private IEnumerable <Tuple <AffixInfo, Ngram <TItem> > > GetAffixes(Ngram <TItem> word, AffixType type)
{
Direction dir;
Dictionary <Ngram <TItem>, AffixInfo> affixes;
if (type == AffixType.Prefix)
{
dir = Direction.LeftToRight;
affixes = _prefixes;
}
else
{
dir = Direction.RightToLeft;
affixes = _suffixes;
}
var affix = new Ngram <TItem>();
yield return(Tuple.Create(affixes[affix], word));
foreach (TItem item in word.GetItems(dir).Take(Math.Min(MaxAffixLength, word.Length - 1)))
{
affix = affix.Concat(item, dir);
word = word.SkipFirst(dir);
AffixInfo ai;
if (affixes.TryGetValue(affix, out ai))
{
yield return(Tuple.Create(ai, word));
}
}
}
protected IEnumerable <AffixInfo> ComputeAffixes(ICollection <TSeq> sequences, AffixType type)
{
var dir = Direction.LeftToRight;
switch (type)
{
case AffixType.Prefix:
dir = Direction.LeftToRight;
break;
case AffixType.Suffix:
dir = Direction.RightToLeft;
break;
}
var affixFreqDist = new ConditionalFrequencyDistribution <int, Ngram <TItem> >();
var ngramFreqDist = new ConditionalFrequencyDistribution <int, Ngram <TItem> >();
var itemFreqDist = new FrequencyDistribution <TItem>();
var affixes = new Dictionary <Ngram <TItem>, AffixInfo>();
var nullAffix = new AffixInfo(sequences.Count, new Ngram <TItem>());
foreach (TSeq seq in sequences)
{
var wordNgram = new Ngram <TItem>(_syllablesSelector(seq).SelectMany(s => s));
nullAffix.Stems.Add(wordNgram);
foreach (TItem item in wordNgram)
{
itemFreqDist.Increment(item);
}
if (wordNgram.Length <= 1)
{
continue;
}
var items = new List <TItem>();
var syllableStart = new HashSet <int>();
foreach (IEnumerable <TItem> syllable in _syllablesSelector(seq).Items(dir))
{
items.AddRange(syllable.Items(dir));
syllableStart.Add(items.Count - 1);
}
var affix = new Ngram <TItem>();
var stem = new Ngram <TItem>(items, dir);
for (int i = 0; i < Math.Min(MaxAffixLength + 1, items.Count); i++)
{
affix = affix.Concat(items[i], dir);
affixFreqDist[affix.Length].Increment(affix);
if (i < items.Count - 1 && affix.Length <= MaxAffixLength)
{
AffixInfo ai = affixes.GetOrCreate(affix, () => new AffixInfo(sequences.Count, affix));
stem = stem.SkipFirst(dir);
ai.Stems.Add(stem);
if (syllableStart.Contains(i))
{
ai.SyllableBreakCount++;
}
}
}
for (int i = 0; i < items.Count; i++)
{
var ngram = new Ngram <TItem>();
for (int j = i; j < Math.Min(MaxAffixLength + i, items.Count); j++)
{
ngram = ngram.Concat(items[j], dir);
ngramFreqDist[ngram.Length].Increment(ngram);
}
}
}
var itemProbDist = new MaxLikelihoodProbabilityDistribution <TItem>(itemFreqDist);
var affixProbDist = new ConditionalProbabilityDistribution <int, Ngram <TItem> >(affixFreqDist, (c, fd) =>
{
if (c == 1)
{
return(new MaxLikelihoodProbabilityDistribution <Ngram <TItem> >(fd));
}
int binCount;
try
{
binCount = checked ((int)Math.Pow(itemFreqDist.ObservedSamples.Count, c));
}
catch (OverflowException)
{
binCount = int.MaxValue;
}
return(new WittenBellProbabilityDistribution <Ngram <TItem> >(fd, binCount));
});
var ngramProbDist = new ConditionalProbabilityDistribution <int, Ngram <TItem> >(ngramFreqDist, (c, fd) =>
{
if (c == 1)
{
return(new MaxLikelihoodProbabilityDistribution <Ngram <TItem> >(fd));
}
int binCount;
try
{
binCount = checked ((int)Math.Pow(itemFreqDist.ObservedSamples.Count, c));
}
catch (OverflowException)
{
binCount = int.MaxValue;
}
return(new WittenBellProbabilityDistribution <Ngram <TItem> >(fd, binCount));
});
foreach (AffixInfo affix in affixes.Values)
{
int freq = affixFreqDist[affix.Ngram.Length][affix.Ngram];
var maxCurveItem = itemFreqDist.ObservedSamples.Select(item => new { Item = item, Curve = (double)affixFreqDist[affix.Ngram.Length + 1][affix.Ngram.Concat(item, dir)] / freq })
.MaxBy(item => item.Curve);
double curveDrop = (1 - maxCurveItem.Curve) / (1 - itemProbDist[maxCurveItem.Item]);
double pw = affixProbDist[affix.Ngram.Length][affix.Ngram];
double npw = ngramProbDist[affix.Ngram.Length][affix.Ngram];
double randomAdj = npw == 0 ? 1.0 : pw / npw;
double normalizedFreq = affix.Ngram.Length * Math.Log(freq);
double syllableScore = AffixesOccurOnSyllableBoundaries ? (0.5 * ((double)affix.SyllableBreakCount / freq)) + 0.5 : 1.0;
affix.ZScore = curveDrop * randomAdj * normalizedFreq * syllableScore;
yield return(affix);
}
yield return(nullAffix);
}
