Module org.tensorflow.ndarray

Package org.tensorflow.ndarray

Interface NdArray<T>

Type Parameters:

T - the type of values to be mapped

All Superinterfaces:

Shaped

All Known Subinterfaces:

BooleanNdArray, ByteNdArray, DoubleNdArray, FloatNdArray, IntNdArray, LongNdArray, ShortNdArray, SparseNdArray<T,U>

All Known Implementing Classes:

AbstractDenseNdArray, org.tensorflow.ndarray.impl.AbstractNdArray, AbstractSparseNdArray, BooleanDenseNdArray, BooleanSparseNdArray, BooleanSparseSlice, ByteDenseNdArray, ByteSparseNdArray, ByteSparseSlice, DenseNdArray, DoubleDenseNdArray, DoubleSparseNdArray, DoubleSparseSlice, FloatDenseNdArray, FloatSparseNdArray, FloatSparseSlice, IntDenseNdArray, IntSparseNdArray, IntSparseSlice, LongDenseNdArray, LongSparseNdArray, LongSparseSlice, ObjectSparseSlice, ShortDenseNdArray, ShortSparseNdArray, ShortSparseSlice, SparseNdArray, SparseSlice

public interface NdArray<T>
extends Shaped

A data structure of N-dimensions.

The `NdArray` interface creates an abstraction between the physical storage of a data record, which can be linear or segmented, and its logical representation. In general, they achieve better performances than standard multi-dimensional arrays in Java by mapping directly linear data segments in memory.

Like DataBuffer, NdArray instances support 64-bits indexing so they can be used to map very large data records. They also support special coordinates that allow traversing their values in any direction or to select only a subset of them.

Example of usage:

    // Creates a 2x3x2 matrix (of rank 3)
    FloatNdArray matrix3d = NdArrays.ofFloats(shape(2, 3, 2));

    // Initialize sub-matrices data with vectors
    matrix.set(NdArrays.vectorOf(1.0f, 2.0f), 0, 0)
          .set(NdArrays.vectorOf(3.0f, 4.0f), 0, 1)
          .set(NdArrays.vectorOf(5.0f, 6.0f), 0, 2)
          .set(NdArrays.vectorOf(7.0f, 8.0f), 1, 0)
          .set(NdArrays.vectorOf(9.0f, 10.0f), 1, 1)
          .set(NdArrays.vectorOf(11.0f, 12.0f), 1, 2);

    // Access the second 3x2 matrix (of rank 2)
    FloatNdArray matrix = matrix3d.get(1);

    // Access directly the float value at (1, 0) from the second matrix
    assertEquals(9.0f, matrix.getFloat(1, 0));
 

Method Summary

Modifier and Type	Method	Description
NdArray<T>	copyTo(NdArray<T> dst)	Copy the content of this array to the destination array.
NdArraySequence<? extends NdArray<T>>	elements(int dimensionIdx)	Returns a sequence of all elements at a given dimension.
boolean	equals(Object obj)	Checks equality between n-dimensional arrays.
NdArray<T>	get(long... coordinates)	Returns the N-dimensional element of this array at the given coordinates.
T	getObject(long... coordinates)	Returns the value of the scalar found at the given coordinates.
NdArray<T>	read(DataBuffer<T> dst)	Read the content of this N-dimensional array into the destination buffer.
NdArraySequence<? extends NdArray<T>>	scalars()	Returns a sequence of all scalars in this array.
NdArray<T>	set(NdArray<T> src, long... coordinates)	Assigns the value of the N-dimensional element found at the given coordinates.
NdArray<T>	setObject(T value, long... coordinates)	Assigns the value of the scalar found at the given coordinates.
NdArray<T>	slice(Index... indices)	Creates a multi-dimensional view (or slice) of this array by mapping one or more dimensions to the given index selectors.
default Stream<T>	streamOfObjects()	Retrieve all scalar values of this array as a stream of objects.
NdArray<T>	write(DataBuffer<T> src)	Write the content of this N-dimensional array from the source buffer.

Methods inherited from interface org.tensorflow.ndarray.Shaped

rank, shape, size

Method Detail

elements

NdArraySequence<? extends NdArray<T>> elements(int dimensionIdx)

Returns a sequence of all elements at a given dimension.

Logically, the N-dimensional array can be flatten in a single vector, where the scalars of the (n - 1)th element precedes those of the (n)th element, for a total of Shaped.size() values.

