/// <summary>
/// Create a new RelationTable that is the inverse of this relation.
/// </summary>
/// <remarks>
/// Very useful for calculating, for example, pip dependents based on pip dependencies, or
/// per-file producers based on per-pip files produced.
/// </remarks>
public RelationTable <TToId, TFromId> Invert()
{
RelationTable <TToId, TFromId> result = new RelationTable <TToId, TFromId>(RelatedTable, BaseTableOpt);
// We will use result.Values to accumulate the counts as usual.
result.SingleValues.Fill(RelatedTable.Count, 0);
// And we will use result.m_offsets to store the offsets as usual.
result.Offsets.Fill(RelatedTable.Count, 0);
int sum = 0;
foreach (TFromId id in BaseTableOpt.Ids)
{
foreach (TToId relatedId in this[id])
{
result.SingleValues[relatedId.FromId() - 1]++;
sum++;
}
}
// Now we can calculate m_offsets.
result.CalculateOffsets();
// And we know the necessary size of m_relations.
result.MultiValues.Capacity = sum;
result.MultiValues.Fill(sum, default);
// Allocate an array of positions to track how many relations we have filled in.
SpannableList <int> positions = new SpannableList <int>(RelatedTable.Count + 1);
positions.Fill(RelatedTable.Count + 1, 0);
// And accumulate all the inverse relations.
foreach (TFromId id in BaseTableOpt.Ids)
{
foreach (TToId relatedId in this[id])
{
int relatedIdInt = relatedId.FromId() - 1;
int idInt = id.FromId() - 1;
int offset = result.Offsets[relatedIdInt];
int position = positions[relatedIdInt];
int relationIndex = result.Offsets[relatedIdInt] + positions[relatedIdInt];
result.MultiValues[relationIndex] = id;
positions[relatedIdInt]++;
if (positions[relatedIdInt] > result.SingleValues[relatedIdInt])
{
// this is a logic bug, should never happen
throw new Exception(
$"RelationTable.Inverse: logic exception: positions[{relatedIdInt}] = {positions[relatedIdInt]}, result.SingleValues[{relatedIdInt}] = {result.SingleValues[relatedIdInt]}");
}
else if (positions[relatedIdInt] == result.SingleValues[relatedIdInt])
{
// all the relations for this ID are known. now, we have to sort them.
Span <TFromId> finalSpan =
result.MultiValues.AsSpan().Slice(result.Offsets[relatedIdInt], result.SingleValues[relatedIdInt]);
SpanUtilities.Sort(finalSpan, (id1, id2) => id1.FromId().CompareTo(id2.FromId()));
}
}
}
// TODO: error check that there are no zero entries in m_relations
return(result);
}
/// <summary> /// Hashing. /// </summary> public int GetHashCode([DisallowNull] CharSpan obj) => SpanUtilities.GetHashCode(obj.AsSpan(m_stringTable), CharToInt);
