MATLAB Programming

7 Working with Scientific Data Formats
strings. If that is not the mapping you intend, use HDF5 objects to specify
the correct mapping. In addition, note that HDF5 makes a distinction
between the size of a data set and the size of a data type. In MATLAB, data
types are always scalar. In HDF5, data types can have a size; that is, types
canbeeitherscalar(likeMATLAB)orm-by-n. InHDF5,a5-by-5dataset
containing a single uint8 value in each element is distinct from a 1-by-1 data
set containing a 5-by-5 array of uint8 values. In the first case, the data set
contains 25 observations of a single value; in the second case, the data set
contains a single observation with 25 values. For more information about
the MATLAB HDF5 data type objects, see “Mapping HDF5 Data Types to
MATLAB Data Types” on page 7-18.
Mapping HDF5 Data Types to MATLAB Data Types
When the hdf5read function reads data from an HDF5 file into the MATLAB
workspace, it maps HDF5 data types to MATLAB data types, depending on
whether the data in the data set is in an atomic data type or a nonatomic
composite data type.
Mapping Atomic Data Types. Atomic data types describe commonly used
binary formats for numbers (integers and floating point) and characters
(ASCII). Because different computing architectures and programming
languages support different number and character representations, the HDF5
library provides the platform-independent data types, which it then maps to
an appropriate data type for each platform. For example, a computer may
support 8-, 16-, 32-, and 64-bit signed integers, stored in memory in little
endian byte order.
If the data in the data set is stored in one of the HDF5 atomic data types,
hdf5read uses the equivalent MATLAB data type to represent the data. Each
data set contains a Datatype field that names the data type. For example,
the data set /g2/dset2.2 inthesampleHDF5fileincludesatomicdataand
data type information.
dtype = dataset1.Datatype
dtype =
Name: []
Class: 'H5T_IEEE_F32BE'
Elements: []
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