Sorting
cern.colt.matrix.objectalgo

## Class Sorting

• All Implemented Interfaces:
Serializable, Cloneable

public class Sorting
extends PersistentObject
Matrix quicksorts and mergesorts. Use idioms like Sorting.quickSort.sort(...) and Sorting.mergeSort.sort(...).

This is another case demonstrating one primary goal of this library: Delivering easy to use, yet very efficient APIs. The sorts return convenient sort views. This enables the usage of algorithms which scale well with the problem size: For example, sorting a 1000000 x 10000 or a 1000000 x 100 x 100 matrix performs just as fast as sorting a 1000000 x 1 matrix. This is so, because internally the algorithms only move around integer indexes, they do not physically move around entire rows or slices. The original matrix is left unaffected.

The quicksort is a derivative of the JDK 1.2 V1.26 algorithms (which are, in turn, based on Bentley's and McIlroy's fine work). The mergesort is a derivative of the JAL algorithms, with optimisations taken from the JDK algorithms. Mergesort is stable (by definition), while quicksort is not. A stable sort is, for example, helpful, if matrices are sorted successively by multiple columns. It preserves the relative position of equal elements.

GenericSorting, Sorting, Arrays, Serialized Form
• ### Field Detail

• #### quickSort

public static final Sorting quickSort
A prefabricated quicksort.
• #### mergeSort

public static final Sorting mergeSort
A prefabricated mergesort.
• ### Method Detail

• #### sort

public ObjectMatrix1D sort(ObjectMatrix1D vector)
Sorts the vector into ascending order, according to the natural ordering. The returned view is backed by this matrix, so changes in the returned view are reflected in this matrix, and vice-versa. To sort ranges use sub-ranging views. To sort descending, use flip views ...

Example:

 7, 1, 3, 1 ==> 1, 1, 3, 7 The vector IS NOT SORTED. The new VIEW IS SORTED.
Parameters:
vector - the vector to be sorted.
Returns:
a new sorted vector (matrix) view. Note that the original matrix is left unaffected.
• #### sort

public ObjectMatrix1D sort(ObjectMatrix1D vector,
Comparator c)
Sorts the vector into ascending order, according to the order induced by the specified comparator. The returned view is backed by this matrix, so changes in the returned view are reflected in this matrix, and vice-versa. The algorithm compares two cells at a time, determinining whether one is smaller, equal or larger than the other. To sort ranges use sub-ranging views. To sort descending, use flip views ...

Example:

// sort by sinus of cells
ObjectComparator comp = new ObjectComparator() {
public int compare(Object a, Object b) {
Object as = Math.sin(a); Object bs = Math.sin(b);
return as < bs ? -1 : as == bs ? 0 : 1;
}
};
sorted = quickSort(vector,comp);

Parameters:
vector - the vector to be sorted.
c - the comparator to determine the order.
Returns:
a new matrix view sorted as specified. Note that the original vector (matrix) is left unaffected.
• #### sort

public ObjectMatrix2D sort(ObjectMatrix2D matrix,
int column)
Sorts the matrix rows into ascending order, according to the natural ordering of the matrix values in the given column. The returned view is backed by this matrix, so changes in the returned view are reflected in this matrix, and vice-versa. To sort ranges use sub-ranging views. To sort columns by rows, use dice views. To sort descending, use flip views ...

Example:

 4 x 2 matrix: 7, 6 5, 4 3, 2 1, 0 column = 0; view = quickSort(matrix,column); System.out.println(view); ==> 4 x 2 matrix: 1, 0 3, 2 5, 4 7, 6 The matrix IS NOT SORTED. The new VIEW IS SORTED.
Parameters:
matrix - the matrix to be sorted.
column - the index of the column inducing the order.
Returns:
a new matrix view having rows sorted by the given column. Note that the original matrix is left unaffected.
Throws:
IndexOutOfBoundsException - if column < 0 || column >= matrix.columns().
• #### sort

public ObjectMatrix2D sort(ObjectMatrix2D matrix,
ObjectMatrix1DComparator c)
Sorts the matrix rows according to the order induced by the specified comparator. The returned view is backed by this matrix, so changes in the returned view are reflected in this matrix, and vice-versa. The algorithm compares two rows (1-d matrices) at a time, determinining whether one is smaller, equal or larger than the other. To sort ranges use sub-ranging views. To sort columns by rows, use dice views. To sort descending, use flip views ...

Example:

// sort by sum of values in a row
ObjectMatrix1DComparator comp = new ObjectMatrix1DComparator() {
public int compare(ObjectMatrix1D a, ObjectMatrix1D b) {
Object as = a.zSum(); Object bs = b.zSum();
return as < bs ? -1 : as == bs ? 0 : 1;
}
};
sorted = quickSort(matrix,comp);

Parameters:
matrix - the matrix to be sorted.
c - the comparator to determine the order.
Returns:
a new matrix view having rows sorted as specified. Note that the original matrix is left unaffected.
• #### sort

public ObjectMatrix3D sort(ObjectMatrix3D matrix,
int row,
int column)
Sorts the matrix slices into ascending order, according to the natural ordering of the matrix values in the given [row,column] position. The returned view is backed by this matrix, so changes in the returned view are reflected in this matrix, and vice-versa. To sort ranges use sub-ranging views. To sort by other dimensions, use dice views. To sort descending, use flip views ...

The algorithm compares two 2-d slices at a time, determinining whether one is smaller, equal or larger than the other. Comparison is based on the cell [row,column] within a slice. Let A and B be two 2-d slices. Then we have the following rules

• A < B iff A.get(row,column) < B.get(row,column)
• A == B iff A.get(row,column) == B.get(row,column)
• A > B iff A.get(row,column) > B.get(row,column)
Parameters:
matrix - the matrix to be sorted.
row - the index of the row inducing the order.
column - the index of the column inducing the order.
Returns:
a new matrix view having slices sorted by the values of the slice view matrix.viewRow(row).viewColumn(column). Note that the original matrix is left unaffected.
Throws:
IndexOutOfBoundsException - if row < 0 || row >= matrix.rows() || column < 0 || column >= matrix.columns().
• #### sort

public ObjectMatrix3D sort(ObjectMatrix3D matrix,
ObjectMatrix2DComparator c)
Sorts the matrix slices according to the order induced by the specified comparator. The returned view is backed by this matrix, so changes in the returned view are reflected in this matrix, and vice-versa. The algorithm compares two slices (2-d matrices) at a time, determinining whether one is smaller, equal or larger than the other. To sort ranges use sub-ranging views. To sort by other dimensions, use dice views. To sort descending, use flip views ...

Example:

// sort by sum of values in a slice
ObjectMatrix2DComparator comp = new ObjectMatrix2DComparator() {
public int compare(ObjectMatrix2D a, ObjectMatrix2D b) {
Object as = a.zSum(); Object bs = b.zSum();
return as < bs ? -1 : as == bs ? 0 : 1;
}
};
sorted = quickSort(matrix,comp);

Parameters:
matrix - the matrix to be sorted.
c - the comparator to determine the order.
Returns:
a new matrix view having slices sorted as specified. Note that the original matrix is left unaffected.