title: R package compilation with dependency on data.table
body: <p>I am trying to create an R package with a function using the <code>J</code> of data.table.
  When I run <code>R CMD check</code>, I have a NOTE : no visible global function definition for 'J'
  although I've added data.table as a dependency in the DESCRIPTION file.</p>
  
  <blockquote>
    <p>Package: rfPred<br>
    Type: Package<br>
    Title: Assign rfPred functional prediction scores to a missense variants list<br>
    Version: 1.0<br>
    Date: 2013-03-14<br>
    Author: me<br>
    Maintainer:me<br>
    Depends: data.table<br>
    [..]  </p>
  </blockquote>
  
  <p>I've tried to use another function of the data.table package in the package I want to create, but I haven't the same problem as for J.</p>
  
  <p>Do you have a solution ?</p>