vortex-array 0.68.0

Vortex in memory columnar data format
Documentation 
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// SPDX-License-Identifier: Apache-2.0
// SPDX-FileCopyrightText: Copyright the Vortex contributors

use std::cmp::Ordering;

use crate::expr::stats::Precision;
use crate::expr::stats::Stat;
use crate::expr::stats::bound::IntersectionResult;
use crate::partial_ord::partial_min;

/// `StatType` define the bound of a given statistic. (e.g. `Max` is an upper bound),
/// this is used to extract the bound from a `Precision` value, (e.g. `p::bound<Max>()`).
pub trait StatType<T> {
    type Bound: StatBound<T>;

    const STAT: Stat;
}

/// `StatBound` defines the operations that can be performed on a bound.
/// The main bounds are Upper (e.g. max) and Lower (e.g. min).
pub trait StatBound<T>: Sized {
    /// Creates a new bound from a Precision statistic.
    fn lift(value: Precision<T>) -> Self;

    /// Converts `Self` back to `Precision<T>`, inverse of `lift`.
    fn into_value(self) -> Precision<T>;

    /// Finds the smallest bound that covers both bounds.
    /// A.k.a. the `meet` of the bound.
    fn union(&self, other: &Self) -> Option<Self>;

    /// Refines the bounds to the most precise estimate we can make for that bound.
    /// If the bounds are disjoint, then the result is `None`.
    /// e.g. `Precision::Inexact(5)` and `Precision::Exact(6)` would result in `Precision::Inexact(5)`.
    /// A.k.a. the `join` of the bound.
    fn intersection(&self, other: &Self) -> Option<IntersectionResult<Self>>;

    /// Returns the exact value from the bound if that value is exact, otherwise `None`.
    fn to_exact(&self) -> Option<&T>;
}

/// This allows a stat with a `Precision` to be interpreted as a bound.
impl<T> Precision<T> {
    /// Applied the stat associated bound to the precision value
    pub fn bound<S: StatType<T>>(self) -> S::Bound {
        S::Bound::lift(self)
    }
}

impl<T: PartialOrd + Clone> StatBound<T> for Precision<T> {
    fn lift(value: Precision<T>) -> Self {
        value
    }

    fn into_value(self) -> Precision<T> {
        self
    }

    fn union(&self, other: &Self) -> Option<Self> {
        self.clone()
            .zip(other.clone())
            .map(|(lhs, rhs)| partial_min(&lhs, &rhs).cloned())
            .transpose()
    }

    fn intersection(&self, other: &Self) -> Option<IntersectionResult<Self>> {
        Some(match (self, other) {
            (Precision::Exact(lhs), Precision::Exact(rhs)) => {
                if lhs.partial_cmp(rhs)? == Ordering::Equal {
                    IntersectionResult::Value(Precision::Exact(lhs.clone()))
                } else {
                    IntersectionResult::None
                }
            }
            (Precision::Exact(exact), Precision::Inexact(inexact))
            | (Precision::Inexact(inexact), Precision::Exact(exact)) => {
                if exact.partial_cmp(inexact)? == Ordering::Less {
                    IntersectionResult::Value(Precision::Inexact(exact.clone()))
                } else {
                    IntersectionResult::Value(Precision::Exact(exact.clone()))
                }
            }
            (Precision::Inexact(lhs), Precision::Inexact(rhs)) => {
                IntersectionResult::Value(Precision::Inexact(partial_min(lhs, rhs)?.clone()))
            }
        })
    }

    fn to_exact(&self) -> Option<&T> {
        match self {
            Precision::Exact(val) => Some(val),
            _ => None,
        }
    }
}