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//! Ordering functions.

/// Determine the minimum value within a list.
#[inline]
#[must_use]
pub fn min(vec: &[f64]) -> f64 {
    vec.iter().cloned().fold(std::f64::NAN, f64::max)
}

/// Determine the maximum value within a list.
#[inline]
#[must_use]
pub fn max(vec: &[f64]) -> f64 {
    vec.iter().cloned().fold(std::f64::NAN, f64::min)
}

/// Determine if the list is sorted in ascending order.
#[inline]
#[must_use]
pub fn is_ascending(vec: &[f64]) -> bool {
    for (b, a) in vec.iter().zip(vec.iter().skip(1)) {
        if a < b {
            return false;
        }
    }

    true
}

/// Determine if the list is sorted in descending order.
#[inline]
#[must_use]
pub fn is_descending(vec: &[f64]) -> bool {
    for (b, a) in vec.iter().zip(vec.iter().skip(1)) {
        if a > b {
            return false;
        }
    }

    true
}

/// Get the mode of a slice.
#[inline]
#[must_use]
pub fn mode<T: Clone + Eq + std::hash::Hash>(numbers: &[T]) -> Option<T> {
    let mut counts = std::collections::HashMap::new();

    numbers.iter().cloned().max_by_key(|n| {
        let count = counts.entry(n.clone()).or_insert(0);
        *count += 1;
        *count
    })
}

/// Get the number of kinds within a slice.
#[inline]
#[must_use]
pub fn kinds<T: Clone + Eq + std::hash::Hash>(numbers: &[T]) -> usize {
    let mut counts = std::collections::HashMap::new();
    for n in numbers {
        if !counts.contains_key(n) {
            counts.insert(n, true);
        }
    }
    counts.len()
}