h5_read: Reads and write object in HDF5 files

In grimbough/rhdf5: R Interface to HDF5

Reads and write object in HDF5 files

Description

Reads objects in HDF5 files. This function can be used to read either full arrays/vectors or subarrays (hyperslabs) from an existing dataset.

Usage

h5read(
  file,
  name,
  index = NULL,
  start = NULL,
  stride = NULL,
  block = NULL,
  count = NULL,
  compoundAsDataFrame = TRUE,
  callGeneric = TRUE,
  read.attributes = FALSE,
  drop = FALSE,
  ...,
  native = FALSE,
  s3 = FALSE,
  s3credentials = NULL
)

Arguments

file	The file name (character) of the file in which the dataset is be located. It is possible to provide an object of class H5IdComponent representing a H5 location identifier (file or group). See H5Fcreate, H5Fopen, H5Gcreate, H5Gopen to create an object of this kind.
name	The name of the dataset in the HDF5 file.
index	List of indices for subsetting. The length of the list has to agree with the dimensional extension of the HDF5 array. Each list element is an integer vector of indices. A list element equal to NULL chooses all indices in this dimension. Counting is R-style 1-based.
start	The start coordinate of a hyperslab (similar to subsetting in R). Counting is R-style 1-based. This argument is ignored, if index is not NULL.
stride	The stride of the hypercube. Read the introduction http://ftp.hdfgroup.org/HDF5/Tutor/phypecont.html before using this argument. R behaves like Fortran in this example. This argument is ignored, if index is not NULL.
block	The block size of the hyperslab. Read the introduction http://ftp.hdfgroup.org/HDF5/Tutor/phypecont.html before using this argument. R behaves like Fortran in this example. This argument is ignored, if index is not NULL.
count	The number of blocks to be read. This argument is ignored, if index is not NULL.
compoundAsDataFrame	If true, a compound datatype will be coerced to a data.frame. This is not possible, if the dataset is multi-dimensional. Otherwise the compound datatype will be returned as a list. Nested compound data types will be returned as a nested list.
callGeneric	If TRUE a generic function h5read.classname will be called if it exists depending on the dataset's class attribute within the HDF5 file. This function can be used to convert the standard output of h5read depending on the class attribute. Note that h5read is not a S3 generic function. Dispatching is done based on the HDF5 attribute after the standard h5read function.
read.attributes	(logical) If TRUE, the HDF5 attributes are read and attached to the respective R object.
drop	(logical) If TRUE, the HDF5 object is read as a vector with NULL dim attributes.
...	Further arguments passed to H5Dread.
native	An object of class logical. If TRUE, array-like objects are treated as stored in HDF5 row-major rather than R column-major orientation. Using native = TRUE increases HDF5 file portability between programming languages. A file written with native = TRUE should also be read with native = TRUE
s3	Logical value indicating whether the file argument should be treated as a URL to an Amazon S3 bucket, rather than a local file path.
s3credentials	A list of length three, providing the credentials for accessing files in a private Amazon S3 bucket.

Details

Read an R object from an HDF5 file. If none of the arguments start, stride, block, count are specified, the dataset has the same dimension in the HDF5 file and in memory. If the dataset already exists in the HDF5 file, one can read subarrays, so called hyperslabs from the HDF5 file. The arguments start, stride, block, count define the subset of the dataset in the HDF5 file that is to be read/written. See these introductions to hyperslabs: https://support.hdfgroup.org/HDF5/Tutor/selectsimple.html, https://support.hdfgroup.org/HDF5/Tutor/select.html and http://ftp.hdfgroup.org/HDF5/Tutor/phypecont.html. Please note that in R the first dimension is the fastest changing dimension.

When viewing the HDF5 datasets with any C-program (e.g. HDFView), the order of dimensions is inverted. In the R interface counting starts with 1, whereas in the C-programs (e.g. HDFView) counting starts with 0.

Special cases. There are a few instances where rhdf5 will make assumptions about the dataset you are reading and treat it slightly differently. 1) complex numbers. If your datasets is a compound datatype, has only two columns, and these are named 'r' and 'i' rhdf5 will assume the data is intended to be complex numbers and will read this into R's complex type. If that is not the case, you will need to extract the two values separately using the Re() and Im() accessors manually.

Value

h5read returns an array with the data read.

Author(s)

Bernd Fischer, Mike Smith

See Also

h5ls

Examples

h5File <- tempfile(pattern = "ex_hdf5file.h5")
h5createFile(h5File)

# write a matrix
B = array(seq(0.1,2.0,by=0.1),dim=c(5,2,2))
h5write(B, h5File, "B")

# read a matrix
E = h5read(h5File,"B")

# write and read submatrix
h5createDataset(h5File, "S", c(5,8), storage.mode = "integer", chunk=c(5,1), level=7)
h5write(matrix(1:5,nr=5,nc=1), file=h5File, name="S", index=list(NULL,1))
h5read(h5File, "S")
h5read(h5File, "S", index=list(NULL,2:3))

# Read a subset of an hdf5 file in a public S3 bucket

h5read('https://rhdf5-public.s3.eu-central-1.amazonaws.com/rhdf5ex_t_float_3d.h5', 
      s3 = TRUE, name = "a1", index = list(NULL, 3, NULL))

grimbough/rhdf5 documentation built on Sept. 14, 2024, 8:41 a.m.