title: Log values by SFrame column
body: <p>Please, can anybody tell me, how I can take logarithm from every value in <a href="http://graphlab.com/products/create/docs/generated/graphlab.SFrame.html" rel="noreferrer">SFrame</a>, graphlab (or <a href="http://pandas.pydata.org/pandas-docs/dev/generated/pandas.DataFrame.html" rel="noreferrer">DataFrame</a>, pandas) column, without to iterate through the whole length of the SFrame column? 
  I specially interest on similar functionality, like by <a href="http://graphlab.com/products/create/docs/graphlab.data_structures.html" rel="noreferrer">Groupby Aggregators</a> for the log-function. Couldn't find it someself...</p>
  
  <p><strong>Important:</strong> Please, I don't interest for the <code>for-loop</code> iteration for the whole length of the column. I only interest for specific function, which transform <em>all</em> values to the log-values for the whole column.</p>
  
  <p>I'm also very sorry, if this function is in the manual. Please, just give me a link...</p>