/// <summary>
/// Score a candidate doc for all slop-valid position-combinations (matches)
/// encountered while traversing/hopping the PhrasePositions.
/// <para/> The score contribution of a match depends on the distance:
/// <para/> - highest score for distance=0 (exact match).
/// <para/> - score gets lower as distance gets higher.
/// <para/>Example: for query "a b"~2, a document "x a b a y" can be scored twice:
/// once for "a b" (distance=0), and once for "b a" (distance=2).
/// <para/>Possibly not all valid combinations are encountered, because for efficiency
/// we always propagate the least PhrasePosition. This allows to base on
/// <see cref="Util.PriorityQueue{T}"/> and move forward faster.
/// As result, for example, document "a b c b a"
/// would score differently for queries "a b c"~4 and "c b a"~4, although
/// they really are equivalent.
/// Similarly, for doc "a b c b a f g", query "c b"~2
/// would get same score as "g f"~2, although "c b"~2 could be matched twice.
/// We may want to fix this in the future (currently not, for performance reasons).
/// </summary>
private float PhraseFreq()
{
if (!InitPhrasePositions())
{
return(0.0f);
}
float freq = 0.0f;
numMatches = 0;
PhrasePositions pp = pq.Pop();
int matchLength = end - pp.position;
int next = pq.Top.position;
while (AdvancePP(pp))
{
if (hasRpts && !AdvanceRpts(pp))
{
break; // pps exhausted
}
if (pp.position > next) // done minimizing current match-length
{
if (matchLength <= slop)
{
freq += docScorer.ComputeSlopFactor(matchLength); // score match
numMatches++;
}
pq.Add(pp);
pp = pq.Pop();
next = pq.Top.position;
matchLength = end - pp.position;
}
else
{
int matchLength2 = end - pp.position;
if (matchLength2 < matchLength)
{
matchLength = matchLength2;
}
}
}
if (matchLength <= slop)
{
freq += docScorer.ComputeSlopFactor(matchLength); // score match
numMatches++;
}
return(freq);
}
protected internal void PqToList()
{
last = first = null;
while (pq.Top() != null)
{
PhrasePositions pp = pq.Pop();
if (last != null)
{
// add next to end of list
last.next = pp;
}
else
{
first = pp;
}
last = pp;
pp.next = null;
}
}