title: Flysystem/CSV filter a subset of columns
body: <p>Is it possible to filter a subset of columns of a CSV with <a href="http://csv.thephpleague.com/" rel="nofollow">Flysystem CSV</a>?</p>
  
  <p>I know that you can use <code>AbstractCsv::addFilter(callable $callback)</code> to add arbitrary filters, but I don't think you would use this to drop a column.</p>