1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79

// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at http://mozilla.org/MPL/2.0/.

use num_traits::Num;

use signalo_traits::sink::Sink;

#[derive(Clone, Debug)]
struct State<T> {
    // number of values seen so far
    count: T,
    // mean of values seen so far
    mean: T,
}

/// A sink that computes the mean and variance of all received values of a signal.
#[derive(Clone, Default, Debug)]
pub struct Mean<T> {
    // The sink's state
    state: Option<State<T>>,
}

impl<T> Sink<T> for Mean<T>
where
    T: Copy + PartialOrd + Num,
{
    type Output = Option<T>;

    #[inline]
    fn sink(&mut self, input: T) {
        let (old_count, old_mean) = match self.state {
            Some(State { count, mean }) => (count, mean),
            None => (T::zero(), T::zero()),
        };

        let count = old_count + T::one();
        let mean = old_mean + ((input - old_mean) / count);

        self.state = Some(State { count, mean });
    }

    #[inline]
    fn finalize(self) -> Self::Output {
        self.state.map(|state| {
            let State { mean, .. } = state;
            mean
        })
    }
}

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

    #[test]
    fn empty() {
        let sink: Mean<f32> = Mean::default();
        let mean = sink.finalize();
        assert_nearly_eq!(mean, None);
    }

    #[test]
    fn non_empty() {
        // Sequence: https://en.wikipedia.org/wiki/Collatz_conjecture
        let input = vec![
            0.0, 1.0, 7.0, 2.0, 5.0, 8.0, 16.0, 13.0, 19.0, 6.0, 14.0, 9.0, 9.0, 17.0, 17.0, 4.0,
            12.0, 20.0, 20.0, 7.0, 7.0, 15.0, 15.0, 10.0, 23.0, 10.0, 111.0, 180.0, 108.0, 18.0,
            106.0, 5.0, 26.0, 13.0, 13.0, 21.0, 21.0, 21.0, 34.0, 8.0, 109.0, 8.0, 29.0, 16.0,
            16.0, 16.0, 104.0, 11.0, 24.0, 24.0,
        ];
        let mut sink = Mean::default();
        for input in input {
            sink.sink(input);
        }
        let mean = sink.finalize();
        assert_nearly_eq!(mean, Some(26.56));
    }
}