cast

fun <T> DataFrame<*>.cast(): DataFrame<T>
inline fun <reified T> DataFrame<*>.cast(verify: Boolean = true): DataFrame<T>
fun <T> DataRow<*>.cast(): DataRow<T>
inline fun <reified T> DataRow<*>.cast(verify: Boolean = true): DataRow<T>
fun <C> ColumnSet<*>.cast(): ColumnSet<C>
fun <T, G> GroupBy<*, *>.cast(): GroupBy<T, G>