PDL::IO (3)

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NAME

PDL::IO - An overview of the modules in the PDL::IO namespace.

SYNOPSIS

 # At your system shell, type:
 perldoc PDL::IO

DESCRIPTION

contains many modules for displaying, loading, and saving data.

*

Perlish or Text-Based

A few

IO

modules provide Perl-inspired capabilities. These are PDL::IO::Dumper and PDL::IO::Storable. PDL::IO::Misc provides simpler routines for dealing with delimited files, though its capabilities are limited to tabular or at most 3-d data sets.

*

Raw Format

PDL

has two modules that store their data in a raw binary format; they are PDL::IO::FastRaw and PDL::IO::FlexRaw. They are fast but the files they produce will not be readable across different architectures. These two modules are so similar that they could probably be combined.

*

Data Browsing

At the moment, only PDL::IO::Browser provides data browsing functionality.

*

Image Handling

PDL

has a handful of modules that will load images into piddles for you. They include PDL::IO::Dicom,

PDL::IO::FITS, PDL::IO::GD,

PDL::IO::Pic, and PDL::IO::Pnm. However,

PDL::IO::FITS

should also be considered something of a general data format.

*

Disk Caching

Both PDL::IO::FastRaw and PDL::IO::FlexRaw provide for direct piddle-to-disk mapping, but they use

PDL

's underlying mmap functionality to do it, and that doesn't work for Windows. However, users of all operating systems can still use PDL::DiskCache, which can use any desired

IO

read/write functionality (though you may have to write a small wrapper function).

*

General Data Storage Formats

PDL

has a number of modules that interface general data storage libraries. They include

PDL::IO::HDF

and

PDL::IO::NDF

(the latter is now a separate

CPAN

module). There is a

PDL::IO::IDL,

though at the moment it is not distributed with

PDL.

PDL::IO::FITS

is something of a general data format, since piddle data can be stored to a

FITS

file without loss. PDL::IO::FlexRaw and PDL::IO::FastRaw read and write data identical C's low-level "write" function and PDL::IO::FlexRaw can work with

FORTRAN 77 UNFORMATTED

files. FlexRaw and Storable provide general data storage capabilities. Finally,

PDL

can read Grib (weather-data) files using the

CPAN

module PDL::IO::Grib.

*

Making Movies

You can make an

MPEG

animation using PDL::IO::Pic's wmpeg function.

Here's a brief summary of all of the modules, in alphabetical order.

PDL::DiskCache

The DiskCache module allows you to tie a Perl array to a collection of files on your disk, which will be loaded into and out of memory as piddles. Although the module defaults to working with files, it allows you to specify your own reading and writing functions. This allows you to vastly streamline your code by hiding the unnecessary details of loading and saving files.

If you find yourself writing scripts to procss many data files, especially if that data processing is not necessarily in sequential order, you should consider using PDL::DiskCache. To read more, check the PDL::DiskCache documentation.

PDL::IO::Browser

The Browser module provides a text-based data browser for 2D data sets.

It uses the

library to do the scrolling, so if your operating system does not have the cureses library, you won't be able to install this on your machine. (Note that the package containing the header files for the library may be called "libcurses" or possibly "libncurses".)

PDL::IO::Browser is not installed by default because it gives trouble on Mac

and not enough is known to fix the problem. If you want to enable it, edit the perldl configuration file and rebuild To learn more about editing the configuration file, see the section in the . (Also, if you are familiar with on Mac, your help would be much appreciated!)

To see if the module is installed on your machine (and to get more information about PDL::IO::Browser), follow this link or type at the system prompt:

 perldoc PDL::IO::Browser

If you want to get more information about PDL::IO::Browser and it's not installed on your system, I'm afraid you'll have to pick out the pod from the source file, which can be found online at <pdl.git.sourceforge.net/git/gitweb.cgi?p=pdl/pdl;a=blob_plain;f=IO/Browser/browser.pd;hb=HEAD>.

PDL::IO::Dicom

is an image format, and this module allows you to read image files with the file format. To read more, check the PDL::IO::Dicom documentation.

PDL::IO::Dumper

Provides functionality similar to Data::Dumper for piddles. Data::Dumper stringifies a data structure, creating a string that can be "eval"ed to reproduce the original data structure. It's also usually suitable for printing, to visualize the structure.

To read more, check the PDL::IO::Dumper documentation. See also PDL::IO::Storable for a more comprehensive structured data solution.

PDL::IO::FastRaw

Very simple module for quickly writing, reading, and memory-mapping piddles to/from disk. It is fast to learn and fast to use, though you may be frustrated by its lack of options. To quote from the original

``The binary files are in general

interchangeable between different architectures since the binary file is simply dumped from the memory region of the piddle. This is what makes the approach efficient.''

