Method take_needed

datafusion/expr-common/src/groups_accumulator.rs:42–56

Removes the number of rows from `v` required to emit the right number of rows, returning a `Vec` with elements taken, and the remaining values in `v`. This avoids copying if Self::All

(&self, v: &mut Vec<T>)

    ///
    /// This avoids copying if Self::All
    pub fn take_needed<T>(&self, v: &mut Vec<T>) -> Vec<T> {
        match self {
            Self::All => {
                // Take the entire vector, leave new (empty) vector
                std::mem::take(v)
            }
            Self::First(n) => {
                // get end n+1,.. values into t
                let mut t = v.split_off(*n);
                // leave n+1,.. in v
                std::mem::swap(v, &mut t);
                t
            }
        }
    }
}

/// `GroupsAccumulator` implements a single aggregate (e.g. AVG) and