title: Unable to sum grouped values correctly using RDLC
body: <p>Suppose my data source is a table of normalized data where each row represents a truckload of grain harvested from a farm field like this.</p>
  
  <pre><code>Field Acres Bushels
  A     50    500
  A     50    600
  B     40    550
  B     40    600
  B     40    500
  C     50    500
  C     50    450
  </code></pre>
  
  <p>I would like my RDLC report to give a summary of this information as follows:</p>
  
  <pre><code>Field    Acres Total Bushels
  A        50    1100
  B        40    1650
  C        50     950
  Totals  140    3600
  </code></pre>
  
  <p>I've tried a couple of different approaches (grouping on Field and grouping on both Field and Acres) but in each case I get the wrong total 320 for the total acres for my three fields. </p>
  
  <p>I'm currently using a single level of grouping which groups on both Field and Acres.  I then add a total row, in which I would like to display the sum of the <em>grouped values</em> for acres, but it seems that I'm unable to use <a href="https://msdn.microsoft.com/en-us/library/dd255256.aspx" rel="nofollow">scoping</a> to accomplish this, since it is illegal to refer to an inner scope from an outer one.  Specifically, I get an error if I try <code>Sum(Fields!Acres.Value, "Field")</code> because the grouping on farm field is <em>inside</em> the overall totals grouping.</p>
  
  <p>It also seems to be illegal to use an aggregate on a ReportItem.  That is, if I name the textbox containing acres, say 'txtAcres', the expression <code>Sum(ReportItem!txtAcres.Value)</code> is not allowed in my totals row. </p>
  
  <p>Please note: I believe that any solution that involves summing <em>distinct</em> values will give the incorrect total acres of 90 (since we have two fields with exactly 50 acres)</p>