HDF5 is a file format and library for storing and accessing data, commonly used for scientific data. HDF5 files can be created and read by numerous programming languages. This package provides an interface to the HDF5 library for the Julia language.

Please see HISTORY.md and the release notes. Most changes have deprecation warnings and may not be listed in the HISTORY.md file.

julia>]
pkg> add HDF5

For custom build instructions please refer to the documentation.

using HDF5

To read and write a variable to a file, one approach is to use the filename:

A = collect(reshape(1:120, 15, 8))
h5write("/tmp/test2.h5", "mygroup2/A", A)
data = h5read("/tmp/test2.h5", "mygroup2/A", (2:3:15, 3:5))

where the last line reads back just A[2:3:15, 3:5] from the dataset.

More fine-grained control can be obtained using functional syntax:

h5open("mydata.h5", "w") do file
    write(file, "A", A)  # alternatively, say "@write file A"
end

c = h5open("mydata.h5", "r") do file
    read(file, "A")
end

This allows you to add variables as they are generated to an open HDF5 file. You don't have to use the do syntax (file = h5open("mydata.h5", "w") works just fine), but an advantage is that it will automatically close the file (close(file)) for you, even in cases of error.

Julia's high-level wrapper, providing a dictionary-like interface, may also be of interest:

using HDF5

h5open("test.h5", "w") do file
    g = create_group(file, "mygroup") # create a group
    g["dset1"] = 3.2                  # create a scalar dataset inside the group
    attributes(g)["Description"] = "This group contains only a single dataset" # an attribute
end

Convenience functions for attributes attached to datasets are also provided:

A = Vector{Int}(1:10)
h5write("bar.h5", "foo", A)
h5writeattr("bar.h5", "foo", Dict("c"=>"value for metadata parameter c","d"=>"metadata d"))
h5readattr("bar.h5", "foo")