/// <summary>
/// Returns a new DataFrame with duplicate rows removed, considering only the subset of columns.
/// Reference to https://github.com/apache/spark/blob/branch-1.4/python/pyspark/sql/dataframe.py, dropDuplicates(self, subset=None)
/// </summary>
/// <param name="subset">drop duplicated rows on these columns.</param>
/// <returns>A new DataFrame with duplicate rows removed.</returns>
public DataFrame DropDuplicates(string[] subset = null)
{
return((subset == null || subset.Length == 0) ?
new DataFrame(dataFrameProxy.DropDuplicates(), sparkContext) :
new DataFrame(dataFrameProxy.DropDuplicates(subset), sparkContext));
}