title: SparkR window function
body: <p>I found from <a href="https://issues.apache.org/jira/browse/SPARK-10043" rel="nofollow">JIRA</a> that 1.6 release of <code>SparkR</code> has implemented window functions including <code>lag</code> and <code>rank</code>, but <code>over</code> function is not implemented yet. How can I use window function like <code>lag</code> function without <code>over</code> in <code>SparkR</code>(not the <code>SparkSQL</code> way)? Can someone provide an example?</p>