fermentation 0.6.0

The good kind of decay; forward decay.
Documentation 
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
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187

use std::marker::PhantomData;
use std::time::Instant;
use crate::{ForwardDecay, Item};
use crate::aggregate::Aggregator;
use crate::g::{Exponential, Function};

/// Decayed aggregate sum, count and average over a stream of items.
///
/// ## Examples
/// ### Basic Aggregation
/// ```rust
/// use std::time::{Duration, Instant};
/// use fermentation::{ForwardDecay, g};
/// use fermentation::aggregate::{BasicAggregator, Aggregator};
///
/// let decay = ForwardDecay::new(Instant::now(), g::Polynomial::new(2));
/// let landmark = decay.landmark();
/// let now = landmark + Duration::from_secs(10);
/// let stream = vec![
///     (landmark + Duration::from_secs(5), 4.0),
///     (landmark + Duration::from_secs(7), 8.0),
///     (landmark + Duration::from_secs(3), 3.0),
///     (landmark + Duration::from_secs(8), 6.0),
///     (landmark + Duration::from_secs(4), 4.0),
/// ];
///
/// let mut aggregator = BasicAggregator::new(decay);
///
/// for item in stream {
///     aggregator.update(item);
/// }
///
/// let epsilon = 0.01;
///
/// assert_eq!(aggregator.sum(now), 9.67);
/// assert_eq!(aggregator.count(now), 1.63);
/// assert!(aggregator.average() >= (5.93 - epsilon) && aggregator.average() <= (5.93 + epsilon));
/// ```
///
/// ### Update Landmark
/// ```rust
/// use std::time::{Duration, Instant};
/// use fermentation::{ForwardDecay, g};
/// use fermentation::aggregate::{BasicAggregator, Aggregator};
///
/// let decay = ForwardDecay::new(Instant::now(), g::Exponential::new(0.2));
/// let landmark = decay.landmark();
/// let new_landmark = landmark + Duration::from_secs(1);
/// let now = landmark + Duration::from_secs(10);
/// let stream = vec![
///     (landmark + Duration::from_secs(5), 4.0),
///     (landmark + Duration::from_secs(7), 8.0),
///     (landmark + Duration::from_secs(3), 3.0),
///     (landmark + Duration::from_secs(8), 6.0),
///     (landmark + Duration::from_secs(4), 4.0),
/// ];
///
/// let mut aggregator = BasicAggregator::new(decay);
/// let mut clone = aggregator.clone();
///
/// clone.reset(new_landmark);
///
/// for item in stream {
///     aggregator.update(item);
///     clone.update(item);
/// }
///
/// aggregator.update_landmark(new_landmark);
///
/// let epsilon = 0.0001;
///
/// assert!((aggregator.sum(now) - clone.sum(now)).abs() < epsilon);
/// assert!((aggregator.count(now) - clone.count(now)).abs() < epsilon);
/// assert!((aggregator.average() - clone.average()).abs() < epsilon);
/// ```
#[derive(Copy, Clone)]
pub struct BasicAggregator<G, I> {
    decay: ForwardDecay<G>,
    sum: f64,
    count: f64,
    _phantom_data: PhantomData<I>
}

impl<G, I> Aggregator for BasicAggregator<G, I> where G: Function, I: Item {
    type Item = I;

    fn update(&mut self, item: I) {
        let static_weight = self.decay.static_weight(&item);

        self.sum += static_weight * item.value();
        self.count += static_weight;
    }

    fn reset(&mut self, landmark: Instant) {
        self.decay.set_landmark(landmark);
        self.sum = 0.0;
        self.count = 0.0;
    }
}

impl<I> BasicAggregator<Exponential, I>
where
    I: Item,
{
    pub fn update_landmark(&mut self, landmark: Instant) {
        let age = self.decay.set_landmark(landmark);
        let factor = self.decay.g().invoke(age);

        self.sum /= factor;
        self.count /= factor;
    }
}

impl<G, I> BasicAggregator<G, I>
where
    G: Function,
    I: Item,
{
    pub fn new(decay: ForwardDecay<G>) -> Self {
        Self {
            decay,
            sum: 0.0,
            count: 0.0,
            _phantom_data: Default::default()
        }
    }

    pub fn sum(&self, timestamp: Instant) -> f64 {
        self.sum / self.decay.normalizing_factor(timestamp)
    }

    pub fn static_sum(&self) -> f64 {
        self.sum
    }

    pub fn count(&self, timestamp: Instant) -> f64 {
        self.count / self.decay.normalizing_factor(timestamp)
    }

    pub fn static_count(&self) -> f64 {
        self.count
    }

    pub fn average(&self) -> f64 {
        self.sum / self.count
    }

    pub fn decay(&mut self) -> &ForwardDecay<G> {
        &self.decay
    }
}

#[cfg(test)]
mod tests {
    use std::ops::Add;
    use std::time::{Duration, Instant};
    use crate::g;
    use super::*;

    #[test]
    fn example() {
        let landmark = Instant::now();
        let now = landmark + Duration::from_secs(10);
        let stream = vec![
            (landmark.add(Duration::from_secs(5)), 4.0),
            (landmark.add(Duration::from_secs(7)), 8.0),
            (landmark.add(Duration::from_secs(3)), 3.0),
            (landmark.add(Duration::from_secs(8)), 6.0),
            (landmark.add(Duration::from_secs(4)), 4.0),
        ];

        let fd = ForwardDecay::new(landmark, g::Polynomial::new(2));
        let mut aggregator = BasicAggregator::new(fd);

        for item in stream {
            aggregator.update(item);
        }

        let epsilon = 0.01;

        assert_eq!(aggregator.sum(now), 9.67);
        assert_eq!(aggregator.static_sum(), 967.0);
        assert_eq!(aggregator.count(now), 1.63);
        assert_eq!(aggregator.static_count(), 163.0);
        assert!(aggregator.average() >= (5.93 - epsilon) && aggregator.average() <= (5.93 + epsilon));
    }
}