Aggregation

Expr.count	Aggregation operation that counts the non null values of the given column in the group.
Expr.first	Get the first element.
Expr.last	Get the last element.
Expr.len	Aggregation operation that counts the rows in the group.
Expr.max	Aggregation operation that finds the maximum value in the group.
Expr.mean	Aggregation operation that finds the mean of the values in the group.
Expr.median	Aggregation operation that finds the median of the values in the group.
Expr.min	Aggregation operation that finds the minimum value in the group.
Expr.n_unique	Aggregation operation that counts the unique values of the given column in the group.
Expr.rank	Compute the rank of the element values.
Expr.sum	Aggregation operation that sums the values in the group.
TableFrame.group_by	Perform a group by on the TableFrame.