Package jline.util.matrix

Class RowView

  • All Implemented Interfaces:
    
public class RowView

    A lightweight view into a row of a sparse matrix that doesn't copy data. This provides efficient access to matrix row elements without the overhead of creating a new Matrix object and copying all the data.

    This is particularly useful for large sparse matrices where you need to access row elements frequently, such as in iterative algorithms.

    Example usage:

    Matrix bigMatrix = ...; // 1000 x 1M sparse matrix
RowView row = bigMatrix.getRowView(5);

// Efficient access - only processes non-zero elements
for (int i = 0; i < row.getNonZeroCount(); i++) {
    int col = row.getNonZeroCol(i);
    double value = row.getNonZeroValue(i);
    // process (col, value) pair
}

// Or get any element (returns 0.0 for non-stored elements)
double val = row.get(100);
    Since:

    1.0

    Author:

    QORE Lab, Imperial College London

    • Nested Class Summary

      Nested Classes 
      Modifier and Type Class Description

    • Field Summary

      Fields 
      Modifier and Type Field Description
      public final int rowIndex
      public final int numCols
      public final int nonZeroCount

    • Constructor Summary

      Constructors 
      Constructor Description

    • Enum Constant Summary

      Enum Constants 
      Enum Constant Description

    • Method Summary

      Modifier and Type Method Description
      int getRowIndex() Returns the row index that this view represents.
      int getNumCols() Returns the total number of columns in the row (including zeros).
      int getNonZeroCount() Returns the number of non-zero elements in this row.
      double dotProduct(Matrix columnVector) Computes the dot product of this row with a column vector.
      double get(int col) Returns the value at the specified column in this row.
      int getNonZeroCol(int i) Returns the column index of the i-th non-zero element in this row.
      double getNonZeroValue(int i) Returns the value of the i-th non-zero element in this row.
      boolean hasNonZeros() Checks if this row has any non-zero elements.

      • Methods inherited from class java.lang.Object

        clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

    • Constructor Detail

    • Method Detail

      • getRowIndex

         int getRowIndex()

        Returns the row index that this view represents.

        Returns:

        the row index

      • getNumCols

         int getNumCols()

        Returns the total number of columns in the row (including zeros).

        Returns:

        the number of columns

      • getNonZeroCount

         int getNonZeroCount()

        Returns the number of non-zero elements in this row.

        Returns:

        the count of non-zero elements

      • dotProduct

         double dotProduct(Matrix columnVector)

        Computes the dot product of this row with a column vector. This is optimized to only iterate through the non-zero elements of the row.

        Parameters:
        columnVector - the column vector to multiply with (must have getNumRows() == this.
        Returns:

        the scalar result of the dot product

      • get

         double get(int col)

        Returns the value at the specified column in this row. This method searches through the non-zero elements, so it's O(nnz_in_row). For frequent access to multiple elements, consider using the non-zero iterators.

        Parameters:
        col - the column index
        Returns:

        the value at (row, col), or 0.0 if not stored

      • getNonZeroCol

         int getNonZeroCol(int i)

        Returns the column index of the i-th non-zero element in this row.

        Parameters:
        i - the index into the non-zero elements (0 to getNonZeroCount()-1)
        Returns:

        the column index

      • getNonZeroValue

         double getNonZeroValue(int i)

        Returns the value of the i-th non-zero element in this row.

        Parameters:
        i - the index into the non-zero elements (0 to getNonZeroCount()-1)
        Returns:

        the value

      • hasNonZeros

         boolean hasNonZeros()

        Checks if this row has any non-zero elements.

        Returns:

        true if the row contains at least one non-zero element