title: pandas convert strings to float for multiple columns in dataframe
body: <p>I'm new to pandas and trying to figure out how to convert multiple columns which are formatted as strings to float64's.  Currently I'm doing the below, but it seems like apply() or applymap() should be able to accomplish this task even more efficiently...unfortunately I'm a bit too much of a rookie to figure out how.  Currently the values are percentages formatted as strings like '15.5%'</p>
  
  <pre><code>for column in ['field1', 'field2', 'field3']:
      data[column] = data[column].str.rstrip('%').astype('float64') / 100
  </code></pre>