Dictionary <float, Counts> AggregateByScore(ScoreTable table)
{
var matching = from score in table.Matching
select new { Score = score, Match = true };
var nonmatching = from score in table.NonMatching
select new { Score = score, Match = false };
var counted = from duplicate in matching.Concat(nonmatching)
group duplicate by duplicate.Score into grouped
select new
{
Score = grouped.Key,
Matching = grouped.Count(groupedDuplicate => groupedDuplicate.Match),
NonMatching = grouped.Count(groupedDuplicate => !groupedDuplicate.Match)
};
return(counted.ToDictionary(unique => unique.Score,
unique => new Counts {
Matching = unique.Matching, NonMatching = unique.NonMatching
}));
}
public void Compute(ScoreTable table)
{
Dictionary <float, Counts> countsByThreshold = AggregateByScore(table);
Counts totals = SumTotals(countsByThreshold.Values);
List <float> thresholds = new List <float>(countsByThreshold.Keys);
thresholds.Sort();
Curve = new List <ROCPoint>();
Counts seenBefore = new Counts();
foreach (float threshold in thresholds)
{
Counts counts = countsByThreshold[threshold];
// false matches are non-matching pairs at or above threshold
int falseMatches = totals.NonMatching - seenBefore.NonMatching;
// false rejects are matching pairs below threshold
int falseRejects = seenBefore.Matching;
ROCPoint point;
point.Threshold = threshold;
point.FAR = falseMatches / (float)totals.NonMatching;
point.FRR = falseRejects / (float)totals.Matching;
Curve.Add(point);
seenBefore.NonMatching += counts.NonMatching;
seenBefore.Matching += counts.Matching;
}
ROCPoint final;
final.Threshold = Curve[Curve.Count - 1].Threshold;
final.FAR = 0;
final.FRR = 1;
Curve.Add(final);
}
protected float GetAveragesDistance(ScoreTable table)
{
return(table.Matching.Average() - table.NonMatching.Average());
}
protected float GetMedianDistance(ScoreTable table)
{
return(table.Matching.Median() - table.NonMatching.Median());
}
public override float Measure(ScoreTable table)
{
return((table.Matching.Min() - table.NonMatching.Max()) / GetMedianDistance(table));
}
public abstract float Measure(ScoreTable table);
