iterstats 0.7.0

Statistics for rust iterators.
Documentation 
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//! Calculate the z-score.

use std::ops::{Div, Sub};

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

/// Calculate the z-score of each item of an iterator.
pub trait ZScore<A = Self>: Sized {
    /// The type of the output
    type Output;

    /// Calculate the z-score of each item.
    fn zscore<I>(iter: I) -> ZScoreIter<Self::Output>
    where
        I: Iterator<Item = A> + Clone;
}

/// Iterator for calculating the z-score of each item of the iterator.
#[derive(Debug, Clone)]
pub struct ZScoreIter<T> {
    iter: std::vec::IntoIter<T>,
    mean: T,
    stddev: T,
}

impl<T> Iterator for ZScoreIter<T>
where
    T: Copy + Sub<Output = T> + Div<Output = T>,
{
    type Item = T;

    fn next(&mut self) -> Option<Self::Item> {
        self.iter.next().map(|v| (v - self.mean) / self.stddev)
    }
}

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

            fn zscore<I>(iter: I) -> ZScoreIter<Self::Output>
            where
                I: Iterator<Item = Self> + Clone,
            {
                let wo = welford_online(iter.clone());
                let itertype = iter.collect::<Vec<_>>();
                ZScoreIter {
                    iter: itertype.into_iter(),
                    mean: wo.mean,
                    stddev: (wo.sum_of_squares / wo.count).sqrt(),
                }
            }
        }

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

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

zscore_impl!(f64);
zscore_impl!(f32);

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

    macro_rules! test_zscore {
        ( $name:ident: $iterty:ty as $iter:expr; into_iter => nan ) => {
            paste! {
                #[test]
                fn [<$name _into_iter >]() {
                    assert!(<$iterty>::zscore($iter.into_iter()).all(|v| v.is_nan()));
                }
            }
        };
        ( $name:ident: $iterty:ty as $iter:expr; iter => nan ) => {
            paste! {
                #[test]
                fn [<$name _iter >]() {
                    assert!(<&$iterty>::zscore($iter.iter()).all(|v| v.is_nan()));
                }
            }
        };
        ( $name:ident: $iterty:ty as $iter:expr => nan ) => {
            test_zscore!($name: $iterty as $iter ; into_iter => nan);
            test_zscore!($name: $iterty as $iter ; iter => nan);
        };
        ( $name:ident: $iterty:ty as $iter:expr; into_iter => $expected:expr ) => {
            paste! {
                #[test]
                fn [<$name _into_iter >]() {
                    let zscores: Vec<_> = <$iterty>::zscore($iter.into_iter()).collect();
                    assert_eq!(zscores, $expected);
                }
            }
        };
        ( $name:ident: $iterty:ty as $iter:expr; iter => $expected:expr ) => {
            paste! {
                #[test]
                fn [<$name _iter >]() {
                    let zscores: Vec<_> = <&$iterty>::zscore($iter.iter()).collect();
                    assert_eq!(zscores, $expected);
                }
            }
        };
        ( $name:ident: $iterty:ty as $iter:expr => $expected:expr ) => {
            test_zscore!($name: $iterty as $iter ; into_iter => $expected);
            test_zscore!($name: $iterty as $iter ; iter => $expected);
        };
    }

    test_zscore!(f64: f64 as [1.0, 2.0, 3.0, 4.0] => vec![-1.3416407864998738, -0.4472135954999579, 0.4472135954999579, 1.3416407864998738] );
    test_zscore!(f64_with_nan: f64 as [1.0, 2.0, 3.0, 4.0, f64::NAN] => nan );
    test_zscore!(f64_with_inf: f64 as [1.0, 2.0, 3.0, 4.0, f64::INFINITY] => nan );
    test_zscore!(f32: f32 as [1.0, 2.0, 3.0, 4.0] => vec![-1.3416407, -0.4472136, 0.4472136, 1.3416407] );
    test_zscore!(f32_with_nan: f32 as [1.0, 2.0, 3.0, 4.0, f32::NAN] => nan );
    test_zscore!(f32_with_inf: f32 as [1.0, 2.0, 3.0, 4.0, f32::INFINITY] => nan );
}