iterstats 0.7.0

Statistics for rust iterators.
Documentation 
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//! Caculate the variance.

use crate::{welford_online::welford_online, Iterstats};

/// Calculate the variance of an iterator.
pub trait Variance<A = Self>: Sized {
    /// The type of the output.
    type Output;

    /// Calculate the variance.
    fn variance<I>(iter: I) -> Self::Output
    where
        I: Iterator<Item = A>;
}

macro_rules! variance_impl {
    ($typ:ty) => {
        impl Variance for $typ {
            type Output = $typ;

            fn variance<I>(iter: I) -> Self::Output
            where
                I: Iterator<Item = Self>,
            {
                let wo = welford_online(iter);
                wo.sum_of_squares / wo.count
            }
        }

        impl Variance for &$typ {
            type Output = $typ;

            fn variance<I>(iter: I) -> Self::Output
            where
                I: Iterator<Item = Self>,
            {
                iter.map(|i| *i).variance()
            }
        }
    };
}

variance_impl!(f64);
variance_impl!(f32);

#[cfg(test)]
mod tests {
    use super::*;
    use paste::paste;

    macro_rules! test_variance {
        ( $name:ident: $iterty:ty as $iter:expr; into_iter => nan ) => {
            paste! {
                #[test]
                fn [<$name _into_iter >]() {
                    let var = <$iterty>::variance($iter.into_iter());
                    assert!(var.is_nan());
                }
            }
        };
        ( $name:ident: $iterty:ty as $iter:expr; iter => nan ) => {
            paste! {
                #[test]
                fn [<$name _iter >]() {
                    let var = <&$iterty>::variance($iter.iter());
                    assert!(var.is_nan());
                }
            }
        };
        ( $name:ident: $iterty:ty as $iter:expr => nan ) => {
            test_variance!($name: $iterty as $iter ; into_iter => nan);
            test_variance!($name: $iterty as $iter ; iter => nan);
        };
        ( $name:ident: $iterty:ty as $iter:expr; into_iter => $expected:expr ) => {
            paste! {
                #[test]
                fn [<$name _into_iter >]() {
                    let var = <$iterty>::variance($iter.into_iter());
                    assert_eq!(var, $expected);
                }
            }
        };
        ( $name:ident: $iterty:ty as $iter:expr; iter => $expected:expr ) => {
            paste! {
                #[test]
                fn [<$name _iter >]() {
                    let var = <&$iterty>::variance($iter.iter());
                    assert_eq!(var, $expected);
                }
            }
        };
        ( $name:ident: $iterty:ty as $iter:expr => $expected:expr ) => {
            test_variance!($name: $iterty as $iter ; into_iter => $expected);
            test_variance!($name: $iterty as $iter ; iter => $expected);
        };
    }

    test_variance!(f64: f64 as [1.0, 2.0, 3.0, 4.0] => 1.25);
    test_variance!(f64_max: f64 as [f64::MAX, f64::MAX] => 0.0);
    test_variance!(f64_min: f64 as [f64::MIN, f64::MIN] => 0.0);
    test_variance!(f64_minmax: f64 as [f64::MAX, f64::MIN] => f64::NEG_INFINITY);
    test_variance!(f64_nan: f64 as [1.0, 2.0, f64::NAN, 3.0, 4.0] => nan);
    test_variance!(f64_inf: f64 as [1.0, 2.0, f64::INFINITY, 3.0, 4.0] => nan);
    test_variance!(f64_neg_inf: f64 as [1.0, 2.0, f64::NEG_INFINITY, 3.0, 4.0] => nan);
    test_variance!(f32: f32 as [1.0, 2.0, 3.0, 4.0] => 1.25);
    test_variance!(f32_max: f32 as [f32::MAX, f32::MAX] => 0.0);
    test_variance!(f32_min: f32 as [f32::MIN, f32::MIN] => 0.0);
    test_variance!(f32_minmax: f32 as [f32::MAX, f32::MIN] => f32::NEG_INFINITY);
    test_variance!(f32_nan: f32 as [1.0, 2.0, f32::NAN, 3.0, 4.0] => nan);
    test_variance!(f32_inf: f32 as [1.0, 2.0, f32::INFINITY, 3.0, 4.0] => nan);
    test_variance!(f32_neg_inf: f32 as [1.0, 2.0, f32::NEG_INFINITY, 3.0, 4.0] => nan);
}