HDF5-dump-management {HDF5Array} | R Documentation

## HDF5 dump management

### Description

A set of utilities to control the location of automatically created HDF5 datasets.

### Usage

    setHDF5DumpDir(dir)
    setHDF5DumpFile(filepath)
    setHDF5DumpName(name)
    setHDF5DumpCompressionLevel(level=6L)

    getHDF5DumpDir()
    getHDF5DumpFile(for.use=FALSE)
    getHDF5DumpName(for.use=FALSE)
    getHDF5DumpCompressionLevel()

    lsHDF5DumpFile()

    showHDF5DumpLog()

    ## For developers:
    getHDF5DumpChunkDim(dim, type, ratio=75)
    appendDatasetCreationToHDF5DumpLog(filepath, name, dim, type,
                                       chunkdim, level)

### Arguments

`dir` | The path (as a single string) to the current HDF5 dump directory, that is, to the (new or existing) directory where HDF5 dump files with automatic names will be created. This is ignored if the user specified an HDF5 dump file with `setHDF5DumpFile`. If `dir` is missing, then the HDF5 dump directory is set back to its default value i.e. to some directory under `tempdir()` (call `getHDF5DumpDir()` to get the exact path).
`filepath` | For `setHDF5DumpFile`: The path (as a single string) to the current HDF5 dump file, that is, to the (new or existing) HDF5 file where the next automatic HDF5 datasets will be written. If `filepath` is missing, then a new file with an automatic name will be created (in `getHDF5DumpDir()`) and used for each new dataset. For `appendDatasetCreationToHDF5DumpLog`: See the Note TO DEVELOPERS below.
`name` | For `setHDF5DumpName`: The name of the next automatic HDF5 dataset to be written to the current HDF5 dump file. For `appendDatasetCreationToHDF5DumpLog`: See the Note TO DEVELOPERS below.
`level` | For `setHDF5DumpCompressionLevel`: The compression level to use for writting automatic HDF5 datasets to disk. See the `level` argument in `?rhdf5::h5createDataset` (in the rhdf5 package) for more information about this. For `appendDatasetCreationToHDF5DumpLog`: See the Note TO DEVELOPERS below.
`for.use` | Whether the returned file or dataset name is for use by the caller or not. See below for the details.
`dim` | The dimensions of the HDF5 dataset to be written to disk, that is, an integer vector of length one or more giving the maximal indices in each dimension. See the `dims` argument in `?rhdf5::h5createDataset` (in the rhdf5 package) for more information about this.
`type` | The type (a.k.a. storage mode) of the data to be written to disk. Can be obtained with `type()` on an array-like object (which is equivalent to `storage.mode()` or `typeof()` on an ordinary array). This is typically what an application writing datasets to the HDF5 dump should pass to the `storage.mode` argument of its call to `rhdf5::h5createDataset`. See the Note TO DEVELOPERS below for more information.
`ratio` | The number of chunks per block. By default, a ratio of 75 is used.
`chunkdim` | The dimensions of the chunks.

### Details

Calling `getHDF5DumpFile()` and `getHDF5DumpName()` with no argument should be informative only i.e. it's a mean for the user to know where the next automatic HDF5 dataset will be written. Since a given file/name combination can be used only once, the user should be careful to not use that combination to explicitely create an HDF5 dataset because that would get in the way of the creation of the next automatic HDF5 dataset. See the Note TO DEVELOPERS below if you actually need to use this file/name combination.

`lsHDF5DumpFile()` is a just convenience wrapper for `rhdf5::h5ls(getHDF5DumpFile())`.

### Value

`getHDF5DumpDir` returns the absolute path to the directory where HDF5 dump files with automatic names will be created. Only meaningful if the user did NOT specify an HDF5 dump file with `setHDF5DumpFile`.

`getHDF5DumpFile` returns the absolute path to the HDF5 file where the next automatic HDF5 dataset will be written.

`getHDF5DumpName` returns the name of the next automatic HDF5 dataset.

`getHDF5DumpCompressionLevel` returns the compression level currently used for writting automatic HDF5 datasets to disk.

`showHDF5DumpLog` returns the dump log in an invisible data frame.

`getHDF5DumpChunkDim` returns the dimension of the chunks for the specified `ratio`. By default a ratio of 75 is used i.e. the automatic HDF5 dataset are written to disk using 75 chunks per block.

### Note

TO DEVELOPERS:

If your application needs to write its own dataset to the HDF5 dump then it should:

1. Get a file/name combination by calling `getHDF5DumpFile(for.use=TRUE)` and `getHDF5DumpName(for.use=TRUE)`.

2. [OPTIONAL] Call `getHDF5DumpChunkDim(dim, type)` (possibly with a non-default `ratio`) to get reasonable chunk dimensions to use for writting the data to disk. Or choose your own chunk dimensions.

3. Add an entry to the dump log by calling `appendDatasetCreationToHDF5DumpLog`. Typically, this should be done right after creating the dataset (e.g. with `rhdf5::h5createDataset`) and before starting to write the data to disk. The values passed to `appendDatasetCreationToHDF5DumpLog` via the `filepath`, `name`, `dim`, `type`, `chunkdim`, and `level` arguments should be those that were passed to `rhdf5::h5createDataset` via the `file`, `dataset`, `dims`, `storage.mode`, `chunk`, and `level` arguments, respectively. Note that `appendDatasetCreationToHDF5DumpLog` uses a lock mechanism so is safe to use in the context of parallel execution.

This is actually what the coercion method to HDF5Array does internally.

### See Also

- `writeHDF5Array` for writting an array-like object to an HDF5 file.

- HDF5Array objects.

- The `h5ls` function in the rhdf5 package, on which `lsHDF5DumpFile` is based.

- `type` in the DelayedArray package.

### Examples

    getHDF5DumpDir()
    getHDF5DumpFile()

    ## Use setHDF5DumpFile() to change the current HDF5 dump file.
    ## If the specified file exists, then it must be in HDF5 format or
    ## an error will be raised. If it doesn't exist, then it will be
    ## created.
    #setHDF5DumpFile("path/to/some/HDF5/file")

    lsHDF5DumpFile()

    a <- array(1:600, c(150, 4))
    A <- as(a, "HDF5Array")
    lsHDF5DumpFile()
    A

    b <- array(runif(6000), c(4, 2, 150))
    B <- as(b, "HDF5Array")
    lsHDF5DumpFile()
    B

    C <- (log(2 * A + 0.88) - 5)^3 * t(B[ , 1, ])
    as(C, "HDF5Array")  # realize C on disk
    lsHDF5DumpFile()

    ## Matrix multiplication is not delayed: the output matrix is realized
    ## block by block. The current "realization backend" controls where
    ## realization happens e.g. in memory if set to NULL or in an HDF5 file
    ## if set to "HDF5Array". See '?realize' in the DelayedArray package for
    ## more information about "realization backends".
    setRealizationBackend("HDF5Array")
    m <- matrix(runif(20), nrow=4)
    P <- C %*% m
    lsHDF5DumpFile()

    ## See all the HDF5 datasets created in the current session so far:
    showHDF5DumpLog()

    ## Wrap the call in suppressMessages() if you are only interested in the
    ## data frame version of the dump log:
    dump_log <- suppressMessages(showHDF5DumpLog())
    dump_log

[Package HDF5Array version 1.8.1 Index]