title: Replace non-numeric values as truly missing in excel
body: <p>I want to use the data analysis toolpack (and perform other analyses) on data which (unintentionally) have strings where there should be numbers.  For example, I might have a column:</p>
  
  <pre><code>0,
  1,
  don't know,
  7
  </code></pre>
  
  <p>I use the following statement to generate a new column:</p>
  
  <pre><code>=IF(ISNUMBER(A1),A1,"")
  </code></pre>
  
  <p>Returning:</p>
  
  <pre><code>0,
  1,
  "",
  7
  </code></pre>
  
  <p>I'm unable to do data analysis on these because of the "".  However, if I just type the following into cells skipping the third row, I am able to do analysis:</p>
  
  <pre><code>0,
  1,
  ,
  7
  </code></pre>
  
  <p>Any tips on how to properly do this replacement using missing values is appreciated.  Thanks,</p>