title: do dplyr mutate support runif
body: <p>I want to generate normally distributed random numbers as a column using mutate. I tried using <code>runif()</code> but it throws error on a large scale data. </p>
  
  <pre><code>extract_grp &lt;- extract_grp %&gt;%
  mutate(rand = runif(sdf_nrow(extract_grp)))
  glimpse(extract_grp)
  </code></pre>
  
  <p>The error that am getting is:</p>
  
  <blockquote>
    <p>Error: org.apache.spark.sql.AnalysisException: Undefined function:
    'RUNIF'. This function is neither a registered temporary function nor
    a permanent function registered in the database 'temp_data'.; line 1
    pos 101   at org.apache.spark.sql.catalyst.catalog.SessionCatalog.failFunctionLookup(SessionCatalog.scala:999)
      at org.apache.spark.sql.hive.HiveSessionCatalog.lookupFunction0(HiveSessionCatalog.scala:202)
      at org.apache.spark.sql.hive.HiveSessionCatalog.lookupFunction(HiveSessionCatalog.scala:174)
      at org.apache.spark.sql.catalyst.analysis.Analyzer$ResolveFunctions$$anonfun$apply$13$$anonfun$applyOrElse$6$$anonfun$applyOrElse$39.apply(Analyzer.scala:897)</p>
  </blockquote>