Provided by: pdl_2.007-2build1_amd64 
NAME
PDL::IO::FastRaw -- A simple, fast and convenient io format for PerlDL.
VERSION
This documentation refers to PDL::IO::FastRaw version 0.0.2, I guess.
SYNOPSIS
use PDL;
use PDL::IO::FastRaw;
writefraw($pdl,"fname"); # write a raw file
$pdl2 = readfraw("fname"); # read a raw file
$pdl2 = PDL->readfraw("fname");
$pdl3 = mapfraw("fname2",{ReadOnly => 1}); # mmap a file, don't read yet
$pdl4 = maptextfraw("fname3",{...}); # map a text file into a 1-D pdl.
DESCRIPTION
This is a very simple and fast io format for PerlDL. The disk data consists of two files,
a header metadata file in ASCII and a binary file consisting simply of consecutive bytes,
shorts or whatever.
It is hoped that this will not only make for a simple PerlDL module for saving and
retrieving these files but also make it easy for other programs to use these files.
The format of the ASCII header is simply
<typeid>
<ndims>
<dim0> <dim1> ...
You should probably stick with the default header name. You may want to specify your own
header, however, such as when you have a large collection of data files with identical
dimensions and data types. Under these circumstances, simply specify the "Header" option
in the options hash.
The binary files are in general NOT 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.
It is also possible to mmap the file which can give a large speedup in certain situations
as well as save a lot of memory by using a disk file as virtual memory. When a file is
mapped, parts of it are read only as they are accessed in the memory (or as the kernel
decides: if you are reading the pages in order, it may well preread some for you).
Note that memory savings and copy-on-write are operating-system dependent - see Core.xs
and your operating system documentation for exact semantics of whatever. Basically, if you
write to a mmapped file without "ReadOnly", the change will be reflected in the file
immediately. "ReadOnly" doesn't really make it impossible to write to the piddle but maps
the memory privately so the file will not be changed when you change the piddle. Be aware
though that mmapping a 40Mb file without "ReadOnly" spends no virtual memory but with
"ReadOnly" it does reserve 40Mb.
Example: Converting ASCII to raw
You have a whole slew of data files in ASCII from an experiment that you ran in your lab.
You're still tweaking the analysis and plots, so you'd like if your data could load as
fast as possible. Eventually you'll read the data into your scripts using "readfraw", but
the first thing you might do is create a script that converts all the data files to raw
files:
#!/usr/bin/perl
# Assumes that the data files end with a .asc or .dat extension
# and saves the raw file output with a .bdat extension.
# call with
# >./convert_to_raw.pl file1.dat file2.dat ...
# or
# >./convert_to_raw.pl *.dat
use PDL;
use PDL::IO::FastRaw; # for saving raw files
use PDL::IO::Misc; # for reading ASCII files with rcols
while(shift) { # run through the entire supplied list of file names
($newName = $_) =~ s/\.(asc|dat)/.bdat/;
print "Saving contents of $_ to $newName\n";
$data = rcols($_);
writefraw($data, $newName);
}
Example: readfraw
Now that you've gotten your data into a raw file format, you can start working on your
analysis scripts. If you scripts used "rcols" in the past, the reading portion of the
script should go much, much faster now:
#!/usr/bin/perl
# My plotting script.
# Assume I've specified the files to plot on the command line like
# >./plot_script.pl file1.bdat file2.bdat ...
# or
# >./plot_script.pl *.bdat
use PDL;
use PDL::IO::FastRaw;
while(shift) { # run through the entire supplied list of file names
$data = readfraw($_);
my_plot_func($data);
}
Example: Custom headers
In the first example, I allow "writefraw" to use the standard header file name, which
would be "file.bdat.hdr". However, I often measure time series that have identical
length, so all of those header files are redundant. To fix that, I simply pass the Header
option to the "writefraw" command. A modified script would look like this:
#!/usr/bin/perl
# Assumes that the data files end with a .asc or .dat extension
# and saves the raw file output with a .bdat extension.
# call with
# >./convert_to_raw.pl [-hHeaderFile] <fileglob> [-hHeaderFile] <fileglob> ...
use PDL;
use PDL::IO::FastRaw; # for saving raw files
use PDL::IO::Misc; # for reading ASCII files with rcols
my $header_file = undef;
CL_OPTION: while($_ = shift @ARGV) { # run through the entire list of command-line options
if(/-h(.*)/) {
$header_file = $1;
next CL_OPTION;
}
($newName = $_) =~ s/\.(asc|dat)/.bdat/;
print "Saving contents of $_ to $newName\n";
$data = rcols($_);
writefraw($data, $newName, {Header => $header_file});
}
Modifying the read script is left as an exercise for the reader. :]
Example: Using mapfraw
Sometimes you'll want to use "mapfraw" rather than the read/write functions. In fact, the
original author of the module doesn't use the read/write functions anymore, prefering to
always use "mapfraw". How would you go about doing this?
Assuming you've already saved your data into the raw format, the only change you would
have to make to the script in example 2 would be to change the call to "readfraw" to
"mapfraw". That's it. You will probably see differences in performance, though I (David
Mertens) couldn't tell you about them because I haven't played around with "mapfraw" much
myself.
What if you eschew the use of "writefraw" and prefer to only use "mapfraw"? How would you
save your data to a raw format? In that case, you would have to create a "mapfraw" piddle
with the correct dimensions first using
$piddle_on_hd = mapfraw('fname', {Creat => 1, Dims => [dim1, dim2, ...]});
Note that you must specify the dimensions and you must tell "mapfraw" to create the new
piddle for you by setting the "Creat" option to a true value, not "Create" (note the
missing final 'e').
FUNCTIONS
readfraw
Read a raw format binary file
$pdl2 = readfraw("fname");
$pdl2 = PDL->readfraw("fname");
$pdl2 = readfraw("fname", {Header => 'headerfname'});
The "readfraw" command supports the following option:
Header Specify the header file name.
writefraw
Write a raw format binary file
writefraw($pdl,"fname");
writefraw($pdl,"fname", {Header => 'headerfname'});
The "writefraw" command supports the following option:
Header Specify the header file name.
mapfraw
Memory map a raw format binary file (see the module docs also)
$pdl3 = mapfraw("fname2",{ReadOnly => 1});
The "mapfraw" command supports the following options (not all combinations make sense):
Dims, Datatype
If creating a new file or if you want to specify your own header data for the
file, you can give an array reference and a scalar, respectively.
Creat Create the file. Also writes out a header for the file.
Trunc Set the file size. Automatically enabled with "Creat". NOTE: This also clears the
file to all zeroes.
ReadOnly
Disallow writing to the file.
Header Specify the header file name.
maptextfraw
Memory map a text file (see the module docs also).
Note that this function maps the raw format so if you are using an operating system which
does strange things to e.g. line delimiters upon reading a text file, you get the raw
(binary) representation.
The file doesn't really need to be text but it is just mapped as one large binary chunk.
This function is just a convenience wrapper which firsts "stat"s the file and sets the
dimensions and datatype.
$pdl4 = maptextfraw("fname", {options}
The options other than Dims, Datatype of "mapfraw" are supported.
BUGS
Should be documented better. "writefraw" and "readfraw" should also have options (the
author nowadays only uses "mapfraw" ;)
AUTHOR
Copyright (C) Tuomas J. Lukka 1997. All rights reserved. There is no warranty. You are
allowed to redistribute this software / documentation under certain conditions. For
details, see the file COPYING in the PDL distribution. If this file is separated from the
PDL distribution, the copyright notice should be included in the file.