C++

Forum

 
Exponential Moving Average with std:: map

simran07 (4)
hey guys,
i want to use exponential moving average with std::map. Actually what i have to do is whenever the duplicate key arrives during run time the mapped value of that key should be replace or update by the average value.
for example:
in map there are two pairs:
("a",4) and("b",8)
and when again the key value pair ("a",6) comes
the value in the map should become ("a",5) which is the average of 4 and 6 and same thing for key "b". And for this i need to use exponential moving average and i am confused with that. Please help me.. Thanks in advance...
BlakeK (54)
I don't know your situation, but could you use a std::multimap? You could store each occurrence in the multimap, then do the exponential average when needed and convert to a std::map in one function.
simran07 (4)
i can't use multimap my mentor told me to use map only he don't want that we store duplcate values...
ne555 (10692)
Provided that M[key] exists
M[key] = (M[key] + new_value)/2;
cire (8284)
I played around a bit. 

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
 
#include <stdexcept>
#include <iostream>
#include <string>
#include <map>

typedef std::map<std::string, double> map_type ;

const double smoothingFactor = .5 ;

double addDataPoint(map_type & m, map_type::value_type data)
{
    map_type::iterator it = m.find(data.first) ;

    if ( it == m.end() )
    {
        m[data.first] = data.second ;
        return data.second ;
    }

    return it->second = smoothingFactor * data.second + (1-smoothingFactor) * it->second ;
}

double getAverage(const map_type& m, const map_type::key_type & key )
{
    map_type::const_iterator it = m.find(key) ;
    if ( it == m.end() )
        throw std::logic_error( "getAverage called for non-existent key: \"" + key + '"') ;
    return it->second ;
}

std::ostream& operator<<(std::ostream& os, const map_type & map )
{
    map_type::const_iterator it ;
    for ( it = map.begin(); it != map.end(); ++it )
        os << it->first << ": " << it->second << '\n' ;
    return os ;
}

int main()
{
    map_type emaMap ;

    try
    {
        std::cout << "addDataPoint(\"a\", 4)\n" ;
        addDataPoint(emaMap, std::make_pair("a", 4)) ;
        std::cout << emaMap << '\n' ;

        std::cout << "addDataPoint(\"b\", 8)\n" ;
        addDataPoint(emaMap, std::make_pair("b", 8)) ;
        std::cout << emaMap << '\n' ;

        std::cout << "addDataPoint(\"a\", 6)\n" ;
        addDataPoint(emaMap, std::make_pair("a", 6)) ;
        std::cout << emaMap << '\n' ;

        std::cout << "addDataPoint(\"b\", 12)\n" ;
        addDataPoint(emaMap, std::make_pair("b", 12)) ;
        std::cout << emaMap << '\n' ;

        std::cout << "getAverage(\"a\")\n" ;
        std::cout << getAverage(emaMap, "a") << "\n\n" ;

        std::cout << "getAverage(\"b\")\n" ;
        std::cout << getAverage(emaMap, "b") << "\n\n" ;

        std::cout << "getAverage(\"c\")\n" ;
        std::cout << getAverage(emaMap, "c") << "\n\n" ;
    }
    catch (std::exception& ex)
    {
        std::cout << ex.what() << '\n' ;
    }
}


http://ideone.com/XXD34x

(Not sure what this has to do with UNIX/Linux programming!)
Topic archived. No new replies allowed.