For example, given a n x m matrix on the [x, y] axes, elements are iterated in the following order:

x₀y₀, x₀y₁, ..., x₀y_m-1, x₁y₀, x₁y₁, ..., x_n-1y_m-1

The returned sequence can then be iterated to visit each elements, either by calling Iterable.forEach(Consumer) or NdArraySequence.forEachIndexed(BiConsumer).

    // Iterate matrix for initializing each of its vectors
    matrixOfFloats.elements(0).forEach(v -> {
      v.set(vector(1.0f, 2.0f, 3.0f));
    });

    // Iterate a vector for reading each of its scalar
    vectorOfFloats.scalars().forEachIdx((coords, s) -> {
      System.out.println("Value " + s.getFloat() + " found at " + coords);
    });
 

Parameters:

dimensionIdx - index of the dimension

Returns:

an NdArray sequence

Throws:

IllegalArgumentException - if dimensionIdx is greater or equal to the total number of dimensions of this array

scalars

NdArraySequence<? extends NdArray<T>> scalars()

Returns a sequence of all scalars in this array.

This is equivalent to call elements(shape().numDimensions() - 1)

Returns:

an NdArray sequence

slice

NdArray<T> slice(Index... indices)

Creates a multi-dimensional view (or slice) of this array by mapping one or more dimensions to the given index selectors.

Slices allow to traverse an N-dimensional array in any of its axis and/or to filter only elements of interest. For example, for a given matrix on the [x, y] axes, it is possible to iterate elements at y=0 for all x.

Any changes applied to the returned slice affect the data of this array as well, as there is no copy involved.

Example of usage:

    FloatNdArray matrix3d = NdArrays.ofFloats(shape(3, 2, 4));  // with [x, y, z] axes

    // Iterates elements on the x axis by preserving only the 3rd value on the z axis,
    // (i.e. [x, y, 2])
    matrix3d.slice(all(), all(), at(2)).elements(0).forEach(m -> {
      assertEquals(shape(2), m); // y=2, z=0 (scalar)
    });

    // Creates a slice that contains only the last element of the y axis and elements with an
    // odd `z` coordinate.
    FloatNdArray slice = matrix3d.slice(all(), at(1), odd());
    assertEquals(shape(3, 2), slice.shape());  // x=3, y=0 (scalar), z=2 (odd coordinates)

    // Iterates backward the elements on the x axis
    matrix3d.slice(flip()).elements(0).forEach(m -> {
      assertEquals(shape(2, 4), m);  // y=2, z=4
    });
 

Parameters:

indices - index selectors per dimensions, starting from dimension 0 of this array.

Returns:

the element resulting of the index selection

Throws:

IndexOutOfBoundsException - if some coordinates are outside the limits of their respective dimension

get

NdArray<T> get(long... coordinates)

Returns the N-dimensional element of this array at the given coordinates.

Elements of any of the dimensions of this array can be retrieved. For example, if the number of coordinates is equal to the number of dimensions of this array, then a rank-0 (scalar) array is returned, which value can then be obtained by calling `array.getObject()`.

Any changes applied to the returned elements affect the data of this array as well, as there is no copy involved.

Note that invoking this method is an equivalent and more efficient way to slice this array on single scalar, i.e. array.get(x, y, z) is equal to array.slice(at(x), at(y), at(z))

Parameters:

coordinates - coordinates of the element to access, none will return this array

Returns:

the element at this index

Throws:

IndexOutOfBoundsException - if some coordinates are outside the limits of their respective dimension

set

NdArray<T> set(NdArray<T> src,
               long... coordinates)

Assigns the value of the N-dimensional element found at the given coordinates.

The number of coordinates provided can be anywhere between 0 and rank - 1. For example:

  FloatNdArray matrix = NdArrays.ofFloats(shape(2, 2));  // matrix rank = 2
  matrix.set(vector(10.0f, 20.0f), 0);  // success
  matrix.set(scalar(10.0f), 1, 0); // success
 

Parameters:

src - an array of the values to assign

coordinates - coordinates of the element to assign

Returns:

this array

Throws:

IndexOutOfBoundsException - if some coordinates are outside the limits of their respective dimension

getObject

T getObject(long... coordinates)

Returns the value of the scalar found at the given coordinates.

To access the scalar element, the number of coordinates provided must be equal to the number of dimensions of this array (i.e. its rank). For example:

  FloatNdArray matrix = NdArrays.ofFloats(shape(2, 2));  // matrix rank = 2
  matrix.getObject(0, 1);  // succeeds, returns 0.0f
  matrix.getObject(0);  // throws IllegalRankException

  FloatNdArray scalar = matrix.get(0, 1);  // scalar rank = 0
  scalar.getObject();  // succeeds, returns 0.0f
 

Note: if this array stores values of a primitive type, prefer the usage of the specialized method in the subclass for that type. For example, floatArray.getFloat(0); .

