2. Generic dataset

Warning: This section is aimed at a Java developer.

A set of dataset classes are provided for the storage of n-dimensional arrays of Java primitive types.

A Scisoft dataset is a homogeneous collection of items where each item is accessed via a set of n (integer) indices - i.e. an n-D array. The location of an item as specified by n indices is called the position (of that item) in a dataset. An item can consist of number of elements - that number is fixed for each dataset class. The elements are of a single Java primitive type. The shape of a dataset is a set of positive integers which describe the upper bound of the indices given by a position. So 0 <= p_i < s_i for i = 0 to n-1.

The class hierarchy begins with the IDataset interface which allows interoperability with dataset classes external to the Scisoft plugin. This interface specifies the minimal set of methods that our plotting tools will use. An abstract base class is defined which contains dataset-neutral methods, common methods and static factory methods. A further abstract class extends the base class to allow datasets of compound elements.

2.1. IDataset

The following methods are declared:

public Class<?> elementClass();    // Java boxed primitive class

public int getElementsperitem();   // number of elements in each item

public int getItemsize();          // number of bytes in an item

public String getName();           // name of dataset

public void setName(String name);  // set name

public int getRank();              // rank of dataset

public int getSize();              // total number of elements in dataset

public int[] getShape();           // shape of dataset

public void setShape(final int... shape);  // set shape

public Object getObject(final int... pos); // item as an object in position

public double getDouble(final int... pos); // item as a double in position

public float getFloat(final int... pos);   // item as a float in position

public long getLong(final int... pos);       // item as a long in position

public int getInt(final int... pos);       // item as an int in position

public short getShort(final int... pos);   // item as a short in position

public byte getByte(final int... pos);     // item as a byte in position

public boolean getBoolean(final int... pos); // item as a boolean in position

public void set(Object obj, final int... pos); // set item in position

public Number min();               // minimum item in dataset

public Number max();               // maximum item in dataset

public int[] minPos();             // position of first minima

public int[] maxPos();             // position of first maxima

public IDataset getSlice(final int[] start, final int[] stop, final int[] step);
                               // slice of dataset

2.2. Implementation

A dataset is implemented as a 1-D backing array of elements. The items are stored so that elements are contiguous and the storage order is row-major. Items in a newly-created dataset are contiguous in the backing array.

An interface is specified for various dataset iterators. These iterators provide a means to iterate over the index of the backing data array and/or the positions in row-major order.

A dataset can be expanded by setting a value at a position outside its shape. Once expanded, the dataset can become discontiguous as extra space is reserved to allow for faster future expansion. A dataset can become contiguous again once it has expanded to fill its reserved space. Note that elements within the new shape but outside the old shape are set to minimum values or not-a-numbers.