Package smile.util

Class Array2D

java.lang.Object

smile.util.Array2D

public class Array2D
extends Object

2-dimensional array of doubles. Java doesn't have real multidimensional arrays. They are just array of arrays, which are not friendly to modern CPU due to frequent cache miss. The extra (multiple times) array index checking also significantly reduces the performance. This class solves these pain points by storing data in a single 1D array of doubles in row major order. Note that this class is simple by design, as a replacement of double[][] in case of row by row access. For advanced matrix computation, please use Matrix.

See Also:

• Matrix

Constructor Summary

Constructors

Constructor	Description
Array2D(double[][] A)	Constructor.
Array2D(int nrow, int ncol)	Constructor of all-zero matrix.
Array2D(int nrow, int ncol, double value)	Constructor.
Array2D(int nrow, int ncol, double[] value)	Constructor.

Method Summary

Modifier and Type	Method	Description
Array2D	add(double x)	A += x.
double	add(int i, int j, double x)	A[i, j] += x.
Array2D	add(Array2D B)	A += B.
double	apply(int i, int j)	Returns A[i, j].
Array2D	div(double x)	A /= x.
double	div(int i, int j, double x)	A[i, j] /= x.
Array2D	div(Array2D B)	A /= B.
double	get(int i, int j)	Returns A[i, j].
Array2D	mul(double x)	A *= x.
double	mul(int i, int j, double x)	A[i, j] *= x.
Array2D	mul(Array2D B)	A *= B.
int	ncol()	Returns the number of columns.
int	nrow()	Returns the number of rows.
Array2D	replaceNaN(double x)	Replaces NaN values with x.
void	set(int i, int j, double x)	Sets A[i, j].
Array2D	sub(double x)	A -= x.
double	sub(int i, int j, double x)	A[i, j] -= x.
Array2D	sub(Array2D B)	A -= B.
double	sum()	Returns the sum of all elements.
String	toString()
String	toString(boolean full)	Returns the string representation of matrix.
String	toString(int m, int n)	Returns the string representation of matrix.

Methods inherited from class java.lang.Object

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

Constructor Details

Array2D

public Array2D(double[][] A)

Constructor.

Parameters:

A - the array of matrix.

Array2D

public Array2D(int nrow,
 int ncol)

Constructor of all-zero matrix.

Parameters:

nrow - the number of rows.

ncol - the number of columns.

Array2D

public Array2D(int nrow,
 int ncol,
 double value)

Constructor. Fill the matrix with given value.

Parameters:

nrow - the number of rows.

ncol - the number of columns.

value - the initial value.

Array2D

public Array2D(int nrow,
 int ncol,
 double[] value)

Constructor.

Parameters:

nrow - the number of rows.

ncol - the number of columns.

value - the array of matrix values arranged in row major format.

Method Details

nrow

public int nrow()

Returns the number of rows.

Returns:

the number of rows.

ncol

public int ncol()

Returns the number of columns.

Returns:

the number of columns.

apply

public double apply(int i,
 int j)

Returns A[i, j]. Useful in Scala.

Parameters:

i - the row index.

j - the column index.

Returns:

A[i, j].

get

public double get(int i,
 int j)

Returns A[i, j].

Parameters:

i - the row index.

j - the column index.

Returns:

A[i, j].

set

public void set(int i,
 int j,
 double x)

Sets A[i, j].

Parameters:

i - the row index.

j - the column index.

x - the value.

add

public double add(int i,
 int j,
 double x)

A[i, j] += x.

Parameters:

i - the row index.

j - the column index.

x - the operand.

Returns:

the updated cell value.

sub

public double sub(int i,
 int j,
 double x)

A[i, j] -= x.

Parameters:

i - the row index.

j - the column index.

x - the operand.

Returns:

the updated cell value.

mul

public double mul(int i,
 int j,
 double x)

A[i, j] *= x.

Parameters:

i - the row index.

j - the column index.

x - the operand.

Returns:

the updated cell value.

div

public double div(int i,
 int j,
 double x)

A[i, j] /= x.

Parameters:

i - the row index.

j - the column index.

x - the operand.

Returns:

the updated cell value.

add

public Array2D add(Array2D B)

A += B.

Parameters:

B - the operand.

Returns:

this object.

sub

public Array2D sub(Array2D B)

A -= B.

Parameters:

B - the operand.

Returns:

this object.

mul

public Array2D mul(Array2D B)

A *= B.

Parameters:

B - the operand.

Returns:

this object.

div

public Array2D div(Array2D B)

A /= B.

Parameters:

B - the operand.

Returns:

this object.

add

public Array2D add(double x)

A += x.

Parameters:

x - the operand.

Returns:

this object.

sub

public Array2D sub(double x)

A -= x.

Parameters:

x - the operand.

Returns:

this object.

mul

public Array2D mul(double x)

A *= x.

Parameters:

x - the operand.

Returns:

this object.

div

public Array2D div(double x)

A /= x.

Parameters:

x - the operand.

Returns:

this object.

replaceNaN

public Array2D replaceNaN(double x)

Replaces NaN values with x.

Parameters:

x - the value.

Returns:

this object.

sum

public double sum()

Returns the sum of all elements.

Returns:

the sum of all elements.

toString

public String toString()

Overrides:

toString in class Object

toString

public String toString(boolean full)

Returns the string representation of matrix.

Parameters:

full - Print the full matrix if true. Otherwise, print only top left 7 x 7 submatrix.

Returns:

the string representation of matrix.

toString

public String toString(int m,
 int n)

Returns the string representation of matrix.

Parameters:

m - the number of rows to print.

n - the number of columns to print.

Returns:

the string representation of matrix.