title: SUM still includes suppressed values
body: <p>I've got a report that includes some limited duplicate information, there are multiple dates possible, but I want the dollar values to display on only the first item.</p>
  
  <p>IE:</p>
  
  <blockquote>
    <p>Item 1 - Aug 3, 2010 - Cost $1000<br>
    Item 1 - Aug 4, 2010 - (Cost suppressed)<br>
    Item 2 - Aug 3, 2010 - $100<br>
    Item 3 - Aug 4, 2010 - $200</p>
  </blockquote>
  
  <p>When this is summed, it should display as $1,300, but instead it displays as $2,300.</p>
  
  <p>I have suppressed the cost section by using a formula:</p>
  
  <pre><code>(
  if (Previous({MyReportData;1.MyItemId}) = {MyReportData;1.MyItemId}) then
      true
  else
      false
  )
  </code></pre>
  
  <p>This formula works fine.</p>
  
  <p>I have tried to create a formula to perform a custom SUM which will exclude the duplicated items, but it keeps saying "This field cannot be summarized.</p>
  
  <p>Any ideas?</p>