public static IEnumerable <int> GetColWeights(IBitMatrix matrix)
{
for (int col = 0; col < matrix.Cols; col++)
{
yield return(matrix.GetColWeight(col));
}
}
private IBitMatrix CompactMatrix()
{
var deletedRows = new bool[matrix.Rows];
var deletedCols = new bool[matrix.Cols];
ancestors = new Ancestor[matrix.Cols];
for (int i = 0; i < matrix.Cols; i++)
{
ancestors[i] = new Ancestor {
Column = i
}
}
;
if (diagnostics)
{
Console.WriteLine("initial density = {0:F3}/col", (double)matrix.GetRowWeights().Sum() / matrix.Rows);
}
int surplusCols = 0;
int pass = 1;
while (true)
{
int deleted = 0;
for (int n = matrix.Rows - 1; n >= 0; n--)
{
if (deletedRows[n])
{
continue;
}
var weight = matrix.GetRowWeight(n);
// Delete entirely empty rows.
if (weight == 0)
{
deletedRows[n] = true;
++surplusCols;
++deleted;
continue;
}
// Delete rows with a single non-zero entry.
if (weight == 1)
{
var col = matrix.GetNonZeroCols(n).First();
deletedRows[n] = true;
MergeColumns(col);
deletedCols[col] = true;
++deleted;
continue;
}
// Use surplus rows to bring weight down to merge limit.
int limit = Math.Min(pass, mergeLimit);
if (weight > limit && surplusCols > 0 && weight - surplusCols <= limit)
{
while (weight > limit)
{
var col = matrix.GetNonZeroCols(n)
.OrderByDescending(index => matrix.GetColWeight(index))
.First();
MergeColumns(col);
deletedCols[col] = true;
++deleted;
--surplusCols;
--weight;
}
}
// Merge low weight rows.
if (weight <= limit)
{
var cols = matrix.GetNonZeroCols(n)
.OrderByDescending(index => matrix.GetColWeight(index))
.ToArray();
Debug.Assert(cols.Length == weight);
var srcCol = cols[0];
MergeColumns(cols);
for (var ancestor = ancestors[srcCol]; ancestor != null; ancestor = ancestor.Next)
{
for (int j = 1; j < weight; j++)
{
ancestors[cols[j]] = new Ancestor {
Column = ancestor.Column, Next = ancestors[cols[j]]
}
}
;
}
deletedRows[n] = true;
ancestors[srcCol] = null;
deletedCols[srcCol] = true;
++deleted;
continue;
}
}
if (diagnostics)
{
Console.WriteLine("pass {0}: deleted {1} rows", pass, deleted);
}
if (deleted == 0)
{
break;
}
++pass;
}
// Compute mapping between original matrix and compact matrix.
ancestors = deletedCols
.Select((deleted, index) => deleted ? null : ancestors[index])
.Where(ancestor => ancestor != null)
.ToArray();
var rowMap = deletedRows
.Select((deleted, index) => deleted ? -1 : index)
.Where(index => index != -1)
.ToArray();
var colMap = deletedCols
.Select((deleted, index) => deleted ? -1 : index)
.Where(index => index != -1)
.ToArray();
// Permute columns to sort by increasing column weight.
var order = Enumerable.Range(0, colMap.Length)
.OrderBy(index => matrix.GetColWeight(colMap[index]))
.ToArray();
ancestors = Enumerable.Range(0, colMap.Length)
.Select(index => ancestors[order[index]])
.ToArray();
colMap = Enumerable.Range(0, colMap.Length)
.Select(index => colMap[order[index]])
.ToArray();
// Create compact matrix.
var revColMap = new int[matrix.Cols];
for (int i = 0; i < colMap.Length; i++)
{
revColMap[colMap[i]] = i;
}
var compactMatrix = (IBitMatrix)Activator.CreateInstance(typeof(TMatrix), rowMap.Length, colMap.Length);
for (int i = 0; i < rowMap.Length; i++)
{
int row = rowMap[i];
foreach (var col in matrix.GetNonZeroCols(row))
{
compactMatrix[i, revColMap[col]] = true;
}
}
if (diagnostics)
{
Console.WriteLine("completed compaction in {0} passes", pass);
Console.WriteLine("final density = {0:F3}/col", (double)matrix.GetRowWeights().Sum() / compactMatrix.Rows);
}
return(compactMatrix);
}
public static IEnumerable<int> GetColWeights(IBitMatrix matrix)
{
for (int col = 0; col < matrix.Cols; col++)
yield return matrix.GetColWeight(col);
}