Parameters:

coordinates - coordinates of the scalar to resolve

Returns:

value of that scalar

Throws:

IndexOutOfBoundsException - if some coordinates are outside the limits of their respective dimension

IllegalRankException - if number of coordinates is not sufficient to access a scalar element

setObject

NdArray<T> setObject(T value,
                     long... coordinates)

Assigns the value of the scalar found at the given coordinates.

To access the scalar element, the number of coordinates provided must be equal to the number of dimensions of this array (i.e. its rank). For example:

  FloatNdArray matrix = NdArrays.ofFloats(shape(2, 2));  // matrix rank = 2
  matrix.setObject(10.0f, 0, 1);  // succeeds
  matrix.setObject(10.0f, 0);  // throws IllegalRankException

  FloatNdArray scalar = matrix.get(0, 1);  // scalar rank = 0
  scalar.setObject(10.0f);  // succeeds
 

Note: if this array stores values of a primitive type, prefer the usage of the specialized method in the subclass for that type. For example, floatArray.setFloat(10.0f, 0);

Parameters:

value - the value to assign

coordinates - coordinates of the scalar to assign

Returns:

this array

Throws:

IndexOutOfBoundsException - if some coordinates are outside the limits of their respective dimension

IllegalRankException - if number of coordinates is not sufficient to access a scalar element

streamOfObjects

default Stream<T> streamOfObjects()

Retrieve all scalar values of this array as a stream of objects.

For rank() > 1 arrays, all vectors of the last dimension are collated so that the scalar values are returned in sequential order.

Returns:

scalar values as a stream

copyTo

NdArray<T> copyTo(NdArray<T> dst)

Copy the content of this array to the destination array.

The Shaped.shape() of the destination array must be equal to the shape of this array, or an exception is thrown. After the copy, the content of both arrays can be altered independently, without affecting each other.

Parameters:

dst - array to receive a copy of the content of this array

Returns:

this array

Throws:

IllegalArgumentException - if the shape of dst is not equal to the shape of this array

read

NdArray<T> read(DataBuffer<T> dst)

Read the content of this N-dimensional array into the destination buffer.

The size of the buffer must be equal or greater to the Shaped.size() of this array, or an exception is thrown. After the copy, content of the buffer and of the array can be altered independently, without affecting each other.

Parameters:

dst - the destination buffer

Returns:

this array

Throws:

BufferOverflowException - if the buffer cannot hold the content of this array

See Also:

DataBuffer.size()

write

NdArray<T> write(DataBuffer<T> src)

Write the content of this N-dimensional array from the source buffer.

The size of the buffer must be equal or greater to the Shaped.size() of this array, or an exception is thrown. After the copy, content of the buffer and of the array can be altered independently, without affecting each other.

Parameters:

src - the source buffer

Returns:

this array

Throws:

BufferUnderflowException - if the buffer has not enough remaining data to write into this array

See Also:

DataBuffer.size()

equals

boolean equals(Object obj)

Checks equality between n-dimensional arrays.

An array is equal to another object if this object is another NdArray of the same shape, type and the elements are equal and in the same order. For example:

 IntNdArray array = NdArrays.ofInts(Shape.of(2, 2))
    .set(NdArrays.vectorOf(1, 2), 0)
    .set(NdArrays.vectorOf(3, 4), 1);

 assertEquals(array, StdArrays.ndCopyOf(new int[][] {{1, 2}, {3, 4}}));  // true
 assertEquals(array, StdArrays.ndCopyOf(new Integer[][] {{1, 2}, {3, 4}}));  // true, as Integers are equal to ints
 assertNotEquals(array, NdArrays.vectorOf(1, 2, 3, 4));  // false, different shapes
 assertNotEquals(array, StdArrays.ndCopyOf(new int[][] {{3, 4}, {1, 2}}));  // false, different order
 assertNotEquals(array, StdArrays.ndCopyOf(new long[][] {{1L, 2L}, {3L, 4L}}));  // false, different types
 

Note that the computation required to verify equality between two arrays can be expensive in some cases and therefore, it is recommended to not use this method in a critical path where performances matter.

Overrides:

equals in class Object

Parameters:

obj - object to compare this array with

Returns:

true if this array is equal to the provided object