/// <summary>
/// Groups the DataFrame using the specified columns, so we can run aggregation on them.
/// </summary>
/// <param name="firstColumnName">first column name - required</param>
/// <param name="otherColumnNames">other column names - optional</param>
/// <returns></returns>
public GroupedData GroupBy(string firstColumnName, params string[] otherColumnNames)
{
var scalaGroupedDataReference = dataFrameProxy.GroupBy(firstColumnName, otherColumnNames);
return(new GroupedData(scalaGroupedDataReference, this));
}