title: Formula to detect duplicate data in Excel (with a difficult variable!)
body: <p>I need to sanitise a mailing list, and am wondering if anyone knows of a formula to find out the following:</p>
  
  <p>I have an excel spreadsheet with two columns A and B, the formula I need to do is: if [value in column B is duplicated] has [blank in column A] AND [data in column A] then show the value of Column B in a new Column C.</p>
  
  <p>Example of data:</p>
  
  <pre><code>COL A      |    COL B
  11/11/12   |    **name@example.com**
  03/09/11   |    different@example.com
             |    **name@example.com**
  06/01/12   |    anothername@example.com
  </code></pre>
  
  <p>The formula would detect name@example.com is duplicated &amp; it has a date in column A &amp; further on has no value in column A, and therefore displays: name@example.com in Column C.</p>
  
  <p>Hope that makes sense! </p>