//calculate backoff weight
static void output(string context, List <Ngram> vec_ngram, StreamWriter sw)
{
int idx = -1;
double numerator = 1.0;
double denominator = 1.0;
for (int i = 0; i < vec_ngram.Count; i++)
{
Ngram ngram = vec_ngram[i];
if (ngram.word == "")
{
idx = i;
}
else
{
numerator -= ngram.prob;
denominator -= ngram.lower;
}
}
// if no prefix context, cut off current n-gram
if (idx == -1)
{
return;
}
/**
* According to SRILM
* Avoid some predictable anomalies due to rounding errors
*/
bool valid = true;
if (numerator < 0.0 && numerator > -LM_EPSILON)
{
numerator = 0.0;
}
if (denominator < 0.0 && denominator > -LM_EPSILON)
{
denominator = 0.0;
}
if (denominator == 0.0 && numerator > LM_EPSILON)
{
numerator = 0.0;
}
else if (numerator < 0.0)
{
valid = false;
}
else if (denominator <= 0.0)
{
if (numerator > LM_EPSILON)
{
valid = false;
}
else
{
numerator = 0.0;
denominator = 0.0; // give bow = 0
}
}
double bow = 0;
if (valid)
{
bow = (numerator == 0.0 && denominator == 0.0) ?
0.0 : (prob2log(numerator) - prob2log(denominator));
}
else
{
bow = LM_LOG_ZERO;
}
sw.WriteLine("{0}\t{1} {2}", context, prob2log(vec_ngram[idx].prob), bow);
}
static void Main(string[] args)
{
if (args.Length != 2)
{
Console.WriteLine("common_bow.exe [input file] [output file]");
return;
}
StreamReader sr = new StreamReader(args[0]);
StreamWriter sw = new StreamWriter(args[1]);
SortedDictionary <string, List <Ngram> > kv = new SortedDictionary <string, List <Ngram> >();
string strLine = null;
while ((strLine = sr.ReadLine()) != null)
{
//For unigram, just duplicate input;
//For others, duplicate input, and split ngram into history\tword
//e.g. from h w\tvalue to h\tw\tvalue
string[] items = strLine.Split(new char[] { '\t' }, 2);
string key = items[0];
string value = items[1];
Ngram v = new Ngram();
v.word = "";
string[] strV = value.Split(' ');
v.prob = double.Parse(strV[0]);
v.lower = double.Parse(strV[1]);
if (kv.ContainsKey(key) == false)
{
kv.Add(key, new List <Ngram>());
}
kv[key].Add(v);
string[] keys = key.Split(' ');
if (keys.Length > 1)
{
string strKeys = String.Join(" ", keys, 0, keys.Length - 1).Trim();
v = new Ngram();
v.word = keys[keys.Length - 1];
v.prob = double.Parse(strV[0]);
v.lower = double.Parse(strV[1]);
if (kv.ContainsKey(strKeys) == false)
{
kv.Add(strKeys, new List <Ngram>());
}
kv[strKeys].Add(v);
}
}
sr.Close();
foreach (KeyValuePair <string, List <Ngram> > pair in kv)
{
output(pair.Key, pair.Value, sw);
}
sw.Close();
}
