title: remove degree symbol from numeric values in data frame
body: <p>I've had some temperature measurements in .csv format and am trying to analyse them in R. For some reason the data files contain temperature with degree C following the numeric value. Is there a way to remove the degree C symbol and return the numeric value? I though of producing an example here but did not know how to generate a degree symbol in a string in R. Anyhow, this is what the data looks like:</p>
  
  <pre><code>&gt; head(mm)
               dateTime Temperature
  1 2009-04-23 17:01:00   15.115 °C
  2 2009-04-23 17:11:00   15.165 °C
  3 2009-04-23 17:21:00   15.183 °C
  </code></pre>
  
  <p>where the class of mm[,2] is 'factor'</p>
  
  <p>Can anyone suggest a method for converting the second column to 15.115 etc?</p>