groupBy(...args) {
        return groupBy(this, args);
    }
Group DataFrame rows by columns giving a GroupedDataFrame object. See its doc for more examples.
@param {...String} columnNames The columns used for the groupBy.
@returns {GroupedDataFrame} A GroupedDataFrame object.
@example
df.groupBy('column1')
df.groupBy('column1', 'column2')
df.groupBy('column1', 'column2').listGroups()
df.groupBy('column1', 'column2').show()
df.groupBy('column1', 'column2').aggregate((group) => group.count())