This creates two files for every piddle saved - one that stores the raw data and another that stores the header file, which indicates the dimensions of the data stored in the raw file. Even if you save 1000 different piddles with the exact same dimensions, you will still need to write out a header file for each one. You cannot store multiple piddles in one file.

Note that at the time of writing, memory-mapping is not possible on Windows.

For more details, see PDL::IO::FastRaw. For a more flexible raw

module, see PDL::IO::FlexRaw.

PDL::IO::FITS

Allows basic reading and writing of files. You can read more about formatted files at <fits.gsfc.nasa.gov/fits_intro.html> and <en.wikipedia.org/wiki/FITS>. It is an image format commonly used in Astronomy.

This module may or may not be installed on your machine. To get more information, check online at <pdl.sourceforge.net/PDLdocs/IO/FITS.html>. To see if the module is installed on your machine, follow this link or type at the system prompt:

 perldoc PDL::IO::FITS

PDL::IO::FlexRaw

Somewhat smarter module (compared to FastRaw) for reading, writing, and memory mapping piddles to disk. In addition to everything that FastRaw can do, FlexRaw can also store multiple piddles in a single file, take user-specified headers (so you can use one header file for multiple files that have identical structure), and read compressed data. However, FlexRaw cannot memory-map compressed data, and just as with FastRaw, the format will not work across multiple architectures.

FlexRaw and FastRaw produce identical raw files and have essentially identical performance. Use whichever module seems to be more comfortable. I would generally recommend using FlexRaw over FastRaw, but the differences are minor for most uses.

Note that at the time of writing, memory-mapping is not possible on Windows.

For more details on FlexRaw, see PDL::IO::FlexRaw.

PDL::IO::GD

is a library for reading, creating, and writing bitmapped images, written in C. You can read more about the C-library here: <www.libgd.org>.

In addition to reading and writing .png and .jpeg files,

allows you to modify the bitmap by drawing rectangles, adding text, and probably much more. The documentation can be found here. As such, it should probably be not only considered an module, but a Graphics module as well.

This module provides

bindings for the library, which ought not be confused with the Perl bindings. The perl bindings were developed independently and can be found at , if you have Perl's bindings installed.

PDL::IO::Grib

A module last updated in 2000 that allows you to read Grib files. is a data format commonly used in meteorology. In the off-chance that you have it installed, you should read PDL::IO::Grib's documentation.

PDL::IO::HDF, PDL::IO::HDF5

Provides an interface to and file formats, which are kinda like cross-platform binary files. stands for Heierarchicl Data Format. was originally developed at the To read more about see <www.hdfgroup.org>. Note that is not presently distributed with and neither nor will be installed unless you have the associated C libraries that these modules interface. Also note that the library on is rather old and somebody from contacted the mailing list in the Fall of 2009 to develop new and better bindings for Perl.

You should look into the

(4) documentation or documentation, depending upon which module you have installed.

PDL::IO::IDL

Once upon a time, had a module for reading data files. Unfortunately, it cannot be distributed because the original author, Craig DeForest, signed the license agreement and was unable to negotiate the administrative hurdles to get it published. However, it can be found in Sourceforge's attic, and any user who has not signed 's license agreement can fix it up and resubmit it.

PDL::IO::Misc

Provides mostly text-based routines. Data input and output is restricted mostly to tabular (i.e. two-dimensional) data sets, though limited support is provided for 3d data sets.

Alternative text-based modules support higher dimensions, such as PDL::IO::Dumper and PDL::IO::Storable. Check the PDL::IO::Misc documentation for more details.

PDL::IO::NDF

Starlink developed a file format for N-Dimensional data Files, which it cleverly dubbed If you work with these files, you're in luck! Check the documentation for more details.

PDL::IO::Pic

Provides reading/writing of images to/from piddles, as well as creating animations! The module uses the netpbm library, so you will need that on your machine in order for this to work. To read more, see the PDL::IO::Pic documentation. Also look into the next module, as well as

PDL::IO::Pnm

Provides methods for reading and writing pnm files (of which pbm is but one). Check the PDL::IO::Pnm documentation for more details. Also check out the previous module and

PDL::IO::Storable

Implements the relevant methods to be able to store and retrieve piddles via Storable. True, you can use many methods to save a single piddle. In contrast, this module is particularly useful if you need to save a complex Perl structure that contain piddles, such as an array of hashes, each of which contains piddles.

Check the PDL::IO::Storable documentation for more details. See also PDL::IO::Dumper for an alternative stringifier.

COPYRIGHT

Copyright 2010 David Mertens (dcmertens.perl@gmail.com). You can distribute and/or modify this document under the same terms as the current Perl license.

See: dev.perl.org/licenses