Method variance

datafusion/expr-common/src/statistics.rs:164–172

Extracts the variance value of this uncertain quantity, depending on its distribution: - A [`Uniform`] distribution's interval determines its variance value, which is calculable by the formula `(upper - lower) ^ 2 / 12`. - An [`Exponential`] distribution's variance is calculable by the formula `1 / (λ ^ 2)`, where `λ` is the (non-negative) rate. - A [`Gaussian`] distribution's variance is specifie

(&self)

    /// - A [`Generic`] distribution _may_ have it explicitly, or this information
    ///   may be absent.
    pub fn variance(&self) -> Result<ScalarValue> {
        match &self {
            Uniform(u) => u.variance(),
            Exponential(e) => e.variance(),
            Gaussian(g) => Ok(g.variance.clone()),
            Bernoulli(b) => b.variance(),
            Generic(u) => Ok(u.variance.clone()),
        }
    }

    /// Extracts the range of this uncertain quantity, depending on its
    /// distribution: