiceRecord&gt;
  &lt;InvoiceRecord typ="G"&gt;
      &lt;P_8&gt;FV_0660/E/2019&lt;/P_8&gt;
      &lt;P_9&gt;Position8&lt;/P_9&gt;
      &lt;P_10&gt;9.87&lt;/P_10&gt;
      &lt;P_11&gt;12.14&lt;/P_11&gt;
  &lt;/InvoiceRecord&gt;
  &lt;InvoiceRecord typ="G"&gt;
      &lt;P_8&gt;FV_0660/E/2019&lt;/P_8&gt;
      &lt;P_9&gt;Position9&lt;/P_9&gt;
      &lt;P_10&gt;103.69&lt;/P_10&gt;
      &lt;P_11&gt;127.54&lt;/P_11&gt;
  &lt;/InvoiceRecord&gt;
  </code></pre>
  
  <p>Now I get result</p>
  
  <pre><code> Position1 1707.10
   Position2 variable 143.61 etc.
  </code></pre>
  
  <p>The result that I need is like this</p>
  
  <pre><code>Positions 3291.51
  PositionsV 279.41
  </code></pre>
  
  <p>I need sum of positions without word variable and second sum with variable. Maybe someone can help me with this problem please.</p>