title: Control number of target parquet files
body: <p>I have ~250 folders. Each folders in a day.
  Each folder contains 24 parquet files.
  I need to read them all, run on them a function, and write them after the change of the function.</p>
  
  <p>When writing, I am doing this:</p>
  
  <pre><code>df
    .repartition('date)
    .write
    .partitionBy("date")
    .mode(SaveMode.Overwrite)
    .parquet(outputPath)
  </code></pre>
  
  <p>But this "loses" the original split to 24 parts each date, and writes one file per date. Is there any option to split each day to n parts?</p>