计算信息熵的简单做法

信息熵的简单做法

p*log(p)其中log函数是以2为底的函数，在C语言中，计算概率是可以应用换底公式来计算上面的公式。
直接贴代码了：

#include 
#include 
#include 
#include 
#include 

int GetSumCnt(std::map<std::string, int> &smap)
{
    int cnt_sum = 0;
    std::map<std::string, int>::iterator iter;
    for(iter = smap.begin(); iter != smap.end(); ++ iter)
        cnt_sum += iter->second;
    return cnt_sum;
}

int main()
{
    float score = 0.0, p_tmp = 0.0;
    int cnt = 0;
    int cnt_sum = 0;
    std::string str;
    std::map<std::string, int> smap;
    std::map<std::string, int>::iterator iter;

    str = "baidu";
    cnt = 3;
    smap[str] += cnt;
    score = 0.0;
    cnt_sum = GetSumCnt(smap);
    for(iter = smap.begin(); iter != smap.end(); ++ iter)
    {
        p_tmp = ((float)iter->second) / ((float)cnt_sum);
        printf("The p_tmp is %f\n", p_tmp);
        score -= p_tmp * (log(p_tmp) / log(2));
    }
    printf("The score is %f\n", score);


    str = "beijing";
    cnt = 3;
    smap[str] += cnt;
    score = 0.0;
    cnt_sum = GetSumCnt(smap);
    for(iter = smap.begin(); iter != smap.end(); ++ iter)
    {
        p_tmp = ((float)iter->second) / ((float)cnt_sum);
        printf("The p_tmp is %f\n", p_tmp);
        score -= p_tmp * (log(p_tmp) / log(2));
    }
    printf("The score is %f\n", score);

    str = "beijing";
    cnt = 3;
    smap[str] += cnt;
    score = 0.0;
    cnt_sum = GetSumCnt(smap);
    for(iter = smap.begin(); iter != smap.end(); ++ iter)
    {
        p_tmp = ((float)iter->second) / ((float)cnt_sum);
        printf("The p_tmp is %f\n", p_tmp);
        score -= p_tmp * (log(p_tmp) / log(2));
    }
    printf("The score is %f\n", score);
    return 0;
}

在此，主要想记录的是换底公式，在写代码的时候，可以让代码更加方便简洁一些。