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, 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>
    copyFrom(DataBuffer<T> src)
    Copy the content of the source buffer into this N-dimensional array.
    NdArray<T>
    copyTo(DataBuffer<T> dst)
    Copy the content of this N-dimensional array into the destination buffer.
    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.
    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>
    withShape(Shape shape)
    Returns a new N-dimensional view of this array with the given shape.

    Methods inherited from interface Shaped

    rank, shape, size

  • Method Details

    • 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, ..., x0ym-1, x1y0, x1y1, ..., xn-1ym-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

    • withShape

      NdArray<T> withShape(Shape shape)
      Returns a new N-dimensional view of this array with the given shape.

      The provided shape must comply to the following characteristics:

      • new shape is known (i.e. has no unknown dimension)
      • new shape size is equal to the size of the current shape (i.e. same number of elements)
      For example, 
         NdArrays.ofInts(Shape.scalar()).withShape(Shape.of(1, 1));  // ok
   NdArrays.ofInts(Shape.of(2, 3).withShape(Shape.of(3, 2));   // ok
   NdArrays.ofInts(Shape.scalar()).withShape(Shape.of(1, 2));  // not ok, sizes are different (1 != 2)
   NdArrays.ofInts(Shape.of(2, 3)).withShape(Shape.unknown()); // not ok, new shape unknown

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

      Parameters:
      shape - the new shape to apply
      Returns:
      a new array viewing the data according to the new shape, or this array if shapes are the same
      Throws:
      IllegalArgumentException - if the provided shape is not compliant
      UnsupportedOperationException - if this array does not support this operation

    • 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

    • copyTo

      NdArray<T> copyTo(DataBuffer<T> dst)
      Copy 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.

      Note: in version 0.4.0 and earlier, this method was named read(DataBuffer<T>). It has been renamed to explicitly indicate the direction of the data flow to avoid confusion.

      Parameters:
      dst - the destination buffer
      Returns:
      this array
      Throws:
      BufferOverflowException - if the buffer cannot hold the content of this array
      See Also:

    • copyFrom

      NdArray<T> copyFrom(DataBuffer<T> src)
      Copy the content of the source buffer into this N-dimensional array.

      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.

      Note: in version 0.4.0 and earlier, this method was named write(DataBuffer<T>). It has been renamed to explicitly indicate the direction of the data flow to avoid confusion.

      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:

    • 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