presage 0.9.1
recencyPredictor.cpp
Go to the documentation of this file.
1
2/******************************************************
3 * Presage, an extensible predictive text entry system
4 * ---------------------------------------------------
5 *
6 * Copyright (C) 2008 Matteo Vescovi <matteo.vescovi@yahoo.co.uk>
7
8 This program is free software; you can redistribute it and/or modify
9 it under the terms of the GNU General Public License as published by
10 the Free Software Foundation; either version 2 of the License, or
11 (at your option) any later version.
12
13 This program is distributed in the hope that it will be useful,
14 but WITHOUT ANY WARRANTY; without even the implied warranty of
15 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
16 GNU General Public License for more details.
17
18 You should have received a copy of the GNU General Public License along
19 with this program; if not, write to the Free Software Foundation, Inc.,
20 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
21 *
22 **********(*)*/
23
24
25#include "recencyPredictor.h"
26
27#include <math.h> // for exp()
28
31 ct,
32 name,
33 "RecencyPredictor, a statistical recency promotion predictor",
34 "RecencyPredictor, based on a recency promotion principle, generates predictions by assigning exponentially decaying probability values to previously encountered tokens. Tokens are assigned a probability value that decays exponentially with their distance from the current token, thereby promoting context recency." ),
35 dispatcher (this)
36{
37 // RecencyPredictor config variables
38 LOGGER = PREDICTORS + name + ".LOGGER";
39 LAMBDA = PREDICTORS + name + ".LAMBDA";
40 N_0 = PREDICTORS + name + ".N_0";
41 CUTOFF_THRESHOLD = PREDICTORS + name + ".CUTOFF_THRESHOLD";
42
43 // init default values
44 lambda = 1;
45 n_0 = 1;
47
52}
53
55{
56 // complete
57}
58
59void RecencyPredictor::set_lambda (const std::string& value)
60{
62 logger << INFO << "LAMBDA: " << value << endl;
63}
64
65void RecencyPredictor::set_n_0 (const std::string& value)
66{
67 n_0 = Utility::toDouble (value);
68 logger << INFO << "N_0: " << value << endl;
69}
70
71
72void RecencyPredictor::set_cutoff_threshold (const std::string& value)
73{
75 logger << INFO << "CUTOFF_THRESHOLD: " << value << endl;
76}
77
78
79Prediction RecencyPredictor::predict (const size_t max, const char** filter) const
80{
81 Prediction result;
82
83 std::string prefix = contextTracker->getPrefix();
84 logger << INFO << "prefix: " << prefix << endl;
85 if (!prefix.empty()) {
86 // Only build recency prediction if prefix is not empty: when
87 // prefix is empty, all previosly seen tokens are candidates
88 // for prediction. This is not desirable, because it means
89 // that recency prediction reduces to repetion of max previous
90 // tokens (i.e. the prediction would contain the most recent
91 // tokens in reverse order).
92 //
93 Suggestion suggestion;
94 size_t index = 1;
95 std::string token = contextTracker->getToken(index);
96 double prob = 0;
97 while (!token.empty() // context history exhausted
98 && result.size() < max // need only max suggestions
99 && index <= cutoff_threshold // look back only as far as cutoff
100 ) {
101 logger << INFO << "token: " << token << endl;
102
103 if (token.find(prefix) == 0) { // if token starts with prefix
104
105 if (token_satisfies_filter (token, prefix, filter)) {
106 // compute probability according to exponential decay
107 // formula
108 //
109 prob = n_0 * exp(-(lambda * (index - 1)));
110 logger << INFO << "probability: " << prob << endl;
111 suggestion.setWord(token);
112 suggestion.setProbability(prob);
113 result.addSuggestion(suggestion);
114 }
115
116 }
117
118 index++;
119 token = contextTracker->getToken(index);
120 }
121 }
122
123 return result;
124}
125
126void RecencyPredictor::learn(const std::vector<std::string>& change)
127{}
128
130{
131 logger << DEBUG << "About to invoke dispatcher: " << var->get_name () << " - " << var->get_value() << endl;
132 dispatcher.dispatch (var);
133}
Tracks user interaction and context.
std::string getToken(const int) const
std::string getPrefix() const
virtual std::string get_name() const =0
virtual std::string get_value() const =0
size_t size() const
Definition: prediction.cpp:68
void addSuggestion(Suggestion)
Definition: prediction.cpp:90
ContextTracker * contextTracker
Definition: predictor.h:83
const std::string PREDICTORS
Definition: predictor.h:81
virtual void set_logger(const std::string &level)
Definition: predictor.cpp:88
Logger< char > logger
Definition: predictor.h:87
const std::string name
Definition: predictor.h:77
virtual bool token_satisfies_filter(const std::string &token, const std::string &prefix, const char **filter) const
Definition: predictor.cpp:95
virtual void learn(const std::vector< std::string > &change)
std::string CUTOFF_THRESHOLD
Dispatcher< RecencyPredictor > dispatcher
std::string LOGGER
virtual Prediction predict(const size_t size, const char **filter) const
Generate prediction.
void set_n_0(const std::string &value)
std::string LAMBDA
virtual void update(const Observable *variable)
void set_lambda(const std::string &value)
RecencyPredictor(Configuration *, ContextTracker *, const char *)
void set_cutoff_threshold(const std::string &value)
void setWord(std::string)
Definition: suggestion.cpp:74
void setProbability(double)
Definition: suggestion.cpp:79
static double toDouble(const std::string)
Definition: utility.cpp:258
static int toInt(const std::string)
Definition: utility.cpp:266
const Logger< _charT, _Traits > & endl(const Logger< _charT, _Traits > &lgr)
Definition: logger.h:278
std::string config
Definition: presageDemo.cpp:70