Function compute_mean

datafusion/expr-common/src/statistics.rs:823–848

(
    op: &Operator,
    left: &Distribution,
    right: &Distribution,
)

    note = "Part of the unused Statistics V2 framework; see https://github.com/apache/datafusion/pull/22071"
)]
pub fn compute_mean(
    op: &Operator,
    left: &Distribution,
    right: &Distribution,
) -> Result<ScalarValue> {
    let (left_mean, right_mean) = (left.mean()?, right.mean()?);

    match op {
        Operator::Plus => return left_mean.add_checked(right_mean),
        Operator::Minus => return left_mean.sub_checked(right_mean),
        // Note the independence assumption below:
        Operator::Multiply => return left_mean.mul_checked(right_mean),
        // TODO: We can calculate the mean for division when we support reciprocals,
        // or know the distributions of the operands. For details, see:
        //
        // <https://en.wikipedia.org/wiki/Algebra_of_random_variables>
        // <https://stats.stackexchange.com/questions/185683/distribution-of-ratio-between-two-independent-uniform-random-variables>
        //
        // Fall back to an unknown mean value for division:
        Operator::Divide => {}
        // Fall back to an unknown mean value for other cases:
        _ => {}
    }
    let target_type = Distribution::target_type(&[&left_mean, &right_mean])?;
    ScalarValue::try_from(target_type)
}

/// Computes the median value for the result of the given binary operation on
/// two unknown quantities represented by its [`Distribution`] objects. Currently,