title: Have a Crystal Reports formula convert numeric strings to values, but leave non-numeric blank/null
body: <p>I have a string field that mostly contains numeric decimal values, but sometimes contains values like "&lt;0.10" or "HEMOLYSIS".</p>
  
  <p>I want to use a formula to convert these numeric value strings to values, leaving non-values blank (null).</p>
  
  <pre><code>if isNumeric({a_omgang.omg_resultat}) then
      toNumber({a_omgang.omg_resultat})
  </code></pre>
  
  <p>returns 0 for all non-numeric values, which makes it hard to calculate e.g. average or mean, or to count the number of values. (The latter can of course be achieved by using a running total count with <code>isNumeric</code> evaluation formula.)</p>
  
  <p>Any suggestions how I can get the formula to work as I want?</p>
  
  <p>Edit: I want the value to be blank (null), not just turn of visibility if non-numeric.</p>