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
use std::collections::HashMap;
use std::hash::Hash;
use std::iter;
mod weighted_set;
use weighted_set::WeightedSet;
#[derive(PartialEq, Eq, Hash, Clone, Debug)]
enum MarkovItem<I: Eq + Hash + Clone> {
Start,
Mid(I),
End,
}
type MarkovSymbolTable<I> = HashMap<Vec<MarkovItem<I>>, WeightedSet<MarkovItem<I>>>;
pub struct MarkovIterator<I: Eq + Hash + Clone> {
order: usize,
prev_symbols: Vec<MarkovItem<I>>,
symbols: MarkovSymbolTable<I>,
}
impl<I: Eq + Hash + Clone> Iterator for MarkovIterator<I> {
type Item = I;
fn next(&mut self) -> Option<I> {
self.prev_symbols
.push(self.symbols[&self.prev_symbols].choose().cloned()?);
if self.prev_symbols.len() > self.order {
self.prev_symbols.remove(0);
}
if let MarkovItem::Mid(symbol) = self.prev_symbols.iter().last().cloned()? {
Some(symbol)
} else {
None
}
}
}
#[derive(Clone, Debug)]
pub struct MarkovChain<I: Eq + Hash + Clone> {
order: usize,
symbols: MarkovSymbolTable<I>,
}
impl<I: Eq + Hash + Clone> MarkovChain<I> {
pub fn with_order<T>(order: usize) -> MarkovChain<I> {
MarkovChain {
order,
symbols: HashMap::new(),
}
}
fn update(&mut self, item: &[MarkovItem<I>], next_item: &MarkovItem<I>) {
if let Some(set) = self.symbols.get_mut(item) {
set.count(next_item);
} else {
let mut set = WeightedSet::default();
set.count(next_item);
self.symbols.insert(item.to_vec(), set);
}
}
pub fn feed(&mut self, input: impl Iterator<Item = I>) {
let items = iter::once(MarkovItem::Start)
.chain(input.map(move |i| MarkovItem::Mid(i.clone())))
.chain(iter::once(MarkovItem::End))
.collect::<Vec<_>>();
(1..self.order)
.map(|i| &items[..=i])
.chain(items.windows(self.order + 1))
.for_each(|window| {
let (present, past) = window.split_last().unwrap();
self.update(past, present);
});
}
}
impl<I: Eq + Hash + Clone> IntoIterator for MarkovChain<I> {
type Item = I;
type IntoIter = MarkovIterator<I>;
fn into_iter(self) -> Self::IntoIter {
let mut prev_symbols = Vec::with_capacity(2);
prev_symbols.push(MarkovItem::Start);
MarkovIterator {
order: self.order,
prev_symbols,
symbols: self.symbols,
}
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn chain() {
let mut chain = MarkovChain::with_order::<char>(1);
chain.feed("hello world".chars());
chain.feed("foo bar baz".chars());
println!("{}", chain.into_iter().collect::<String>());
}
}